일방향응고된 2상 TiAl 합금의 층상경계 방향제어

Abstract

The effect of Al concentration and third element addition on the directionally solidified (DS) TiAl alloys were systematically investigated in order to get a basic conception for control of lamellar boundary orientation. DS ingots have been grown by the arc melted unidirectional solidification equipment without seed materials. Some β stabilizing elements such as Mo, Nb and Cr have been added in order to increase phase field in the binary system. In the case of Ti-46Al-2Mo, Ti-96Al-2Mb and Ti-46Al-2Cr DS ingot grown at a growth rate of 90㎜ hr, it has been found that the lamellar orientation was aligned nearly 0˚ to 45˚ to the growth direction. Therefore, it could be suggested that there has been great possibility to align lamellar orientation by adding β stabilizing elements such as Mo, Nb and Cr. In the case of Ti-47.5Al-2.5Mo DS ingot grown at a growth rate of 180㎜/hr and 360㎜/hr, the lamellar boundary was nearly perpendicular to the growth direction. However, when the directional solidification was performed at a growth rate of 90㎜/hr, the lamellar boundary orientation of Ti-47.5Al-2.5Mo DS ingot was nearly parallel to the growth direction. These results indicate that lamellar boundary orientation of DS ingot may been affected by the growth rate as well as composition.