Microstructure of cast γ-TiAl based alloy solidified from β phase region
来源期刊：中国有色金属学报(英文版)2011年第2期
论文作者：王岩 刘咏 杨广宇 李慧中 唐蓓
文章页码：215 - 222
关键词：γ-TiAl基合金; 显微组织; 相转变; β相; 凝固; 热处理
Key words：γ-TiAl based alloy; microstructure; phase transformation; β phase; solidification; heat treatment
摘 要：采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)及差示扫描量热仪(DSC)研究Ti-43Al-4Nb铸态合金及其热处理态合金的显微组织以及相转变行为。结果表明：通过从β相区凝固的方法可以获得组织细小的铸态Ti-43Al-4Nb合金；凝固过程中γ晶能够直接从β相中形核，β相与γ相沿初始α晶界共存，有效地抑制了铸态Ti-43Al-4Nb合金晶粒的长大；Ti-43Al-4Nb合金在凝固过程中的相转变顺序为L→L+β→β→α+β→α+βr→α+γ+βr→(α2+γ)片层+γ+βr；经1 250 °C、16 h热处理后，Ti-43Al-4Nb合金的显微组织与铸态组织相比有一定程度的粗化；由于Nb元素的充分扩散以及β相的非平衡状态，经过上述热处理过程后残余β相能够被完全消除。
Abstract: The microstructures and phase transformation of Ti-43Al-4Nb alloy in as-cast and heat-treated states were investigated by using optical microscopy, scanning and transmission electron microscopy as well as differential scanning calorimetry. The results show that a fine microstructure of the as-cast alloy can be obtained by solidifying through the β phase. γ grains can nucleate directly from the β phase. The coexistence of β phase and γ phase along primary α grain boundaries contributes to the decrease in the grain size of the as-cast alloy. The phase transformation sequence during solidification of the Ti-43Al-4Nb alloy is suggested as L→L+β→β→α+β→α+βr→α+γ+βr→lamellae(α2+γ)+γ+βr. The microstructure of the alloy after heat treatment at 1 250 °C for 16 h exhibits a certain coarsening compared with that of the as-cast state. The remnant β phase can be removed by the heat treatment process due to the diffusion of Nb and the non-equilibrium state of β phase.
