Ti_3Al+TiAl片层组织的不连续粗化转变

DISCONTINUOUS COARSENING OF Ti3Al+TiAl LAMELLAE

为细化铸造ＴｉＡｌ基合金的显微组织，将成分为Ｔｉ４４．９Ａｌ和Ｔｉ４４．３Ａｌ３．０Ｃｒ（摩尔分数，％）的两种合金在略高于ＴｉＡｌ共析温度的１１５０℃进行长时保温处理。结果表明，保温一定时间后，两种合金中的Ｔｉ３Ａｌ＋ＴｉＡｌ片层组织都会发生不连续粗化转变，这种转变的结果能在一定程度上细化合金的晶粒尺寸，其中Ｔｉ４４．３Ａｌ３．０Ｃｒ合金的晶粒细化效果更佳。进一步的研究表明，二元Ｔｉ４４．９Ａｌ合金中的片层组织的不连续粗化转变近似符合最大熵增率原理和Ｌｉｖｉｎｇｓｔｏｎ的稳态扩散模型，其转变控制因素为晶界扩散控制；合金元素Ｃｒ的加入，原始片间距的细化及表面预变形都会大大促进这种不连续粗化转变过程。

In order to obtain fine grain microstructures in ascast TiAl base alloys, alloys of Ti44.9Al, Ti44.3Al3.0Cr(mole fraction, %)were heat treated at 1 150 ℃ for long times. The results show that the Ti3Al+TiAl lamellae in alloys discontinuously coarsen gradually after heat treatment, and this kind of discontinuous coarsening transformation can refine grain size of alloys, the better result of refining grains was achieved in Ti44.3Al3.0Cr alloy.Further study shows that the maximum ratio of entropy production principle and Livingston's steadystate diffusion model can appoximately be used to explain the discontinuous coarsening happening in Ti44.9Al alloy, the controlling mechanism in this alloy is grain boundary diffusion, the adding of Cr, the decrease of lamellar spacing and prestrain in surface will accelerate discontinuous coarsening greatly.