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| DEPENDENCE OF PRIMARY PHASE AND ITS GROWTH DIRECTION ON SOLIDIFICATION PROCESS IN DIRECTIONALLY SOLIDIFIED Ti－46Al－2Cr－2Nb ALLOY |
| ZHANG Yuan, LI Xinzhong, LIU Guohuai, SU Yanqing, GUO Jingjie, FU Hengzhi |
| School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 |
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Cite this article:
ZHANG Yuan, LI Xinzhong, LIU Guohuai, SU Yanqing, GUO Jingjie, FU Hengzhi. DEPENDENCE OF PRIMARY PHASE AND ITS GROWTH DIRECTION ON SOLIDIFICATION PROCESS IN DIRECTIONALLY SOLIDIFIED Ti－46Al－2Cr－2Nb ALLOY. Acta Metall Sin, 2013, 49(9): 1061-1068.
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Abstract GE alloy Ti－(46－-48)Al－2Cr－2Nb (atomic fraction) is well known for its high strength and improved ductility. The primary phase and its growth direction are important in controlling the lamellar direction of GE alloys. However it is greatly affected by solidification conditions. In this work, primary phase and its growth direction have been investigated by carrying out Bridgman－type directional solidification with different growth lengths ranging from 5 to 30 mm on Ti－46Al－2Cr－2Nb alloy. It is found that the primary phase is β at the beginning of directional solidification with constant temperature gradient (G=18 K/mm) and growth rate (v=20 μm/s). With the increase of growth length, Al gradually concentrates in the liquid between primary dendrites, which leads to the peritectic reaction L+β→α. With further increase of the growth length, growth competition between primary β phase and peritectic α phase is promoted, leading to gradual transition of primary phases from β phase to α phase. The growth direction of primary phase in different stages of solidification has been characterized by EBSD analysis. The results indicate that primary β phase has a growth direction parallel to its preferential growth direction <100>β at the initial stage of solidification. By comparing the growth directions of the α2 grains formed from primary β phase and peritectic α phase,it is found that peritectic α phase related to primary β phase by the {110}β //{0001}α orientation relationship. Therefore, as the primary phase has transformed to α phase, the growth direction deviates from its preferential growth direction <0001>α at an angle of 45.9°. The growth direction of α phase formed after the primary phase transformation is determined not only by the kinetic factors of solidification, but also by the β phase exiting at the beginning of directional solidification. These results provide fundamental references for understanding and controlling the lamellar orientation of GE alloys.
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Received: 21 May 2013
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