Abstract In this study, TiAl alloy with nominal composition of Ti-43.5Al-6V-1Cr was fabricated by inductive skull melting technology. Microstructure evolution and microstructure formation mechanism were invested by quenching experiments. The results show that Ti-43.5Al-6V-1Cr alloy consists of lamellar colony (α2/γ), isolated γ phase and B2 phase. Phase transition equations and reaction temperatures during heating from RT to 1350℃ were identified: α2→γ, 835℃; α2→B2+γ, 990℃; α2+B2+γ→B2+γ, 1132℃; B2+γ→α+γ, 1144℃; γ→α, 1183℃; α+γ→α+β+γ, 1278℃; α+β+γ→α+β, 1290℃; α+β→β, 1313℃. It’s found that adding of β-stabilizing elements makes β phase field of Ti43.5Al6V1Cr alloy expand to Al rich side, decreases temperature of β→α transition by 127℃ and causes β+α+γ phase field appearing in the phase diagram. Orientation relation (111)B2//(110)γ was found between B2 and isolated γ phase, besides (110)B2//(111)γ(K-S relation), the match of the two phases declares that β phase is parent phase of isolated γ phase. Above all, the phase transformation process during heating and cooling was deduced. During heating it’s: α2/γ+B2+γ→B2+γ→α+γ→β+α+γ→α+β→β, while during cooling it’s L→L+β→β→α+β→α+β+γ →α+B2+γ→α2/γ+B2+γ. Besides, the microstructure evolution mechanism was explained and depicted in schematic.

中文翻译：

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β-凝固γ-TiAl合金的相变和微观结构演变

摘要 本研究采用感应壳壳熔炼技术制备标称成分为Ti-43.5Al-6V-1Cr的TiAl合金。通过淬火实验研究了组织演变和组织形成机制。结果表明，Ti-43.5Al-6V-1Cr合金由层状群落(α2/γ)、孤立的γ相和B2相组成。确定了从室温加热到1350℃的相变方程和反应温度：α2→γ，835℃；α2→B2+γ，990℃；α2+B2+γ→B2+γ，1132℃；B2+γ→α+γ，1144℃；γ→α，1183℃；α+γ→α+β+γ，1278℃；α+β+γ→α+β，1290℃；α+β→β，1313℃。发现β稳定元素的加入使Ti43.5Al6V1Cr合金的β相场向富Al侧扩展，β→α相变温度降低127℃，相图中出现β+α+γ相场。在B2和孤立的γ相之间发现了取向关系（111）B2//（110）γ，除（110）B2//（111）γ（KS关系）外，两相的匹配表明β相是母相孤立的 γ 相。首先，推导出加热和冷却过程中的相变过程。加热时为：α2/γ+B2+γ→B2+γ→α+γ→β+α+γ→α+β→β，冷却时为L→L+β→β→α+β→α+ β+γ →α+B2+γ→α2/γ+B2+γ。此外，还对微观结构演化机制进行了解释和示意图描述。