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  • 1.
    Nilsson, Erik A.A
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pettersson, L.
    LKAB, Kiruna.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mn, Si and Ti in cast stainless steel at elevated temperature2019Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 46, nr 8, s. 731-741Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ACI HH II is an austenitic castable stainless steel for high-temperature applications such as grates in a Grate-Kiln indurator. Eight different alloy compositions have been used to evaluate the oxide formation and the microstructural evolution during an isothermal heat treatment at 800°C with a holding time of 200 h in an atmosphere containing 20% O2–N2. Residual ferrite is transformed into sigma phase during the heat treatment while secondary carbides are precipitated in the austenite. Silicon will form a thinner oxide but will reduce its adherence to the steel. Additions of Ti are beneficial for the properties of the oxide layer as the oxide is well adherent and thinner, while additions of Mn increase the growth rate of the oxide and enhance the risk of growth stresses in the oxide. It is proposed that by combing the beneficial effects of both Ti and Si it is possible to suppress the malign effects of Mn additions.

  • 2.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Woracek, Robin
    European Spallation Source ERIC, Lund, Sweden. Nuclear Physics Institute of the CAZ, Czech Republic.
    Maimaitiyili, T.
    Paul Scherrer Institute, Villigen.
    Scheffzük, Ch
    Karlsruhe Institute of Technology.
    Strobl, Markus
    Paul Scherrer Institute, Villigen, Switzerland. Nuclear Physics Institute of the CAZ, Czech Republic.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    University West, Trollhättan, Sweden.
    Bjerkén, Christina
    Malmö University, Sweden.
    Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction2018Ingår i: Additive Manufacturing, ISSN 2214-8604, Vol. 23, s. 225-234Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [112¯3].

  • 3.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Pederson, Robert
    Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Simon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Puyoo, Geraldine
    GKN-Aerospace Engine Systems.
    Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography2018Ingår i: Aeronautics and Aerospace Open Access Journal, ISSN 2576-4500, Vol. 2, nr 3, s. 139-145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electron beam melting (EBM) is emerging as a promising manufacturing process where metallic components are manufactured from three-dimensional (3D) computer aided design models by melting layers onto layers. There are several advantages with this manufacturing process such as near net shaping, reduced lead times and the possibility to decrease weight by topology optimization, aspects that are of interest for the aerospace industry. In this work two alloys, Ti-6Al-4V and Alloy 718, widely used within the aerospace industry were investigated with X-ray microtomography (XMT), to characterize defects such as lack of fusion (LOF) and inclusions. It was furthermore possible to view the macrostructure with XMT, which was compared to macrostructure images obtained by light optical microscopy (LOM). XMT proved to be a useful tool for defect characterization and both LOF and un-melted powder could be found in the two investigated samples. In the EBM built Ti-6Al-4V sample high density inclusions, believed to be composed of tungsten, were found. One of the high-density inclusions was found to be hollow, which indicate that the inclusion stems from the powder manufacturing process and not related with the EBM process. By performing defect analyses with the XMT software it was also possible to quantify the amount of LOF and un-melted powder in vol%. From the XMT-data meshes were produced so that finite element method (FEM) simulations could be performed. From these FEM simulations the significant impact of defects on the material properties was evident, as the defects led to high stress concentrations. It could moreover, with FEM, be shown that the as-built surface roughness of EBM material is of importance as high surface roughness led to increased stress concentrations.

  • 4.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Electron backscatter diffraction characterization of fatigue crack growth in laser metal wire deposited Ti-6Al-4V2018Ingår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, s. 245-256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By additive manufacturing (AM) there is a feasibility of producing near net shape components in basically one step from 3D CAD model to final product. The interest for AM is high and during the past decade a lot of research has been carried out in order to understand the influence from process parameters on the microstructure and furthermore on the mechanical properties. In the present study laser metal wire deposition of Ti-6Al-4V has been studied in detail with regard to its fatigue crack propagation characteristics. Two specimen orientations, parallel and perpendicular to the deposition direction, have been evaluated at room temperature and at 250 °C. No difference in the fatigue crack growth rate could be confirmed for the two specimen orientations. However, in the fractographic study it was observed that the tortuosity varied between certain regions on the fracture surface. The local crack path characteristic could be related to the alpha colony size and/or the crystallographic orientation. Moreover, large areas exhibiting similar crystallographic orientation were observed along the prior beta grain boundaries, which were attributed to the wide alpha colonies frequently observed along the prior beta grain boundaries.

  • 5.
    Rubin, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larker, R.
    Rubin-MaterialteknikLulea, Ausferritic ABVindeln.
    Navara, E.
    JihlavaCzechia.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Graphite Formation and Dissolution in Ductile Irons and Steels Having High Silicon Contents: Solid-State Transformations2018Ingår i: Metallography, Microstructure, and Analysis, ISSN 2192-9262, Vol. 7, nr 5, s. 587-595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Graphite formation in the solid state is both in ductile cast irons and in steels strongly promoted by high silicon contents above 3 wt.% Si. The matrix microstructure in austempered ductile iron can be further refined by secondary graphite if the austenitization, quench, and isothermal transformation into ausferrite are preceded by an austenitization at a slightly higher temperature followed by quench to martensite, resulting in higher carbon content than being soluble at the second austenitization temperature. Hypoeutectoid steels with high silicon contents can be rapidly graphitized, causing recrystallization of surrounding ferrite due to plastic deformation making room for less dense graphite. In rolled steels, the interface between manganese sulfide and steel matrix is the most common nucleation site. Voids are formed when graphite is partly or completely dissolved during austenitization in succeeding hardening heat treatments, but the mechanical properties can still be good if the graphite particles dissolved into voids are below 20 µm. Graphitized Si-solution strengthened ferritic steels may perform similar to free-cutting steels but with improved mechanical properties.

  • 6.
    Fargas, G.
    et al.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain , .
    Roa, J.J.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Sefer, Birhan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Pedersen, R.
    Division of Subtractive and Additive Manufacturing, University West, S-46186 Trollhaettan.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Matteo, A.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Influence of cyclic thermal treatments on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo alloy2018Ingår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 145, s. 218-224Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ti-6Al-2Sn-4Zr-2Mo is one of the most common titanium alloys for aerospace industry. This alloy experiences oxidation phenomenon at elevated temperatures. In the present study, cyclic thermal treatments were performed in air at 500, 593 and 700 °C, up to 500 cycles, in order to determine the oxidation kinetics and to analyze the oxide scale and alpha-case formation. Moreover, results were compared to those achieved under isothermal conditions to elucidate differences between both thermal conditions. In this sense, metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Field Emission Scanning Electron Microscopy and Focus Ions Beam, were used to analyze surface oxidation evolution. Results pointed out that cyclic treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed the formation of not only rutile, as isothermal treatments, but also anatase. Thickness of the oxide scale was higher for cyclic conditions, while alpha case did not exceed values reached by isothermal treatments and even became lower at 500 °C.

  • 7.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Division of Welding Technology, University West, Trollhättan 461 32, Sweden.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructural characterization and comparison of Ti-6Al-4V manufactured with different additive manufacturing processes2018Ingår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 143, nr SI, s. 68-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, the microstructures of Ti-6Al-4V manufactured by different additive manufacturing (AM) processes have been characterized and compared. The microstructural features that were characterized are the α lath thickness, grain boundary α (GB-α) thickness, prior β grain size and α colony size. In addition, the microhardnesses were also measured and compared. The microstructure of shaped metal deposited (SMD) Ti-6Al-4V material showed the smallest variations in α lath size, whereas the material manufactured with laser metal wire deposition-0 (LMwD-0) showed the largest variation. The prior β grain size was found to be smaller in material manufactured with powder bed fusion (PBF) as compared with corresponding material manufactured with the directed energy deposition (DED) processes. Parallel bands were only observed in materials manufactured with DED processes while being non-present in material manufactured with PBF processes.

  • 8.
    Ramanenka, Dmitrij
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gustafsson, Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Characterization of high-alumina refractory bricks and modelling of hot rotary kiln behaviour2017Ingår i: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, s. 852-864Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rotary kilns for iron-ore pellets production are highly dependent on a well-functioning refractory brick lining. To improve the long-term capability of the lining, in-situ observations of the bricks' performance are desired, however, the high process temperatures and the size of the kiln make it difficult to study the lining during operation. By using numerical simulations as a tool, some of the problems encountered by the brick lining can be studied. Knowing material properties of the refractory bricks as input in a numerical model is therefore necessary. However, material properties are poorly documented for this type of materials, especially, at elevated temperatures. In this work three commercial aluminasilicate bricks were tested in compression until failure for a temperature range of 25–1300 °C. The purpose was to evaluate compression strength and Young's modulus in compression of the fully burned bricks at a wide range of temperatures. The data was later used for modelling of a hot rotary kiln lined with bricks by using the finite element method, whereupon load state of the lining was evaluated at steady state after the expansion of the system. The objective of the numerical modelling was to investigate trustworthiness of the model and to give insight into the stress levels that can potentially arise. It was found that for all of the investigated brick types the compression strength increased with increased temperature, having a peak in the vicinity of 1000 °C. The maximum increase was between 50 and 150 % for the different brick types. After passing 1100 °C the compression strength rapidly and considerably decreased below its as-received compression strength. Young's modulus was measured to vary between 2 and 10 GPa in the range of up to 1000 °C. The numerical results indicate that severe boundary conditions (expansion of the lining is highly restricted) can potentially lead to compression stress of up to 34 MPa in the brick lining at steady state. However, at these boundary conditions the present tensile stress was only 0.5 MPa, while tensile stresses of close to 3 MPa could be observed in the lining with mild boundary conditions. The authors conclude that the created model is trustworthy and that it has high potential for being used as a tool in further investigations of the lining in hot state.

  • 9.
    Sefer, Birhan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya.
    Dobryden, Illia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Division of Surface and Corrosion Science, KTH Royal Institute of Technology.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Research and Technology Centre, GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions2017Ingår i: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, nr 4, s. 394-407Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the α-laths and the β-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the α-laths compared to the β-layers, in both alloys. In 1:3 solutions, higher α/β height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents.

  • 10.
    Nilsson, Erik A. A.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pettersson, Lars
    LKAB.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of Si, Mn and Ti on High Temperature Resistance of a Travelling Grate in a Grate-Kiln Indurator2017Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Artikel i tidskrift (Refereegranskat)
  • 11.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Pederson, Robert
    University West, Div. Welding Material .
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy2017Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The aim of this work has been to compare two different analysing methods;x-ray microtomography and light optical microscopy, when it comes to defects and microstructure of additively manufactured Ti-6Al-4V. The results showthat both techniqueshave theirpros and cons:microtomography is the preferred choicefor defect detectionby analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

  • 12.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Division of Welding Technology, University West, Trollhättan .
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure characterisation of Ti-6Al-4V from different additive manufacturing processes2017Ingår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 258, artikel-id 012007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The focus of this work has been microstructure characterisation of Ti-6Al-4V manufactured by five different additive manufacturing (AM) processes. The microstructure features being characterised are the prior β size, grain boundary α and α lath thickness. It was found that material manufactured with powder bed fusion processes has smaller prior β grains than the material from directed energy deposition processes. The AM processes with fast cooling rate render in thinner α laths and also thinner, and in some cases discontinuous, grain boundary α. Furthermore, it has been observed that material manufactured with the directed energy deposition processes has parallel bands, except for one condition when the parameters were changed, while the powder bed fusion processes do not have any parallel bands.

  • 13.
    Fargas, Gemma
    et al.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Universitat Politècnica de Catalunya, Barcelona.
    Roa, Joan Josep
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Universitat Politècnica de Catalunya, Barcelona.
    Sefer, Birhan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Universitat Politècnica de Catalunya, Barcelona.
    Pederson, Robert
    Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mateo, Antonio
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Oxidation behavior of Ti6Al4V alloy exposed to isothermal and cyclic thermal treatments2017Ingår i: METAL 2017: 26th International Conference on Metallurgy and Materials, Conference Proceedings, Ostrava: TANGER Ltd. , 2017, s. 1573-1579Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the most common titanium alloys for aerospace industry is Ti6Al4V (usually designed as Ti64) which is used for manufacturing aero-engine components, such as fan discs, compressor discs, blades and stators. The maximum service temperature for this alloy is limited partly because of degradation of mechanical properties at elevated temperatures (above 480 °C). During the first stage of oxidation the oxide scale is protective, whereas after prolonged oxidation time it loses its protective nature and favours higher diffusion of oxygen through the oxide. In the present study, cyclic thermal treatments were performed in air at 500 and 700 °C, up to 500 hours, and compared with similar studies carried out on isothermal oxidation conditions. The evolution of the surface oxidation was analyzed by metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Scanning Electron Microscopy and Focus Ions Beam. The results point out that the cyclic thermal treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed not only the presence of rutile, at 700 °C, but also anatase and TiOx at 500 °C for both isothermal and cyclic thermal treatments. At 700 °C, thermal stress caused by cyclic thermal treatments promoted the fracture of the oxide after the first 20 hours.

  • 14.
    Nilsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Thermal cycling of grate-link material for iron ore pelletising process2017Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, nr 4, s. 269-280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A test-rig for thermal cycling has been developed to investigate the mechanisms behind some of the damages done to a grate-link in a pelletising indurator for iron ore pellets. The results from the test-rig were compared with the degradation of grate-links that had been in service for 8 months in the indurator. The damages on the grate-links induced both in the test-rig and at service were defined as internal oxidation which facilitated propagation of intergranular stress corrosion cracking (IGSCC). Internal oxidation was initiated by spallation or removal of the oxide layers. The test-rig was able to successfully perform a lab-scale simulation of the degradation experienced in the indurator. Thermal cycling was applied to plate-formed specimens by constraining their thermal elongation to form bending and thereby stimulate the mechanisms of spallation and sensibilisation to IGSCC by internal oxidation.

  • 15.
    Norberg, Anders
    et al.
    Umeå University.
    Stöckel, Birgit
    Umeå University.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Time shifting and agile time boxes in course design2017Ingår i: International Review of Research in Open and Distance Learning, ISSN 1492-3831, E-ISSN 1492-3831, Vol. 18, nr 6, s. 88-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ongoing integration of Information and Communication Technologies (ICTs) into higher education courses is often called blended learning although it often relates to course design. It is usually understood in place categories, as a combination of traditional classroom-based sessions and Internet-enabled distance or online learning practices. One alternative understanding of ICT integration can be constructed of time categories, with an understanding of ICTs more as process- and project-related. Two such design frameworks are conceptually presented and then used together in a small case study in a pilot experiment in physics at the preparatory level for entering engineering programs at a university in Northern Sweden. These are a) time shift mechanisms between synchronous and asynchronous learning modes in the course process and b) agile frameworks mechanisms adapted from work process developments in the software industry. Both are here used to address common procrastination problems in flexible education. Data were collected in student interviews and analysed with qualitative content analysis. Results show student satisfaction with the work rhythm and that a feeling of presence, which enables easy interaction, can be facilitated by synchronicity.

  • 16.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A fractographic study exploring the relationship between the low cycle fatigue and metallurgical properties of laser metal wire deposited Ti-6Al-4V2016Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, s. 245-256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing (AM) has achieved large attention within the aerospace industry mainly because of the possibility to lower the material and the manufacturing cost. For titanium alloys several AM techniques are available today. In the present paper, the focus has been on laser metal wire-deposition of Ti-6Al-4V. Walls were built and low cycle fatigue specimens were cut out in two orientations with respect to the deposition direction. An extensive fractographic evaluation was carried out after testing and the results indicated anisotropic behaviour at low strain ranges. Defects such as pores and lack of fusion (LoF) were observed and related to the fatigue life and specimen orientation. The LoF defects are regarded to have the most detrimental influence on the fatigue life, whilst the effect of pores was not as straightforward. Noteworthy in present study is that one large LoF defect did not influence the fatigue life, which is explained by the prevalence of the LoF defect in relation to the loading direction.

  • 17.
    Sefer, Birhan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gaddam, Raghuveer
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Mateo, Antonio
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Chemical milling effect on the low cycle fatigue properties of cast Ti-6Al-2Sn-4Zr-2Mo alloy2016Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, nr 1, s. 193-202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The current research work presents the chemical milling effect on the low cycle fatigue properties of cast Ti-6Al-2Sn-4Zr-2Mo alloy. Chemical milling treatment is one of the final steps in manufacturing titanium alloy components that removes the brittle alpha-case layer formed during various thermal processes. The treatment includes immersion of the components in solutions containing hydrofluoric (HF) and nitric (HNO3) acids in relevant molar ratios. Although this treatment demonstrates advantages in handling components with complex net geometries, it may have detrimental effects on the surface, by introducing pitting and/or intergranular corrosion and thereby adversely affecting in particular the fatigue strength. The first series of specimens were tested in as-machined condition. Two more series were, prior to fatigue testing, subjected to 5 and 60 minutes chemical milling treatment. It was found that the fatigue lives were substantially decreased for the chemically treated specimens. The fractographic investigation of all mechanically tested samples revealed multiple fatigue crack initiation sites in the chemically milled samples. These cracks were located either at the prior beta grain boundary or the prior beta grain boundary triple joints. The prior beta grain boundaries were found to have deep ditch-like appearance which depth increased with increasing milling time. These ditch-like grain boundaries acts as stress raisers and thereby promote early fatigue crack initiation and thus lower fatigue life.

  • 18.
    Sefer, Birhan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Mateo, Antonio
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Evaluation of the bulk and alpha-case properties in Ti-6Al-4V at micro- and nano-metric length scale2016Ingår i: 13th World Conference on Titanium: August 16-20, 2015 * Manchester Grand Hyatt * San Diego, California / [ed] V. Venkatesh; A.L. Pilchak; J.E. Allison; S. Ankem; R. Boyer; J. Christodoulou; H.L. Fraser; M.A. Imam; J. Kosaka; H.J. Rack; A. Chaterjee; A. Woodfield, John Wiley and Sons , 2016, s. 1619-1624, artikel-id 271Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the present study the hardness of individual alpha (α)-Ti grains in Ti-6Al-4V was measured by nanoindentation using Berkovich tip indenter. Additionally, alpha-case layer was induced by performing isothermal heat treatment at 700°C in air for 500 hours. The average hardness of the α-Ti grains found in the bulk material and in the alpha-case layer were 6.7 ± 0.7 GPa and 9.4 ± 1.4 GPa, respectively. The high hardness of the α-Ti grains in the alpha-case layer is due to solid solution strengthening caused by interstitial oxygen diffusion. The thickness of the developed alpha-case layer was estimated metallographically and compared with that measured from a hardness profile performed along the layer. Moreover, electron back-scattered diffraction was used to determine the local crystallographic orientation, the texture of the alloy microstructure, as well as phase fraction changes, where the nanoindentation measurements were performed.

  • 19.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of microstructure on mechanical properties of laser metal wire-deposited Ti-6Al-4V2016Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, s. 428-437Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present paper laser metal wire deposition of Ti-6Al-4V has been studied and the mechanical properties evaluated. The yield strength, ultimate tensile strength and tensile elongation were all found to depend on the orientation of the specimens with respect to the deposition direction. Two orientations in the deposited material were evaluated in the study, perpendicular and parallel to the deposition direction. The specimens in the perpendicular orientation showed 25–33% higher elongation than the specimens parallel to the deposition direction. The parallel specimens on the other hand showed both higher (4%) ultimate tensile strength and higher (2–5%) yield strength. Furthermore, the anisotropic mechanical properties were correlated to the microstructural constituents of the specimens

  • 20.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona, Universitat Politècnica de Catalunya, Universidad de Extremadura.
    Material removal mechanisms by EDM of zirconia reinforced MWCNT nanocomposites2016Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, nr 5, s. 5792-5801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several composites of tetragonal zirconia polycrystals doped with 3 mol% yttria (3Y-TZP) and multiwalled carbon nanotubes (MWCNT) with concentrations from 0.5 to 4 wt% CNT were processed, spark plasma sintered, and characterised for a wide range of mechanical, electrical and thermal properties. In particular, a strong increase in electrical conductivity at room temperature was found with only 0.5 wt% CNT. However, the thermal conductivity was decreasing with increasing CNT content. Electrical discharge machining (EDM) using die sinking was carried out using the composites of 1 and 2 wt% CNT as workpieces. It was shown that both compositions could be successfully machined by EDM. The surface integrity and the subsurface were studied by SEM/FIB in order to determine the material removal mechanisms, which were found to be associated to spalling and melting/evaporation. Raman Spectroscopy was used to evaluate the damage of CNTs after EDM.

  • 21.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Turon-Vinas, Miquel
    CIEFMA—Department of Materials Science and Metallurgical Engineering, ETSEIB, Universitat Politècnica de Catalunya.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona, Universitat Politècnica de Catalunya, Universidad de Extremadura.
    Surface microstructural changes of Spark Plasma Sintered Zirconia after grinding and annealing2016Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, nr 14, s. 15610-15617Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spark plasma sintered zirconia (3Y-TZP) specimens have been produced of 140 nm 372 nm and 753 nm grain sizes by sintering at 1250 C, 1450 C and 1600 C, respectively. The sintered zirconia specimens were grinded using a diamond grinding disc with an average diamond particle size of about 60 µm, under a pressure of 0.9 MPa. The influence of grinding and annealing on the grain size has been analysed. It was shown that thermal etching after of ruff grinding of specimens at 1100 C for one hour induced an irregular surface layer of about a few hundred nanometres in thickness of recrystallized nano-grains, independently of the initial grain size. However, if the ground specimens were exposed to higher temperature, e.g. annealing at 1575 °C for one hour, the nano-grain layer was not observed and the final grain size was similar to that achieved by the same heat treatments on carefully polished specimens. Therefore, by appropriate grinding and thermal etching treatments, nanograined surface layer can be obtained which increases the resistance to low temperature degradation.

  • 22.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Turon-Vinas, Miquel
    CIEFMA—Department of Materials Science and Metallurgical Engineering, ETSEIB, Universitat Politècnica de Catalunya.
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona, Universitat Politècnica de Catalunya.
    The influence of unshielded small cracks in the fracture toughness of yttria and of ceria stabilised zirconia2016Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 36, nr 1, s. 147-153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fracture toughness, KIC of two 3Y–ZrO2 with different grain size (177 and 330 nm) and 12Ce–ZrO2 were determined from a sharp micro-machined notch by Ultra-Short Pulsed Laser Ablation (UPLA) where a micro-cracked zone and non-transformed is generated in front of the notch. The notch plus the damage behaved as an unshielded edge surface crack. The fracture stress, σf of both 330 nm-3Y–ZrO2 and 12Ce–ZrO2 with similar short crack sizes were found to be comparable in despite of their different published R-curves. The results of KIC were discussed in terms of the type of cracks induced and by using a simple R-curve model. It was concluded that for the development of high strength composites with 12Ce–ZrO2 as the matrix, the relevant KIC that controls the σf with surface unshielded short cracks is much closer to the intrinsic KIC than to the indentation KIC or to the plateau KIC of long cracks.

  • 23.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Coefficient of friction and wear resistance of zirconia-MWCNTs composites2015Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, nr 1 Part A, s. 459-468Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Composites of 3 mol.% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2 wt. % content have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4 and 97.4%. The addition of MWCNT content resulted in reduction of 3Y-TZP grain size from 174 to 148 nm. The effect of MWCNT on the friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Moreover, the COF and the wear rate were also investigated in reciprocating sliding against a zirconia ball under a load of 5 N. The results showed that the COF decreased upon the increase in MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing very slightly for less than 1 wt. % MWCNT, while it increases strongly for the addition of 2 wt. % MWCNT under the conditions studied. The results were discussed in terms of material properties, scanning electron microscopy observations of the wear track and nanoindentation tests.

  • 24.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Garcia-Marro, Fernando
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Milsom, Ben
    Department of Materials, Queen Mary College, University of London.
    Reece, Michael J.
    Department of Materials, Queen Mary College, University of London.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Nanoindentation and fracture toughness of nanostructured zirconia/multi-walled carbon nanotube composites2015Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, nr 2, s. 2453-2461Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multi-walled carbon nanotubes (MWCNTs)/3 mol% yttria-doped tetragonal zirconia (3Y-TZP) composites were produced using spark plasma sintering (SPS) with MWCNT content ranging within 0-2 wt%. In the present paper, it was shown that the addition of MWCNTs results in a refinement of the composites microstructure. Moreover, nanoindentation tests were performed in order to monitor the change in elastic modulus and hardness with MWCNT content and it was found that both properties decrease with the addition of MWCNT content. A novel method was used to measure the true fracture toughness of the composites by producing a shallow surface sharp notch machined by ultra-short pulsed laser ablation on the surface of beam specimens. The true fracture toughness obtained on this laser machined single edge V-notch beam (SEVNB) specimens tested in four point bending was compared to the indentation fracture toughness measured using a Vickers indenter. It was found that the indentation fracture toughness increases with increasing MWCNT content, while the true fracture toughness determined with SEVNB was practically independent of the composition. Finally, it was concluded that the increase in the resistance to indentation cracking of the composites with respect to 3Y-TZP matrix cannot be associated to higher true fracture toughness. The results were discussed in terms of transformation toughening, damage induced in front of the notch tip, microstructure of the composites, and fracture toughness of 3Y-TZP.

  • 25. Gaddam, Raghuveer
    et al.
    Sefer, Birhan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oxidation and alpha–case formation in Ti–6Al–2Sn–4Zr–2Mo alloy2015Ingår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 99, s. 166-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Isothermal heat treatments in ambient air were performed on wrought Ti–6Al–2Sn–4Zr–2Mo (Ti–6242) material at 500, 593 and 700 °C for times up to 500 hours. In presence of oxygen at elevated temperatures simultaneous reactions occurred in Ti–6242 alloy, which resulted in formation of an oxide scale and a layer with higher oxygen concentration (termed as alpha–case). Total weight gain analysis showed that there was a transition in the oxidation kinetics. At 500 °C, the oxidation kinetics obeyed cubic relationship up to 200 hours and thereafter changed to parabolic at prolonged exposure times. At 593 °C, it followed parabolic relationship. After heat treatment at 700 °C, the oxidation obeyed parabolic relationship up to 200 hours and thereafter changed to linear at prolonged exposure times. The observed transition is believed to be due to the differences observed in the oxide scale. The activation energy for parabolic oxidation was estimated to be 157 kJ/mol. In addition, alpha–case layer was evaluated using optical microscope, electron probe micro analyser and microhardness tester. The thickness of the alpha–case layer was found to be a function of temperature and time, increasing proportionally, and following parabolic relationship. The activation energy for formation of alpha–case layer was estimated to be 153 kJ/mol.

  • 26.
    Ekman, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Törlind, Peter
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Kuhn, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Nilsson, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Minami, Ichiro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zorzano Mier, María-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Grahn, Mattias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Parida, Vinit
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Behar, Etienne
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Wolf, Veronika
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Dordlofva, Christo
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Mendaza de Cal, Maria Teresa
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Jamali, Maryam
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Roos, Tobias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ottemark, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Nieto, Chris
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Soria Salinas, Álvaro Tomás
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Vázquez Martín, Sandra
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Nyberg, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Neikter, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lindwall, Angelica
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Fakhardji, Wissam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Projekt: Rymdforskarskolan2015Övrigt (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The Graduate School of Space Technology

  • 27.
    Escalera, Edwin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Garcia, Gustavo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Terán, R
    Chemistry Department, San Simon University.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Odén, Magnus
    The production of porous brick material from diatomaceous earth and Brazil nut shell ash2015Ingår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 98, s. 257-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diatomaceous earth was mixed with Brazil nut shell ash (BNS ash) in different amounts between 0 and 30 wt% and sintered at temperatures between 750 and 950 °C. The BNS ash contains 33 wt% K2O and 11 wt% CaO mainly in carbonate form. The addition of BNS ash into the diatomaceous earth caused significant changes of the microstructure after sintering. The BNS ash addition produces lightweight porous bricks with acceptable strength at lower sintering temperature. The best combination of strength and porosity was achieved for a mixture of 10 wt% of BNS ash in the diatomaceous earth sintered at 850 °C. The achieved high porosity was 49%, density 1.06 g/cm3, thermal conductivity 0.20 W/(m K) and the compressive strength was 8.5 MPa.

  • 28.
    Stöckel, Birgit
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Norberg, Anders
    Umeå universitet.
    Ett pilotförsök med time-based blended learning i basårskontext2014Ingår i: NU 2014: Umeå 8-10 oktober : abstracts, Umeå: Umeå universitet. Pedagogiska institutionen , 2014, s. 115-Konferensbidrag (Refereegranskat)
  • 29.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hörnqvist, Magnus
    GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fatigue crack growth behaviour of forged Ti-6Al-4V in gaseous hydrogen2014Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 78, s. 378-383Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fatigue crack growth (FCG) tests were performed to evaluate the fatigue behaviour of forged Ti-6Al-4V in air and high-pressure gaseous hydrogen (15 MPa) at room temperature. The results indicate that the effect of gaseous hydrogen is dependent on the stress intensity factor (ΔK). The FCG rate was unaffected by hydrogen below a critical stress intensity, ΔK* ≈ 20 MPa√m. Above ΔK*, the FCG rate fluctuated and subsequently accelerated at higher ΔK values. The observed behaviour is attributed to the change in the fracture processes. A hypothesis is proposed that describes the FCG behaviour in gaseous hydrogen.

  • 30.
    Escalera, Edwin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Odén, Magnus
    Linköpings universitet.
    High temperature phase evolution of Bolivian kaolinitic–illitic clays heated to 1250 °C2014Ingår i: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 101, s. 100-105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250 °C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650 °C. During further heating to 1050 °C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050–1150 °C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2 mass %) and Fe (5.6 mass%) has an onset temperature for sintering at about 900 °C and an onset temperature for liquid formation at 1080 °C. This is about 50 °C lower onset temperature for sintering and 94 °C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3 mass %) and Fe (1.6 mass %).

  • 31.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of alpha–case layer on the low cycle fatigue properties of Ti–6Al–2Sn–4Zr–2Mo alloy2014Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 599, s. 51-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Strain–controlled low cycle fatigue properties of Ti–6Al–2Sn–4Zr–2Mo with different thickness of alpha–case layers were investigated. Results show that at strain amplitudes 0.3 and 0.4%, the fatigue life of the alloy is reduced for the specimens with alpha–case layer compared to the ones without any alpha–case. It was noted that with a 2 μm thick alpha–case layer the low cycle fatigue life is reduced about 50% at the higher strain amplitude. The degrading effect of the alpha–case layer on fatigue life increased with increasing thickness. The alpha–case layer at the surface is enriched with oxygen making the surface harder and brittle, which results in easier crack initiation and thus decrease in fatigue life.

  • 32. Gaddam, Raghuveer
    et al.
    Hörnqvist, M.
    Department of Applied Physics, Chalmers University of Technology.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of High-pressure gaseous Hydrogen on the low-cycle fatigue and fatigue crack growth properties of a cast titanium alloy2014Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 612, s. 354-362Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present study, the effect of gaseous hydrogen on the fatigue properties of a commonly used aerospace titanium alloy (Ti–6Al–4 V) was studied. The low-cycle fatigue and fatigue crack growth properties were investigated at room temperature in ambient air and 15 MPa gaseous hydrogen. Results showed that the low-cycle fatigue life was significantly reduced in hydrogen, and the detrimental effect was larger at higher strain amplitudes. The fatigue crack growth rate in hydrogen remained unaffected below a critical stress intensity ΔK⁎≈17 MPa√m, while beyond this value, the fatigue crack growth rate fluctuated and increased with increasing ΔK. Fractography analysis clearly showed that gaseous hydrogen mainly affected the fatigue crack growth rate. On the fracture surfaces, striations were noted over the entire crack growth region in air, whereas in hydrogen striations were noted at stress intensities lower than ΔK⁎. Above ΔK⁎, secondary cracks and brittle flat surfaces with features similar to crack arrest marks were mostly observed in hydrogen. Microstructural analysis along the crack growth direction showed that the crack followed a transgranular path in air, i.e. through α colonies. In hydrogen, the crack also grew along the prior β grain boundaries and at α/β interface within the α colonies. Thereby, the detrimental effect of hydrogen in cast titanium alloy was attributed to a change in the fracture process during crack propagation

  • 33.
    Sefer, Birhan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gaddam, Raghuveer
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. GKN Aerospace Engine Systems Sweden.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Study of the Alpha-Case Layer in Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V by Electron Probe Micro Analysis2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Titanium and its alloys are susceptible to oxidation when exposed to elevated temperatures and oxygen containing environments for long exposure times, e.g. in jet engines [1–3]. In such conditions oxygen rapidly reacts with titanium, stabilizing α–titanium and forming solid solution due to the high solubility of oxygen in titanium (14.5 wt.%) [4]. The oxidation results in simultaneous formation of oxide scale on top of the metal and a brittle oxygen enriched layer beneath the scale, commonly referred as alpha–case. Alpha–case layer reduces important mechanical properties such as ductility, fracture toughness, and most severe reduces the fatigue life of jet engine components when subjected to dynamical loadings [5]. Therefore, the alpha-case layer in aerospace applications is usually removed by chemical milling [1–3] or prevented by using vacuum environments and high temperature coatings [1–3,6–9]. In the present study alpha–case in Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V alloys was developed by performing isothermal heat treatments at 700 °C in ambient air for 500 hours. The developed alpha–case layer was evaluated metallographically and by using instrumental techniques. It was found that the alpha–case development is a function of alloy composition and microstructure. The oxygen and the main alloying elements concentration profiles were measured using Electron Probe Micro Analyzer (EPMA) in both alloys. Based on the analysis of the concentration profiles an increase of the amount of alpha phase in the two alloys was found as a result of beta to alpha phase transformation.

  • 34.
    Nilsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pettersson, L.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Case study of grate-chain degradation in a grate-kiln process2013Ingår i: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, artikel-id 12012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Austenitic stainless steels are often used in high temperature applications due to their inherent resistance to corrosion. The grate-chain in some Grate-Kiln processes for sintering of iron pellets is made of these austenitic steels to withstand the severe environment. It has been shown however that the grate-chain is affected by several degrading mechanisms in the harsh environment of the sintering process. A grate-chain that had been used for 13 months in production was investigated in order to find the mechanisms of degradation. Results show that slag products are accumulated on the grate-chain during time and interact with the steel mainly due to the content of alkali metals. The resistance towards degradation seems to decrease with time which is suggested to be caused by the depletion of chromium.

  • 35.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hörnqvist, Magnus
    GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of hydrogen environment on fatigue crack growth in forged Ti-6Al-4V: fractographic analysis2013Ingår i: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, artikel-id 1210Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this study, the influence of hydrogen environment (15 MPa) on the fatigue crack growth in forged Ti-6A1-4V at room temperature is investigated. It is observed that at 21 < ΔK > 25 MPa√m, there exists a change of fatigue crack growth rate (FCGR) in hydrogen environment, and it is accelerated at ΔK > 25MPa√m. FCGR in hydrogen environment is dependent on the stress intensity levels (ΔK). Detailed fractographic analysis of the fracture surfaces were performed at different ΔK using high-resolution scanning electron microscope (HR-SEM). Fatigue striations were observed in air and hydrogen at ΔK < 21MPa√m. At ΔK > 21MPa√m, secondary cracks were observed in hydrogen environment. The differences in appearances of fracture surfaces in air and hydrogen are discussed.

  • 36.
    Stjernberg, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. LKAB.
    Olivas-Ogaz, M.A.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ion, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lindblom, B.
    LKAB.
    Laboratory scale study of the degradation of mullite/corundum refractories by reaction with alkali-doped deposit materials2013Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, nr 1, s. 791-800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Refractory bricks based on mullite and corundum, commonly used in rotary kilns for iron ore pellet production, and depositmaterial from an iron ore pellet production kiln, were used in laboratoryscale tests to investigate refractory/depositreactions and the infiltration of deposit components into the refractory bricks. The materials tested were in both monolithic form and in the form of powder. Alkali metal carbonates (containing sodium and potassium) were used as corrosive agents, to increase reaction kinetics. The morphological changes and active chemical reactions at the refractory/deposit interface in the samples were characterized by scanning electron microscopy. X-ray diffraction showed that alkali metals react with the mullite in the bricks, this being more pronounced in the case of sodium than potassium. Phases such as nepheline (Na2O·Al2O3·2SiO2), kalsilite and kaliophilite (both K2O·Al2O3·2SiO2), and leucite (K2O·Al2O3·4SiO2) were formed as a consequence of reactions between alkali metals and the refractory bricks. The formation of these phases causes volume expansions of between 20% and 25% in the brick materials, which accelerate degradation.

  • 37.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sefer, Birhan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Study of alpha case depth in Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V2013Ingår i: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, artikel-id 12002Konferensbidrag (Refereegranskat)
    Abstract [en]

    Titanium alloys, mostly Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) and Ti-6Al-4V (Ti-64) are used in aero engine applications, because they possess high specific strength. The future concept in designing aircraft engines results in higher pressure, which increases the efficiency of aircraft engines by achieving high thrust and lowering the fuel consumption. Nevertheless, higher pressure in the engine means increase of service temperature. These conditions enforce new requirements on the materials used for manufacturing the engine components (compressors). Ti-6242 is mostly used in compressors where the service temperature is in the range of 400-450°C. It is well known that titanium alloys above 480°C for longer service time have tendency to form a hard and brittle oxygen stabilized surface layer (α-case). This layer has impact on the mechanical properties of the surface, by lowering the tensile ductility and the fatigue resistance. Factors that contribute for growth of α-case are: presence of oxygen, exposure time, temperature and pressure. In order to extend the service temperature of titanium alloys, it is required to understand the formation of α-case at high temperatures for long exposure times. In the present study, isothermal oxidation experiments in air were performed on forged Ti-6242 alloy at 500°C and 593°C up to 500 hours. Similar studies were also performed on Ti-64 sheet at 593°C and 700°C. Alpha case depths for both alloys were quantified using metallography techniques and compared.

  • 38.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yao, Y.
    Klement, U.
    The effect of crystallographic orientation on solid metal induced embrittlement of Ti-8Al-1Mo-1V in contact with copper2013Ingår i: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, artikel-id 12011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Solid metal induced embrittlement (SMIE) occurs when a metal experiences tensile stress and is in contact with another solid metal with a lower melting temperature. SMIE is believed to be a combined action of surface self-diffusion of the embrittling species to the crack tip and adsorption of the embrittling species at the crack tip, which weakens the crack tip region. In the present study, both SMIE of the near alpha alloy Ti-8Al-1Mo-1V in contact with copper and its influence on crystallographic orientation have been studied. U-bend specimens coated with copper were heat treated at 480°C for 8 hours. One of the cracks was examined in detail using electron backscatter diffraction technique. A preferable crack path was found along high angle grain boundaries with grains oriented close to [0001] in the crack direction; this indicates that there is a connection between the SMIE crack characteristics and the crystallographic orientation.

  • 39.
    Stjernberg, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ion, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nordin, Lars-Olof
    LKAB.
    Lindblom, Bo
    LKAB.
    Odén, Magnus
    Linköping University, Division of Nanostructured Materials.
    Extended studies of degradation mechanisms in the refractory lining of a rotary kiln for iron ore pellet production2012Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, nr 8, s. 1519-1528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Changes, over a period of 8 years, in the chemical composition and morphology of deposit and lining materials in a production rotary kiln for iron ore pellet manufacture are described. The following have been studied: two types of refractory brick used as lining material; deposited chunk materials from the lining; the interaction zones between deposits and linings. Morphological changes at the deposit/lining interface, and the active chemical reactions, are established. Larger hematite grains in the deposit material (5–50 μm) primarily remain at the original deposit/lining interface. The remainder penetrates fissures, voids and brick joints, forms a laminar structure with corundum from the bricks, and migrates in grains in the lining material. Potassium penetrates more deeply into the bricks than hematite, resulting in the formation of kalsilite, leucite and potassium β-alumina, which contribute to degradation of the lining.

  • 40.
    Gaddam, Raghuveer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of hydrogen environment on the mechanical properties of cast and electron beam melted Ti-6Al-4V2012Ingår i: Ti-2011: proceedings of the 12th World Conference on Titanium, June 19-24, 2011, China National Convention Center (CNCC), Beijing / [ed] Lian Zhou, Beijing: Social Sciences Academic Press (China), 2012, Vol. 3, s. 1885-1888Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to save weight in a certain engine application the possibility of replacing the currently used material with cast Ti-6Al-4V is investigated here. The working environment for this particular engine part is pure hydrogen gas at high pressure. Therefore selected mechanical properties such as tensile and low cycle fatigue (LCF) in air and hydrogen atmosphere have been studied for cast Ti-6Al-4V. In addition to cast Ti-6Al-4Vt the corresponding mechanical properties of a more recently developed additive manufacturing method, electron beam melting (EBM), is also investigated in hydrogen and compared with cast Ti-6Al-4V. Cast Ti-6Al-4V showed lower yield strength and lower ultimate tensile strength in hydrogen compared with air. However, no significant change in the ductility was observed. The LCF was significantly reduced in the hydrogen atmosphere, mostly at high strain range (π 2%). The EBM Ti-6Al-4V in hydrogen showed higher yield strength, higher ultimate strength and higher ductility as well as improved fatigue life compared with cast Ti-6Al-4V under the same test conditions. Microstructural and fractographic characterization were also performed and the results are included.

  • 41.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Investigation of the influence of copper welding electrodes on Ti-8Al-1Mo-1V and Ti-6Al-2Sn-4Zr-2Mo with respect to solid metal induced embrittlement2012Ingår i: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Solid Metal Induced Embrittlement (SMIE) is caused by a specific combination of two solid metals in intimate contact. Cadmium, gold, silver and copper are known to cause SMIE in certain titanium alloys. Solid copper is used in welding electrodes and fixtures in various manufacturing processes for titanium parts within the aerospace industry. In the case of resistance welding, titanium alloys are in intimate contact with solid copper, since the electrodes resistively heat the titanium part under pressure during the welding process. No previous published work that investigates the risk of using copper electrodes for welding of titanium alloys is available in the literature, but an initial study using U-bend testing indicates that solid copper in contact with Ti-8Al-1V-1Mo and Ti-6Al-2Sn-4Zr-2Mo could lead to SMIE. Therefore, in the present study, resistance welded Ti-8Al-1V-1Mo and Ti-6Al-2Sn-4Zr-2Mo have been evaluated to investigate the influence of copper electrodes on these alloys. Furthermore, resistance welded specimens sputtered with copper and gold to promote SMIE have also been evaluated. No SMIE was found in the resistance welded specimens, which may be explained by the short interaction time that the copper electrodes are in intimate contact with the titanium alloy, and/or the magnitude of residual stresses after welding, which may be too low to initiate SMIE.

  • 42.
    Pederson, Robert
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gaddam, Raghuveer
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and mechanical behavior of Cast Ti-6Al-4V with addition of boron2012Ingår i: Central European Journal of Engineering, ISSN 1896-1541, E-ISSN 2081-9927, Vol. 2, nr 3, s. 347-357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of boron (between 0.06 and 0.11 wt%) on the microstructure, hardness and compression properties of cast Ti-6Al-4V was investigated. Compression properties were examined in the temperature range from room temperature to 1000ºC. It was found that the addition of boron refines the as-cast microstructure in terms of prior beta grain size and alpha colony size. This microstructural refinement led to an increase in compressive yield strength from room temperature up to 700ºC. Three different strain rates (0.001, 0.1 and 1 s-1) were evaluated during compression testing from which it was found that the compressive yield strength decreased with decreasing strain rate from 600ºC up to the beta transus temperature.

  • 43.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and mechanical properties of laser metal deposited Ti-6Al-4V2012Ingår i: Ti-2011: Proceedings of the 12th World Conference on Titanium, June 19 - 24, 2011, China National Convention Center (CNCC), Beijing / [ed] Lian Zhou, Beijing: Social Sciences Academic Press (China), 2012, Vol. 3, s. 1730-1734Konferensbidrag (Refereegranskat)
    Abstract [en]

    Laser metal deposition (LMD) is a near net shape manufacturing process in which the final shape of a part or component is built layer-by-layer. The energy of a laser beam is used to melt a wire of the selected pre-alloyed material onto a substrate or work piece. In the present study, the mechanical properties of laser metal deposited Ti-6Al-4V have been evaluated with respect to the yield strength, ultimate tensile strength, ductility and low cycle fatigue at room temperature and at 200°C. In addition, fractographic and metallographic studies were carried out in order to correlate the mechanical behaviour with grain morphology and microstructure. The yield strength, ultimate tensile strength, ductility and the low cycle fatigue properties of LMD material were all better than or equal to the corresponding mechanical properties of standard cast Ti-6Al-4V material. It was also found that defects, such as pores and surface irregularities, significantly reduce the fatigue life of LMD Ti-6Al-4V material, leading to premature fracture when present.

  • 44.
    Antti, Marta-Lena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Kero, Ida
    Cheng, Y-B
    Monash University, Melbourne, VIC.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Phase reactions in a hot pressed TiC/Si powder mixture2012Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 38, nr 3, s. 1999-2003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work investigated the possibility of producing dense Ti3SiC2 by hot pressing TiC/Si powders. A hot press with graphite heating elements was used for densification and the phase reactions of some hot pressed samples were further evaluated by pressureless heating in a dilatometer. The density and phase composition of the heat treated samples were evaluated using Archimedes principle and by x-ray diffractometry respectively. Hot pressing resulted in a low Ti3SiC2 yield; the main phases were TiC and TiSi2 regardless of starting powder composition, temperature, holding time or pressure. A second heating without pressure resulted in Ti3SiC2 formation, but only in samples initially hot pressed at 1300 °C or lower. At higher hot pressing temperatures, thin oxide layers on particle surfaces were locked into the structure. Acting as diffusion barriers, they prevented the Ti3SiC2 forming reaction. In hot pressed samples the density was significantly higher than in samples sintered without pressure

  • 45.
    Engström, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Córdoba, J.M.
    Instituto de Ciencia de Materiales de Sevilla, Código del Centro.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Synthesis of a TiCN – SiC polyhedron and elongated crystals nanopowder at low nitrogen concentration2012Ingår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 81, s. 148-150Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At room temperature diluted TiCl4 and CCl4 were reduced by sodium particles and mixed with a polycarbomethylsilane (PCS) solution to yield a precursor. It was dried and subsequently annealed at 1300 °C, 1400 °C and 1450 °C in a tube furnace using argon with 10 ppm N2. After the 1450 °C annealing a nanocrystalline powder of TiC0.5 N0.5–SiC polyhedron and elongated crystals was obtained. At the low nitrogen concentration during annealing a gradual nitration is proposed. It is promoted by carbon gaseous species, precursor oxidation, a sufficient temperature and a summarised nitrogen surplus compared to the titanium and carbon amount.

  • 46.
    Escalera, Edwin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ballem, Mohammed A.
    Nanostructured Materials, Department of Physics, Chemistry and Biology, Linköping University.
    Cordoba, José M.
    Nanostructured Materials, Department of Physics, Chemistry and Biology, Linköping University.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Odén, Magnus
    Synthesis of homogeneously dispersed cobalt nanoparticles in the pores of functionalized SBA-15 silica2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 221, s. 359-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cobalt nanoparticles were prepared at room temperature by reducing cobalt sulfate heptahydrate with sodium borohydride using functionalized SBA-15 mesoporous silica as a hard template. It was found that both external and internal fuctionalization of silica walls play a crucial role on the infiltration and reaction of the reagents in the silica framework. Subsequent heat treatment of the impregnated silica at 500 °C in air or nitrogen atmospheres leads to growth of crystals of the deposited cobalt and formation of cobalt oxide and cobalt nanoparticles, respectively. Dissolution of the silica template by NaOH resulted in well dispersed Co and Co3O4 nanoparticles ranging in size between 2 and 4 nm. The functionalization of the silica was studied by FTIR, N2-physisorption, and thermogravimetric techniques and the obtained nanoparticles were characterized by XRD, TEM and EDX analysis.

  • 47.
    Escalera, Edwin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Odén, Magnus
    Thermal treatment and phase formation in kaolinite and illite based clays from tropical regions of Bolivia2012Ingår i: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aim of this study was to compare the thermal behaviour of clays containing illite and kaolinite in various proportions. The clays contained small amounts of K and Fe, which act as fluxing agents. In order to investigate the phase formations during heating, the samples were examined in a differential scanning calorimeter at temperatures up to 1300°C. The thermal expansion of the samples was determined by dilatometer measurements from room temperature up to 1150°C. Phases were identified using x-ray diffraction and scanning electron microscopy. In all samples, most of the kaolinite was transformed into metakaolinite during heating up to 650°C, while illite remained unchanged up to 950°C. There was no influence of K and Fe on dehydroxylation. Metakaolinite formed at temperatures above 950°C leading to a Si-Al spinel. Furthermore, mullite was formed in the temperature interval 1050-1150°C. In this temperature range, the mechanism of mullite formation depended on the amount of K and Fe in the samples, changing the temperature of formation of mullite. It was observed by x-ray diffraction that most of the illite was transformed into a Si-Al spinel phase at 1050°C, and during further heating transformed into mullite. An increased amount of illite in the clays slightly decreased the melting temperature. The dilatometer measurements showed expansion and shrinkage for the dehydroxylation and spinel-phase formation, respectively.

  • 48.
    Stjernberg, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ion, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lindblom, B.
    LKAB.
    Lab scale study of the depletion of mullite/corundum-based refractories trough reaction with scaffold materials2011Ingår i: IOP Conference Series: Materials Science and Engineering: Symposium 16, 2011 (222001-222031) Innovation in Refractories and Traditional Ceramics, IOP Publishing Ltd , 2011, Vol. 18, artikel-id 222004Konferensbidrag (Refereegranskat)
    Abstract [en]

    To investigate the mechanisms underlying the depletion of mullite/corundum-based refractory bricks used in rotary kilns for iron ore pellet production, the reaction mechanisms between scaffold material and refractory bricks have been studied on the laboratory-scale. Alkali additions were used to enhance the reaction rates between the materials. The morphological changes and active chemical reactions at the refractory/scaffold material interface in the samples were characterized using scanning electron microscopy (SEM), thermal analysis (TA) and X-ray diffraction (XRD). No reaction products of alkali and hematite (Fe2O3) were detected; however, alkali dissolves the mullite in the bricks. Phases such as nepheline (Na2OAl2O32SiO2), kalsilite (K2OAl2O32SiO2), leucite (K2OAl2O34SiO2) and potassium β-alumina (K2O11Al2O3) were formed as a consequence of reactions between alkali and the bricks.

  • 49. Kero, Ida
    et al.
    Tegman, Ragnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Phase reactions associated with the formation of Ti3SiC2 from TiC/Si powders2011Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 37, nr 7, s. 2615-2619Artikel i tidskrift (Refereegranskat)
  • 50.
    Åkerfeldt, Pia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Solid metal induced embrittlement of titanium alloys in contact with copper2011Ingår i: Ti-2011: Proceedings of the 12th World Conference on Titanium, June 19 - 24, 2011, China National Convention Center (CNCC), Beijing / [ed] Lian Zhou, Beijing: Social Sciences Academic Press (China), 2011, Vol. 3, s. 1868-1871Konferensbidrag (Refereegranskat)
    Abstract [en]

    Solid Metal Induced Embrittlement (SMIE) is caused by a specific combination of a susceptible alloy, tensile stress and a solid metal. Solid copper is commonly used in various manufacturing processes, e.g. in welding electrodes and clamping fixtures, during the manufacturing and handling of titanium alloy parts for the aerospace industry. An initial study indicated that copper in contact with titanium could lead to SMIE and was the reason for initiating the current work. Three titanium alloys; Ti-8Al-1Mo-1V, Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V, have been evaluated with respect to SMIE in contact with copper. The evaluation was carried out by using a modified U-bend test method adapted from SAE ARP 1795, a standard used for Stress-Corrosion Cracking (SCO evaluation of titanium alloys in contact with cleaning solutions. Gold was also investigated in order to validate the reliability of the test method since it has been reported that titanium alloys undergo SMIE in contact with solid gold. The results show that both Ti-8Al-1Mo-1V and Ti-6Al-2Sn-4Zr-2Mo are susceptible to SMIE in contact with copper whereas SMIE was not observed with Ti-6Al-4V. ----------------------------------------------------------------------------------------------------------------------------------------------------------------

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