摘要
选择GE公司开发的Ti-46Al-2Cr-2Nb工程合金,采用Bridgman定向凝固技术,通过改变晶体生长距离(5—30 mm)的方法,研究了晶体在渐进生长过程中领先相及其生长取向的演变规律.结果发现,在固定的温度梯度(G=18 K/mm)与生长速度(v=20μm/s)下,定向凝固初始阶段合金的领先相为β相.但随着凝固距离的增加,溶质组元A1在枝晶间的液相中富集程度逐渐增大,导致出现L+β→α包晶反应.随着凝固距离的进一步增加,α和β相的竞争生长加剧,最终导致领先相由β相转变为α相.通过EBSD分析表征了与凝固进程相关的领先相生长取向,在定向凝固初始阶段,领先相β的晶体沿其择优方向〈100〉β生长;在包晶反应过程中,凝固析出的β相和α相遵循{110}β//{0001}α取向关系,由此导致当领先相转变为α相后,晶体的生长方向偏离其择优方向〈0001〉α.
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/3 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＋/3 --＊ a. With further increase of the growth length, growth competition between primary/3 phase and peritectic a phase is promoted, leading to gradual transition of primary phases from/3 phase to a phase. The growth direction of primary phase in different stages of solidification has been characterized by EBSD analysis. The results indicate that primaryβ 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 a2 grains formed from primaryβ phase and peritectic a phase,it is found that peritectic a phase related to primary β phase by the {110}z /{0001}α orientation relationship. Therefore, as the primary phase has transformed to α phase, the growth direction deviates from its preferential growth direction 〈0001〉 at an angle of 45.9°. The growth direction of a phase formed after the primary phase transformation is determined not only by the kinetic factors of solidification, but also by the phase exiting at the beginning of directional solidification. These results provide fundamental references for understanding and controlling the lamellar orientation of GE alloys.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2013年第9期1061-1068,共8页
Acta Metallurgica Sinica
基金
国家自然科学基金项目51071062
51274077和51271068
国家重点基础研究发展计划2011CB605504
中央高校基本科研业务费专项资金项目HIT.NSRIF.2013002资助~~
关键词
TIAL合金
定向凝固
初生相
凝固历程
TiAl alloy, directional solidification, primary phase, solidification process
