Effect of building direction on the microstructure and tensile properties of Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting

• Published in: Additive manufacturing Vol. 13; pp. 61 - 70
• Main Authors: Todai, Mitsuharu, Nakano, Takayoshi, Liu, Tianqi, Yasuda, Hiroyuki Y., Hagihara, Koji, Cho, Ken, Ueda, Minoru, Takeyama, Masao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2017
• Subjects: Additive manufacturing; Electron beam melting (EBM); Microstructure; Tensile test; Titanium aluminides; Titanium aluminides; Additive manufacturing; Microstructure; Tensile test; Electron beam melting (EBM)
• ISSN: 2214-8604; 2214-7810
• DOI: 10.1016/j.addma.2016.11.001

[Display omitted] •Control of microstructure in a TiAl alloy was conducted by electron beam melting (82/85).•An unique layered microstructure was created by the proposed EBM process (74/85).•The room temperature ductility was greater than 2% under an appropriate condition (83/85).•As-EBM specimens exhibited high yield strength and good ductility at 800°C (76/85). This paper clarified a novel strategy to improve the tensile properties of the Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting (EBM), via the finding of the development of unique layered microstructure composed of duplex-like fine grains layers and coarser γ grains layers. It was clarified that the mechanical properties of the alloy fabricated by EBM can be controlled by varying an angle θ between EBM-building directions and stress loading direction. At room temperature, the yield strength exhibits high values more than 550MPa at all the loading orientations investigated (θ=0, 45 and 90°). In addition, the elongation at θ=45° was surprisingly larger than 2%, owing to the development of this unique layered microstructure. The anisotropy of the yield strength decreased with increasing temperature. All the examined alloys exhibited a brittle-ductile transition temperature of approximately 750°C and the yield strength and tensile elongation at 800°C were over 350MPa and 40%, respectively. By the detailed observation of the microstructure, the formation mechanism of the unique layered microstructure was found to be closely related to the repeated local heat treatment effect during the EBM process, and thus its control is further possible by the tuning-up of the process parameters. The results demonstrate that the EBM process enables not only the fabrication of TiAl products with complex shape but also the control of the tensile properties associated with the peculiar microstructure formed during the process.