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  • 1.
    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.

  • 2.
    Karimi, Paria
    et al.
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Sadeghi, Esmaeil
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ålgårdh, Joakim
    Department of Engineering Science, University West, Trollhättan, Sweden. Powder Materials & Additive Manufacturing, Swerea KIMAB AB, Kista, Sweden.
    Andersson, Joel
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Influence of successive thermal cycling on microstructure evolution of EBM-manufactured alloy 718 in track-by-track and layer-by-layer design2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, p. 427-441Article in journal (Refereed)
    Abstract [en]

    Successive thermal cycling (STC) during multi-track and multi-layer manufacturing of Alloy 718 using electron beam melting (EBM) process leads to a microstructure with a high degree of complexity. In the present study, a detailed microstructural study of EBM-manufactured Alloy 718 was conducted by producing samples in shapes from one single track and single wall to 3D samples with maximum 10 longitudinal tracks and 50 vertical layers. The relationship between STC, solidification microstructure, interdendritic segregation, phase precipitation (MC, δ-phase), and hardness was investigated. Cooling rates (liquid-to-solid and solid-to-solid state) was estimated by measuring primary dendrite arm spacing (PDAS) and showed an increased cooling rate at the bottom compared to the top of the multi-layer samples. Thus, microstructure gradient was identified along the build direction. Moreover, extensive formation of solidification micro-constituents including MC-type carbides, induced by micro-segregation, was observed in all the samples. The electron backscatter diffraction (EBSD) technique showed a high textured structure in 〈001〉 direction with a few grains misoriented at the surface of all samples. Finer microstructure and possibility of more γ″ phase precipitation at the bottom of the samples resulted in slightly higher (~11%) hardness values compared to top of the samples.

  • 3.
    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.

  • 4.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Division of Welding Technology, University West, Trollhättan .
    Åkerfeldt, Pia
    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 characterisation of Ti-6Al-4V from different additive manufacturing processes2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 258, article id 012007Article in journal (Refereed)
    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.

  • 5.
    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].

  • 6.
    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.

  • 7.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Additive Manufacturing of Ti-6Al-4V: Relationship between Microstructure, Defects and Mechanical Properties2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Additive manufacturing (AM) is a relatively new technology that is labelled to be innovative, disruptive, near-net shaping, enabling manufacturing of complex and customised products, for limitless number of applications, directly from the CAD model into real physical parts. For titanium alloys in aerospace applications, AM moreover stands for a reduced material cost, but also for large challenges when considering consistency and qualification of material properties and components in serial production. In the AM process the feedstock material is melted by a heat source that moves according to a building sequence defined by the CAD model. Layer-by-layer the material solidifies into the wanted shape and accordingly the microstructure forms,which determines the average mechanical properties of the manufactured component. However, even if the AM process seems to be very straight forward, the prediction of mechanical and metallurgical properties is complex, partly because of its building in layer nature which generates a complex thermal history dictating the mechanical properties, and partly because of the number of parameters involved during the AM process itself. The objective of the present work was to increase the fundamental understanding of the relationship between microstructure, defects and mechanicalproperties of AM:ed Ti-6Al-4V. Three AM techniques were investigated, namely laser metal-wire deposition (LMwD), electron beam melting (EBM), and gas tungsten arc welding (GTAW) wire feed AM, with the main focus on LMwD. The different techniques were evaluated with regard to microstructure and tensile and fatigue properties. In addition, the EBM Ti-6Al-4V was tested in a hydrogen atmosphere to simulate the working environment for a certain engine application. One of the core findings in the present work was that AM:ed Ti-6Al-4V exhibited a columnar microstructure with elongated prior beta grains growing through several layers following the temperature gradient direction in the built material. To cover the different characteristics of the columnar microstructure, the mechanical properties were evaluated in two orientations of the built Ti-6Al-4V. The mechanical properties, both static and dynamic, were found to be anisotropic, which was further evaluated indetail with respect to the microstructure evolution and defects generated by the AM process. Among the results, when different process conditions were tested, it was concluded that the thickness of the grain boundary alpha along the prior beta grain boundary did not influence the level of anisotropy. However, the prior beta grain boundary was observed to be the weakest microconstituent when the load was applied perpendicular to its prevalence in both tensile and LCF testing. In order to get a better understanding of how the columnar microstructure influences the fatigue properties, the fatigue crack propagation characteristics were investigated with respect to the columnar prior beta grains and crystal orientation. An extensive fractographic study was carried out on all tested specimens. Lack of fusion (LoF) defects were concluded to be the individually most detrimental type of defect to the material properties. The influence of the LoF defects was further concluded to be very dependent on its prevalence in relation to the loading direction; the largest impact on the fatigue life was observed when the LoF defect wasperpendicular to the loading direction. Finally, a part of the aim of the present work was to support the development of a microstructure model that will be implemented in a thermo-mechanical model when simulating AM of Ti-6Al-4V. In order to validate the material model developed, the alpha lath thickness and the fraction of grain boundary alpha were quantified atspecific locations in single and multiple bead walls of GTAW wire feed AM:ed Ti-6Al-4V and compared with the results of the simulated AM process of Ti-6Al-4V.

  • 8.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solid metal induced embrittlement of titanium alloys2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Titanium alloys were for a time believed to be highly resistant to environmentally assisted cracking because of their ability to form a protective oxide film on the surface. Their resistance can still be considered to be high, but when cracking resistance was originally defined to ensure reliable functionality of fracture-critical components, certain conditions that promote cracking were discovered. One of the environmental assisted cracking processes relevant to titanium alloys is solid metal induced embrittlement (SMIE). SMIE refers to the embrittlement that occurs in normally ductile materials under tensile stress in contact with solid metals with a lower melting temperature than titanium. Even though failures resulting from SMIE are rare, they do occur, partly because the industry is not aware of conditions under which SMIE may exist. Titanium alloys are frequently used in the aerospace industry where solid copper contact can be found in for instance, welding electrodes and fixtures in various manufacturing processes. The main scope of the present work has been to clarify the effect of copper in contact with titanium alloys with respect to SMIE and further to increase the understanding of SMIE. Three titanium alloys: Ti-8Al-1V-1Mo, Ti-6Al- 2Sn-4Zr-2Mo and Ti-6Al-4V have been evaluated in contact with copper, and in contact with gold for comparison.In order to be able to evaluate SMIE, a U-bend test method adapted from an aerospace recommended practice for stress-corrosion cracking (ARP SAE 1795A) was modified for SMIE evaluation. The acceptability of the test method was successfully established by using reference specimens that were intended to crack (or not to crack) when in contact with the embrittling environment. The results of the SMIE tests show that both Ti-8Al-1V-1Mo and Ti-6Al-2Sn-4Zr-2Mo are susceptible to SMIE in contact with copper and gold, whilst no SMIE was observed with Ti-6Al-4V. Based on these findings it is suggested that the SMIE susceptibility of titanium alloys is dependent on alloy composition. Furthermore, resistance welded Ti-8Al-1V-1Mo and Ti-6Al-2Sn-4Zr-2Mo were evaluated to investigate whether the presence of copper electrodes, (the welding operation itself) could lead to SMIE. No SMIE was found in the resistance welded specimens, which may be explained by the short time that the copper electrodes were in intimate contact with the titanium alloy, the magnitude of residual stresses after welding, or both, which were too low to initiate SMIE. In order to obtain a better understanding of the crack path characteristics and the mechanisms involved, one U-bent specimen showing SMIE (Ti-8Al-1V-1Mo with copper) was selected for further examination using electron backscatter diffraction (EBSD). The EBSD results indicated a preferable crack propagation path along high angle grain boundaries, which supports the suggested adsorption mechanism of the embrittling species at the crack tip. A tendency for favourable crack growth along grain boundaries adjacent to grains oriented close to [0001] in the crack direction could also be seen, which indicates that there is a connection between the SMIE crack characteristics and the crystallographic orientation.

  • 9.
    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

  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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.

  • 14.
    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. ----------------------------------------------------------------------------------------------------------------------------------------------------------------

  • 15.
    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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