Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore
doi:10.3850/978-981-18-6021-8_OR-01-0242
Additive Manufacturing of Titanium Aluminides for Aircraft Engine Applications
1Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
2Anisotropic Design & Additive Manufacturing Research Center, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
3Department of Environmental Materials Engineering, Institute of Niihama National College of Technology, 7-1, Yagumo-cho Niihama, Ehime, 792-8580, Japan
4Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
ABSTRACT
Titanium aluminide (TiAl) alloys have been widely used for low pressure turbine blades of aircraft engine due to their excellent strength-to-weight ratio and good oxidation resistance. However, contamination from crucible and oxidation during precision investment casting are hard to avoid. Recently, electron beam powder bed fusion (EB-PBF), one of the additive manufacturing processes, has attracted much attention to fabricate TiAl low pressure turbine blades since the process can build 3D objects with arbitrary shape while suppressing contamination and oxidation. It is also noted that microstructure and mechanical properties of TiAl alloys can also be controlled by EB-PBF process. For instance, Ti-48Al-2Cr-2Nb (at.%) alloys mainly consist of the α2 and γ phases with the D019 and L10 structures, respectively. The microstructure depends strongly on an input energy density depending on the process parameters such as beam current, scanning speed and scanning pitch. At appropriate energy densities, peculiar banded structure composed of fine duplex structure and a chain of equiaxed γ grains (γband) is formed, which results from the temperature distribution around a melt pool and repeated powder feed/fusion cycles during the EB-PBF process. The mechanical properties of TiAl alloys fabricated by EB-PBF are closely related to the microstructure. If the angle between a tensile axis and the γ bands is 45°, large elongation can be obtained at room temperature, which is favorable for the practical applications. This is because the soft γ phase is parallel to maximum shear stress plane. High temperature strength, fatigue and creep properties of the alloys also depend on the microstructure. However, since the banded structure is so sensitive to the energy densities, microstructure of the large product varies from area to area. In the present study, a new scan strategy of EB-PBF is proposed to obtain TiAl alloys with homogenous banded structure throughout the product.
Keywords: Additive manufacturing, Titanium aluminides, Microstructure control, Scan strategy.
1Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
2Anisotropic Design & Additive Manufacturing Research Center, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
3Department of Environmental Materials Engineering, Institute of Niihama National College of Technology, 7-1, Yagumo-cho Niihama, Ehime, 792-8580, Japan
4Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
ABSTRACT
Titanium aluminide (TiAl) alloys have been widely used for low pressure turbine blades of aircraft engine due to their excellent strength-to-weight ratio and good oxidation resistance. However, contamination from crucible and oxidation during precision investment casting are hard to avoid. Recently, electron beam powder bed fusion (EB-PBF), one of the additive manufacturing processes, has attracted much attention to fabricate TiAl low pressure turbine blades since the process can build 3D objects with arbitrary shape while suppressing contamination and oxidation. It is also noted that microstructure and mechanical properties of TiAl alloys can also be controlled by EB-PBF process. For instance, Ti-48Al-2Cr-2Nb (at.%) alloys mainly consist of the α2 and γ phases with the D019 and L10 structures, respectively. The microstructure depends strongly on an input energy density depending on the process parameters such as beam current, scanning speed and scanning pitch. At appropriate energy densities, peculiar banded structure composed of fine duplex structure and a chain of equiaxed γ grains (γband) is formed, which results from the temperature distribution around a melt pool and repeated powder feed/fusion cycles during the EB-PBF process. The mechanical properties of TiAl alloys fabricated by EB-PBF are closely related to the microstructure. If the angle between a tensile axis and the γ bands is 45°, large elongation can be obtained at room temperature, which is favorable for the practical applications. This is because the soft γ phase is parallel to maximum shear stress plane. High temperature strength, fatigue and creep properties of the alloys also depend on the microstructure. However, since the banded structure is so sensitive to the energy densities, microstructure of the large product varies from area to area. In the present study, a new scan strategy of EB-PBF is proposed to obtain TiAl alloys with homogenous banded structure throughout the product.
Keywords: Additive manufacturing, Titanium aluminides, Microstructure control, Scan strategy.
