Although massive transformation has been increasingly observed in titanium alloys, the decomposition mechanism of the massive transformation product (α) is still unclear. Here, the β→α→α+β continuous phase transformation in Ti-6Al-4V alloy during cooling was studied. We found that massive transformation occurs at a moderate cooling rate below 291.5 °C/s, forming irregular featureless α. The thermodynamically unstable α is supersaturated with β stabilizers, and it tends to decompose into ultrafine α+β structure during the continuous cooling at ever-lower cooling rates and temperatures. In the initial stage of α decomposition, misfit dislocations appear as a predecessor and split α into strips. Accompanied by the elemental redistribution, misfit dislocations are accommodated and replaced by β phase. Both the formation and decomposition of α follow the typical Burgers orientation relationship.

中文翻译：

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Ti-6Al-4V合金β→αm→α+β连续相变过程中超细α+β结构的形成机制

尽管在钛合金中越来越多地观察到块状相变，但块状相变产物（α）的分解机制仍不清楚。本文研究了Ti-6Al-4V合金冷却过程中β→α→α+β连续相变。我们发现，在低于 291.5 °C/s 的中等冷却速率下会发生大量转变，形成不规则、无特征的 α。热力学不稳定的α与β稳定剂过饱和，并且在不断降低的冷却速率和温度下连续冷却过程中倾向于分解成超细α+β结构。在α分解的初始阶段，失配位错作为前身出现，并将α分裂成条带。伴随着元素的重新分布，失配位错被β相容纳并取代。 α的形成和分解都遵循典型的伯格斯取向关系。