Microstructure and Fatigue Properties of TiAl with Unique Layered Microstructure Fabricated by Electron Beam Melting

In Ti-48Al-2Cr-2Nb (at.%) alloys fabricated by electron beam melting (EBM), a unique layered microstructure composed of duplex-like region and equiaxed gamma grains (gamma bands) is formed at an appropriate process condition. The fatigue behavior of the TiAl alloy fabricated by EBM at an angle (theta) of 90 degrees between the building direction and loading axis was investigated focusing on the layered microstructure and test temperature. At room temperature (RT), fatigue strength at theta = 90 degrees is higher than that at theta = 0 degrees. In particular, in low-cycle fatigue life region, the fatigue properties at theta = 90 degrees without hot isostatic pressing (HIP) are comparable to those of the cast alloys with HIP. The gamma bands act as an effective barrier to the crack propagation, resulting in high fatigue strength at RT. On the other hand, the fatigue strength at theta = 90 degrees is lower than that at theta = 0 degrees in low-cycle fatigue life region at 1023 K, since the gamma bands cannot suppress the crack propagation at 1023 K. However, at 1023 K, the fatigue strength at theta = 90 degrees in the low-cycle region is similar to that of the cast alloys with HIP, due to the fine grain size after EBM.