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  • 51.
    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.

  • 52.
    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.

  • 53.
    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.

  • 54.
    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.

  • 55.
    Stjernberg, Jesper
    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.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindblom, B.
    LKAB.
    Lab scale study of the depletion of mullite/corundum-based refractories trough reaction with scaffold materials2011In: IOP Conference Series: Materials Science and Engineering: Symposium 16, 2011 (222001-222031) Innovation in Refractories and Traditional Ceramics, IOP Publishing Ltd , 2011, Vol. 18, article id 222004Conference paper (Refereed)
    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.

  • 56.
    Stjernberg, Jesper
    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.
    Nordin, L-O
    LKAB Research and Development, Metlab.
    Odén, Magnus
    Linköping University, Division of Nanostructured Materials.
    Study of the degradation process of refractory bricks in rotary kilns2008In: Global roadmap for ceramics & ICC2 proceedings: 2nd International Congress on Ceramics ; June 29 - July 4, 2008, Verona, Italy / [ed] Alida Bellosi, Faenza: Institute of Science and Technology for Ceramics , 2008Conference paper (Refereed)
    Abstract [en]

    Iron ore pellets are commonly sintered in a kiln insulated with bricks, which wear and need to be replaced regularly. It is desirable to increase the lifetime of those bricks. Slag/brick compatibility tests have been performed in a laboratory furnace. Slag collected from a production kiln, three commercial bricks and additions of alkali were used. Alkali dissolves the mullite in the bricks, and form the phases nepheline and kalsilite. Characterization of the microstructure showed that the degradation of the bricks was enhanced by increased temperature and amount of alkali. The slag penetration depth is more affected by increased temperature than increased dwell time.

  • 57. Stjernberg, Jesper
    et al.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Odén, Magnus
    Linköpings universitet.
    Nordin, Lars-Olof
    LKAB.
    Degradation of refractory bricks used as thermal insulation in rotary kilns for iron ore pellet production: degradation of refractory bricks used as thermal insulation in rotary kilns2009In: International Journal of Applied Ceramic Technology, ISSN 1546-542X, Vol. 6, no 6, p. 717-726Article in journal (Refereed)
    Abstract [en]

    Degradation of bricks in an iron ore pellet producing kiln has been investigated. Lab-scale tests of brick/slag interaction performed under different temperatures, atmospheres, and alkali additions show that addition of alkali dissolves the mullite in the brick and leads to formation of the phase nepheline (Na2O·Al2O3·2SiO2). At a high temperature, the grain boundary where nepheline is formed disintegrates due to volume expansion. At increased temperature, the nepheline transforms to an amorphous phase. Thus, a wear mechanism is proposed in the kiln using these bricks that involves these chemical reactions in combination with erosion by the continuously flowing slag.

  • 58.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ion, John
    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.
    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 production2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 8, p. 1519-1528Article in journal (Refereed)
    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.

  • 59.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindblom, B.
    LKAB.
    Wikström, J.
    LKAB.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Odén, Magnus
    Microstructural characterization of alkali metal mediated high temperature reactions in mullite based refractories2010In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 36, no 2, p. 733-740Article in journal (Refereed)
    Abstract [en]

    Two types of refractory bricks were used in reaction tests with slag from a production kiln for iron ore pellet production. Electron microscopy was used to characterize morphological changes at the slag/brick interface and active chemical reactions. Phases such as kalsilite, nepheline and potassium β-alumina form, in a layered structure, as a consequence of alkali metals migration in the brick. Larger hematite grains (50-100 μm) in the slag remain at the original slag/brick interface, while smaller grains dissolve and move through the partly dissolved brick bulk, and forms micrometer sized needle shaped crystals deeper in the lining material. Thermodynamic simulations predict the formation of a solid solution between hematite and corundum which is also observed in the reaction zone after extended time periods.

  • 60.
    Stjernberg, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. LKAB.
    Olivas-Ogaz, M.A.
    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.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindblom, B.
    LKAB.
    Laboratory scale study of the degradation of mullite/corundum refractories by reaction with alkali-doped deposit materials2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 1, p. 791-800Article in journal (Refereed)
    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.

  • 61.
    Stöckel, Birgit
    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.
    Norberg, Anders
    Umeå universitet.
    Ett pilotförsök med time-based blended learning i basårskontext2014In: NU 2014: Umeå 8-10 oktober : abstracts, Umeå: Umeå universitet. Pedagogiska institutionen , 2014, p. 115-Conference paper (Refereed)
  • 62.
    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

  • 63.
    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.

  • 64.
    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.

  • 65.
    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.

  • 66.
    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.

  • 67.
    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. ----------------------------------------------------------------------------------------------------------------------------------------------------------------

  • 68.
    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.

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