Effect of growth rate and diameter on microstructure and hardness of directionally solidified Ti-46Al-8Nb alloy  

生长速度与试样直径对定向凝固Ti-46Al-8Nb合金显微组织和硬度的影响(英文)

作　　者：刘国怀[1] 李新中[2] 张元[2] 陈瑞润[2] 苏彦庆[2] 郭景杰[2] 傅恒志[2] 王昭东[1] 王国栋[1] 

机构地区：[1]东北大学轧制技术与连轧自动化国家重点实验室,沈阳110819 [2]哈尔滨工业大学材料科学与工程学院,哈尔滨150001

出　　处：《Transactions of Nonferrous Metals Society of China》2014年第12期4044-4052,共9页中国有色金属学报（英文版）

基　　金：Projects(51071062,51274077,51271068)supported by the National Natural Science Foundation of China;Project(2011-P03)supported by Open Fund of State Key Laboratory of Mold and Die Technology of Huazhong University of Science and Technology;Project(HIT.NSRIF.2013002)supported by the Fundamental Research Funds for the Central Universities,China;Project(2011CB605504)supported by the National Basic Research Program of China

摘　　要：Bridgman-type directional solidification experiments were conducted for Ti-46Al-8Nb （mole fraction, %） alloy. The effects of the growth rate and the diameter on the microstructure, phase transition and hardness of the alloy were investigated. The results show that with the increase of the growth rate and the decrease of the diameter, the fullyβphase solidification changes to the peritectic solidification, and the final microstructure is composed of theα2/γlamellar structure and a multiphase microstructure （B2 phase,α2/γlamellar structure） respectively, which can be attributed to the solute enrichment resulting from the decreasing diffusion and convection ability. The occurrence of peritectic reaction at high growth rate promotes the solute segregation heavily and the coarse lamellar spacing in Al-and Nb-rich region, which greatly decreases the hardness values and leads to the discontinuity of the hardness curves with the increase of the growth rate. Comparatively, the Ti-46Al-8Nb alloy has lower hardness values than the other applied TiAl-based alloys in previous studies.对Ti-46Al-8Nb(摩尔分数,%)合金进行布里奇曼型定向凝固实验,考察生长速度和试样直径对合金显微组织、相变路径和硬度的影响。结果表明,随着生长速度的增加和试样直径的减小,凝固过程由完全β相凝固转变为具有包晶反应的凝固过程,其最终显微组织为α2/γ层片及有α2/γ层片和B2相组成的多相组织。以上结果是由扩散和对流的减弱造成的溶质富集而引起的。包晶反应的发生往往导致严重的溶质偏析,其中溶质Al和Nb的偏析使得层片组织较为粗大。因此,在较高生长速度下发生包晶反应时,合金硬度值急剧下降,硬度曲线随着生长速度的增加呈不连续变化。严重溶质偏析导致的粗大层片组织也使得该成分合金的硬度低于其他Ti Al基合金的硬度。

关 键 词：TiAl alloy directional solidification growth rate DIAMETER phase transition 

分 类 号：TG146.23[一般工业技术—材料科学与工程]