Effect of cooling rates on microstructures evolution and nanohardness of rapidly solidified Ti-48Al-4Cr alloy

The effect of cooling rates on microstructure of Ti-48Al-4Cr (at%) alloy rapidly solidified at different wheel speeds were experimentally investigated by the single roller melt-spinning technique. The results indicate that after rapid solidification at the wheel speed of 10 and 20 m/s, the microstructures mainly consist of equiaxed γ phase, a few volume fraction of α₂, B2 phase particles and lamellar structures in the γ phase matrix. At the wheel speed of 30 m/s, the matrix changes to α₂ phase and the lamellar structures disappear. The nanohardness increases with the cooling rate increasing. It enhances from 4.98±0.10 GPa under normal pressure to 7.48±0.16 GPa under 4 GPa. The nanohardness increases from 5.04±0.09 GPa of conventional cast Ti-48Al alloy to 10.48±0.13 GPa of rapidly solidified Ti-48Al-4Cr alloy with the wheel speed of 30 m/s. This research has provided the basis of further study on the microstructures, reducing the segregation and enhancing the mechanical properties of TiAl alloy.