Abstract In this study, the precipitation mechanism of secondary α-phase and formation of a bimodal microstructure in Ti6242S alloy cooled from the α + β phase field were investigated. It was found that grain boundary α (αGB) precipitated preferentially not only at the triple junction of the β/β boundary, but also at the equiaxed αp/β interface and then grew along the β/β boundary. The nucleation and growth of the intragranular α (αI) phase were influenced by β grain boundary (GB), the pre-existing equiaxed α (αp), and adjacent αI grain. αI grain preferentially precipitated at equiaxed αp/β interface regardless of the presence or absence of a Burgers orientation relationship (BOR) between αp and β phases; when there was no BOR, αI preferentially precipitated due to self-accommodation (i.e. a special orientation relationship) between the αp and adjacent αI grains, to minimize the total transformation-strain energy. Meanwhile, two types of nucleation and growth modes (interface instability and sympathetic nucleation) coexisted in their precipitations. Moreover, several microtextured areas (large areas of α phase with similar crystallographic orientations) were observed in the obtained bimodal microstructure. This can be attributed to the fact that the special α variant always occupied a large area by preferential nucleation and growth, which further confirmed the role of the BOR and self-accommodation.

中文翻译：

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α+β相场冷却Ti6242S合金二次α相析出机制及双峰组织形成

摘要 本研究研究了从α+β相场冷却的Ti6242S合金中二次α相的析出机制和双峰组织的形成。发现晶界α (αGB) 不仅在β/β 边界的三重结处优先析出，而且在等轴αp/β 界面处也优先析出，然后沿β/β 边界生长。晶内α (αI) 相的形核和生长受β 晶界(GB)、预先存在的等轴α (αp) 和相邻的αI 晶粒的影响。无论αp和β相之间是否存在伯格斯取向关系（BOR），αI晶粒优先在等轴αp/β界面析出；当没有 BOR 时，αI 由于自调节而优先沉淀（即 αp 和相邻的 αI 晶粒之间的特殊取向关系），以最小化总转变应变能。同时，两种类型的成核和生长模式（界面不稳定和交感成核）在它们的沉淀中并存。此外，在获得的双峰显微组织中观察到几个显微纹理区域（具有相似晶体取向的大面积 α 相）。这可以归因于特殊的α变体总是通过优先成核和生长占据大面积，这进一步证实了BOR和自调节的作用。在获得的双峰显微组织中观察到几个显微纹理区域（具有相似晶体取向的大面积 α 相）。这可以归因于特殊的α变体总是通过优先成核和生长占据大面积，这进一步证实了BOR和自调节的作用。在获得的双峰显微组织中观察到几个显微纹理区域（具有相似晶体取向的大面积 α 相）。这可以归因于特殊的α变体总是通过优先成核和生长占据大面积，这进一步证实了BOR和自调节的作用。