Microstructure evolution and microhardness of TiAl based alloy blade by vacuum suction casting

The TiAl based alloy blade has been obtained by vacuum suction casting with metal mold. The numerical simulation and experiment were carried out to study the Niyama criterion for shrinkage defects. Comparing the numerical and experimental results, the Niyama criterion in the metal mold vacuum suction casting is defined, which is 0.15. Furthermore, the microstructures of Ti47Al alloy under sub-rapid solidification are analyzed by EBSD and BSE. The results show that with the increase of thickness, the width of columnar grains at the edge and the size of equiaxed grains at the center of the castings increase. Under sub-rapid solidification conditions, the solidification structure of Ti47Al binary alloy consists of alpha(2), gamma and B2 phase, but their relative content deviate from equilibrium solidification. With the decrease of the thickness, the content of gamma phase rises, and the content of alpha(2) reduce. When the thickness exceeds 2 mm, the content of B2 phase is almost unchanged, and the content of B2 phase with 1 mm thickness is almost twice that of other thickness, and the B2 phase is mainly distributed between the lamellae. Sub-rapid solidification conditions can not break the degree relationship between alpha(2)and gamma phase, that is, (0001)alpha(2)parallel to(111)gamma.