Microstructure and Metastable Phase in Rapidly Solidified TiAl Alloy Prepared by Vacuum Suction Casting

Effect of the cooling rates on microstructure and metastable phase formation in Ti-50Al-2Cr-2Nb alloy is investigated by vacuum suction casting to realize rapid solidification by chilling Cu-mold. The temperature distribution field is simulated by the ANSYS software, and the cooling rates are calculated about 6.0 x 10(3)-2.2 x 10(4) K s(-1) and 5.3 x 10(4)-6.0 x 10(4) K s(-1), respectively. The results show that phase selection and microstructural evolution are closely related to cooling rates. The transformation of primarily formed alpha phase into beta phase from directional growth zone to the mushy zone determined by microstructural analysis at the cooling rate of 6.0 x 10(3) K s(-1), indicates the occurrence of phase selection and the formation of metastable phase. In addition, the occurrence of massive transformation in the surface chilling zone is generally different from that of heat treatment due to high cooling rates during suction casting.