Microstructure evolution and phase transformation of the mushy zone in a quenched β-solidifying TiAl alloy

This study investigates the phase constitutions and transformations that occur in the mushy zone and in the adjacent phase fields of a directionally solidified Ti-44Al-8Nb-1Cr alloy via quenching technique. The results indicate that the mushy zone consists of unmelted & beta; dendrites and interdendritic liquid, whose formation can be attributed to the difference in melting point aroused by local heterogeneity in solutecontent. The & beta; dendrite is composed of numerous subgrains with various orientations. During quenching, the & beta; dendrite transforms into Widmanstatten & alpha; via a precipitation reaction, owing to the decreasing cooling rate caused by heat transfer from the surrounding liquid. Additionally, after quenching, the interdendritic liquid is transformed into & gamma; plates. Within the single & beta; phase field and the lower part of the mushy zone, a massive transformation of & beta; to & gamma; occurs . Conversely, in the & beta;-F & alpha; phase field, both & beta; and & alpha; phases are retained to ambient temperature. During the heating process, the transformation of & alpha; - & beta; gives rise to the formation of & beta; variants, which affects the orientation of & beta; dendrites in the mushy zone. The growth kinematics of the & alpha; - & beta; transformation was elucidated, revealing the preferential growth directions of ( 111 ) and ( 112 ) for & beta; variants. Furthermore, this study presents an illustration of the formation process of the mushy zone and the microstructural evolution during the heating and quenching process. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.