Influence of unique layered microstructure on fatigue properties of Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting

Ken Cho, Ryota Kobayashi, Jong Yeong Oh, Hiroyuki Y. Yasuda, Mitsuharu Todai, Takayoshi Nakano, Ayako Ikeda, Minoru Ueda, Masao Takeyama

Index: 10.1016/j.intermet.2018.01.009

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Abstract

The influence of a unique layered microstructure consisting of duplex-like region and equiaxed γ grain layers (γ bands) on the fatigue properties of Ti-48Al-2Cr-2Nb alloy bars fabricated by electron beam melting (EBM) was investigated at room temperature (RT) and 1023 K focusing on the angle (θ) between the building direction and cylinder (loading) axis. We found for the first time the fatigue strengths of the alloy bars with the layered microstructure depend strongly on the angle θ. Particularly, the fatigue strength of the alloy bars fabricated at θ = 45° is comparable to that of the hot isostatic pressing (HIP) treated cast alloys, even without HIP treatment. We also found the alloy bars fabricated at θ = 0° and 45° exhibit high fatigue strengths in the low-cycle fatigue life region at 1023 K similar to θ = 45° alloy bars at RT. These high fatigue strengths are caused by inhibition of the brittle main crack initiation by stress relaxation due to shear deformation at the γ bands and large plasticity of the alloys. These findings indicate that the alloys fabricated by EBM at θ = 45° with the unique layered microstructure have a great potential for aerospace and automobile applications.