Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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Transactions of Nonferrous Metals Society of China

Vol. 21    No. 2    February 2011

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Microstructure of cast γ-TiAl based alloy solidified from β phase region
WANG Yan1, LIU Yong1, YANG Guang-yu1, LI Hui-zhong2, TANG Bei2

1. State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083, China;
2. School of Materials Science and Engineering, Central South University, Changsha 410083, China

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.


Key words: γ-TiAl based alloy; microstructure; phase transformation; β phase; solidification; heat treatment

ISSN 1004-0609
CN 43-1238/TG

ISSN 1003-6326
CN 43-1239/TG

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