Change search
Refine search result
1 - 29 of 29
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science. 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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mateo, Antonio
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Oxidation behavior of Ti6Al4V alloy exposed to isothermal and cyclic thermal treatments2017In: METAL 2017: 26th International Conference on Metallurgy and Materials, Conference Proceedings, Ostrava: TANGER Ltd. , 2017, p. 1573-1579Conference paper (Refereed)
    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.

  • 2.
    Gaddam, Raghuveer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of alpha–case layer on the low cycle fatigue properties of Ti–6Al–2Sn–4Zr–2Mo alloy2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 599, p. 51-56Article in journal (Refereed)
    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.

  • 3. Gaddam, Raghuveer
    et al.
    Hörnqvist, M.
    Department of Applied Physics, Chalmers University of Technology.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of High-pressure gaseous Hydrogen on the low-cycle fatigue and fatigue crack growth properties of a cast titanium alloy2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 612, p. 354-362Article in journal (Refereed)
    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

  • 4.
    Gaddam, Raghuveer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hörnqvist, Magnus
    GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fatigue crack growth behaviour of forged Ti-6Al-4V in gaseous hydrogen2014In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 78, p. 378-383Article in journal (Refereed)
    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.

  • 5.
    Gaddam, Raghuveer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hörnqvist, Magnus
    GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of hydrogen environment on fatigue crack growth in forged Ti-6Al-4V: fractographic analysis2013In: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, article id 1210Conference paper (Refereed)
    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.

  • 6. Gaddam, Raghuveer
    et al.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oxidation and alpha–case formation in Ti–6Al–2Sn–4Zr–2Mo alloy2015In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 99, p. 166-174Article in journal (Refereed)
    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.

  • 7.
    Gaddam, Raghuveer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Study of alpha case depth in Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V2013In: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, article id 12002Conference paper (Refereed)
    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.

  • 8.
    Gaddam, Raghuveer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of hydrogen environment on the mechanical properties of cast and electron beam melted Ti-6Al-4V2012In: 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, p. 1885-1888Conference paper (Refereed)
    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.

  • 9.
    Lundbäck, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pederson, Robert
    Hörnqvist Colliander, Magnus
    GKN Aerospace Engine Systems, 461 81 Trollhättan.
    Brice, Craig
    NASA Langley Research Center, Hampton, Virginia USA.
    Steuwer, Axel
    NMMU, Gardham Av, 6031 Port Elizabeth, South Africa.
    Heralic, Almir
    GKN Aerospace Engine Systems, 461 81 Trollhättan.
    Buslaps, Thomas
    ID15A, European Synchrotron Radiation Facility ESRF, Grenoble, France.
    Lindgren, Lars-Erik
    Modeling and Experimental Measurement with Synchrotron Radiation of Residual Stresses in Laser Metal Deposited Ti-6Al-4V2016In: Proceedings of the 13th World Conference on Titanium, 2016, p. 1279-1282Conference paper (Refereed)
    Abstract [en]

    There are many challenges in producing aerospace components by additive manufacturing (AM). One of them is to keep the residual stresses and deformations to a minimum. Another one is to achieve the desired material properties in the final component. A computer model can be of great assistance when trying to reduce the negative effects of the manufacturing process. In this work a finite element model is used to predict the thermo-mechanical response during the AM-process. This work features a physically based plasticity model coupled with a microstructure evolution model for the titanium alloy Ti -6Al-4V. Residual stresses in AM components were measured non-destructively using high-energy synchrotron X-ray diffraction on beam line ID15A at the ESRF, Grenoble. The results are compared with FE model predictions of residual stresses. During the process, temperatures and deformations was continuously measured. The measured and computed thermal history agrees well. The result with respect to the deformations agrees well qualitatively. Meaning that the change in deformation in each sequence is well predicted but there is a systematic error that is summing so that the quantitative agreement is lost.

  • 10.
    Lundbäck, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hörnqvist, Magnus
    GKN Aerospace Engine Systems.
    Brice, Craig
    NASA Langley Research Center, Hampton.
    Steuwer, Axel
    MAX-lab, Lund University.
    Heralic, Almir
    GKN Aerospace Engine Systems Sweden.
    Buslaps, Thomas
    ID15A, European Synchrotron Radiation Facility ESRF, 38042 Grenoble.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modelling and Simulation of Metal Deposition on a Ti-6al-4v Plate2015Conference paper (Other academic)
    Abstract [en]

    There are many challenges in producing aerospace components by metal deposition (MD). One of them is to keep the residual stresses and deformations to a minimum. Anotherone is to achieve the desired material properties in the final component. A computer model can be of great assistance when trying to reduce the negative effects of the manufacturing process. In this work a finite element model is used to predict the thermo-mechanical response during the MD-process. This work features a pysically based plasticity model coupled with a microstructure evolution model for the titanium alloy Ti-6Al-4V. A thermally driven microstructure model is used to derive the evolution of the non-equilibrium compositions of α-phases and β-phase. Addition of material is done by activation of elements. The method is taking large deformations into consideration and adjusts the shape and position of the activated elements. This is particularilly important when adding material onto thin and flexible structures. The FE-model can be used to evaluate the effect of different welding sequenses. Validation of the model is performed by comparing measured deformations, strains, residual stresses and temperatures with the computed result. The deformations, strains and temepratures are measured during the process. The deformations are measured with a LVDT-gauge at one location. The strains are measured with a strain gauge at the same location as the deformations. The temperature is measured at five locations, close to the weld and with an increasing distance of one millimeter between each thermo couple. The residual stresses in MD component were measured non-destructively using high-energy synchrotron X-ray diffraction on beam line ID15A at the ESRF, Grenoble.

  • 11.
    Murgau, C Charles
    et al.
    University West, Trollhättan.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A model for Ti–6Al–4V microstructure evolution for arbitrary temperature changes2012In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 20, no 5, article id 055006Article in journal (Refereed)
    Abstract [en]

    This paper presents a microstructure model for the titanium alloy Ti–6Al–4V designed to be used in coupled thermo-metallurgical-mechanical simulations of, e.g., welding processes. The microstructure evolution is increasingly taken into consideration in analyses of manufacturing processes since it directly affects the mechanical properties. Thermally driven phase evolutions are accounted for in the model. A state variable approach is adopted to represent the microstructure with the objective to integrate the microstructure changes with a thermo-mechanical model of manufacturing process simulation such as welding. The model is calibrated using the literature data and also validated against a cyclic temperature history during multi-pass welding.

  • 12.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pederson, Robert
    Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Puyoo, Geraldine
    GKN-Aerospace Engine Systems.
    Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography2018In: Aeronautics and Aerospace Open Access Journal, ISSN 2576-4500, Vol. 2, no 3, p. 139-145Article in journal (Refereed)
    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.

  • 13.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    University West, Trollhättan, Sweden.
    Bjerkén, Christina
    Malmö University, Sweden.
    Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction2018In: Additive Manufacturing, ISSN 2214-8604, Vol. 23, p. 225-234Article in journal (Refereed)
    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].

  • 14.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Division of Welding Technology, University West, Trollhättan 461 32, Sweden.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microstructural characterization and comparison of Ti-6Al-4V manufactured with different additive manufacturing processes2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 143, no SI, p. 68-75Article in journal (Refereed)
    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.

  • 15.
    Pederson, Robert
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gaddam, Raghuveer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microstructure and mechanical behavior of Cast Ti-6Al-4V with addition of boron2012In: Central European Journal of Engineering, ISSN 1896-1541, E-ISSN 2081-9927, Vol. 2, no 3, p. 347-357Article in journal (Refereed)
    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.

  • 16.
    Pederson, Robert
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Niklasson, F.
    Volvo Aero.
    Skystedt, F.
    Volvo Aero Corporation, Materials Technology.
    Warren, R.
    University of Malmö, Department of Technology and Society.
    Microstructure and mechanical properties of friction- and electron beam welded Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo2012In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 552, p. 555-565Article in journal (Refereed)
    Abstract [en]

    This work presents mechanical data and microstructural characterization of friction welded (FRW) and electron beam welded (EBW) post weld heat treated (PWHT) specimens of Ti-6Al-2Sn-4Zr-6Mo and Ti-6Al-4 V. PWHT Ti6246/Ti6246 welds and Ti64/Ti6246 welds were evaluated with tensile-, creep-, Charpy-V, and microhardness tests. The PWHT treatments were 593 °C/2 h, 640 °C/2 h and 704 °C/2 h, respectively. The microstructure of the different weld types and alloy combinations where examined and characterized using optical microscope and SEM.Tensile strength and yield strength were within specification for both material combinations. The elongation for Ti6246 welded to Ti6246 is below specification. Only small variations in tensile properties were found for the different PWHTs. Fracture occurred in base material of the Ti64 alloy for the combination of Ti64 welded to Ti6246.Charpy-V tests shows that the welds are more brittle compared with the base material. The largest difference was found in Ti6246 welded to Ti6246.No significant variation in creep properties for the different PWHTs has been found. Ti64 welded to Ti6246 shows poor creep properties due to the high testing temperature for the Ti64 alloy. Ti6246 welded to Ti6246 shows good creep properties compared to the base material.The general trend for the weld microhardness was a decreasing hardness with increasing PWHT temperature. One exception though was the FRW Ti64/Ti6246 combination, were the hardness of the Ti6246 side of the HAZ, close to the interface between the two alloys, was highest after a PWHT temperature of 593 °C, then decreasing in hardness for 640 °C, not PWHT and being least hard for the PWHT temperature of 704 °C. The hardness of the Ti64 base material showed no decrease after the PWHTs, but the hardness of the Ti6246 bulk material decreased after PWHT at 704 °C.

  • 17.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Surface and Corrosion Science, KTH Royal Institute of Technology.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research and Technology Centre, GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions2017In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, no 4, p. 394-407Article in journal (Refereed)
    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.

  • 18.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gaddam, Raghuveer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. GKN Aerospace Engine Systems Sweden.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Study of the Alpha-Case Layer in Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V by Electron Probe Micro Analysis2014Conference paper (Refereed)
    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.

  • 19.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical milling effect on the low cycle fatigue properties of cast Ti-6Al-2Sn-4Zr-2Mo alloy2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, no 1, p. 193-202Article in journal (Refereed)
    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.

  • 20.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Evaluation of the bulk and alpha-case properties in Ti-6Al-4V at micro- and nano-metric length scale2016In: 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, p. 1619-1624, article id 271Conference paper (Refereed)
    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.

  • 21.
    Singh, Gaurav
    et al.
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Satyanarayana, D.V.V.
    Defence Metallurgical Research Laboratory, Hyderabad.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Datta, Ranjan
    International Centre for Materials Science, JNCASR, Jakkur PO, Bangalore.
    Ramamurty, Upadrasta
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Enhancement in creep resistance of Ti-6Al-4 V alloy due to Boron addition2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 597, p. 194-203Article in journal (Refereed)
    Abstract [en]

    The addition of B, up to about 0.1 wt.%, to Ti-6Al-4 V reduces its as-cast grain and colony sizes by an order of magnitude. In this paper, the creep resistance of this alloy modified with 0.06 and 0.11 wt.% B additions was investigated in the temperature range of 475–550 °C and compared with that of 0B alloy. Conventional dead-weight creep tests as well as stress relaxation tests were employed for this purpose. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the alloy with 0.11 wt.% B was found to be an order of magnitude lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces – a direct consequence of the microstructural refinement that occurs with the B addition – that provide resistance to dislocation motion

  • 22.
    Singha, Gaurav
    et al.
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Gaddam, Raghuveer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Petley, Vijay
    Gas Turbine Research Establishment, DRDO, Bangalore.
    Datta, Ranjan
    International Centre for Materials Science, JNCASR, Jakkur PO, Bangalore.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ramamurtya, Upadrasta
    Department of Materials Engineering, Indian Institute of Science, Bangalore.
    Strain-controlled fatigue in B-modified Ti-6Al-4V alloys2013In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, no 9, p. 698-701Article in journal (Refereed)
    Abstract [en]

    The strain-controlled fatigue behaviour of Ti-6Al-4V alloy with up to 0.11 wt.% B addition was investigated. Results show significant softening when the strain amplitudes, ΔεT/2, are ⩾0.75%. B addition was found to improve the fatigue life for ΔεT/2 ⩽ 0.75% as it corresponds to the elastic regime and hence strength dominated. At ΔεT/2 = 1%, in contrast, the base alloy exhibits higher life as TiB particle cracking due to strain incompatibility renders easy crack nucleation in the B-modified alloys.

  • 23.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of microstructure on mechanical properties of laser metal wire-deposited Ti-6Al-4V2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, p. 428-437Article in journal (Refereed)
    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

  • 24.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Electron backscatter diffraction characterization of fatigue crack growth in laser metal wire deposited Ti-6Al-4V2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 245-256Article in journal (Refereed)
    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.

  • 25.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A fractographic study exploring the relationship between the low cycle fatigue and metallurgical properties of laser metal wire deposited Ti-6Al-4V2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, p. 245-256Article in journal (Refereed)
    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.

  • 26.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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 embrittlement2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    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.

  • 27.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microstructure and mechanical properties of laser metal deposited Ti-6Al-4V2012In: 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, p. 1730-1734Conference paper (Refereed)
    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.

  • 28.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solid metal induced embrittlement of titanium alloys in contact with copper2011In: 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, p. 1868-1871Conference paper (Refereed)
    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. ----------------------------------------------------------------------------------------------------------------------------------------------------------------

  • 29.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yao, Y.
    Klement, U.
    The effect of crystallographic orientation on solid metal induced embrittlement of Ti-8Al-1Mo-1V in contact with copper2013In: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, article id 12011Conference paper (Refereed)
    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.

1 - 29 of 29
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf