Abstract The crystallography and structure of the interfaces formed between refined hexagonal close packed (hcp) α precipitates and the body centered cubic (bcc) β matrix in a solution-treated and quenched metastable β titanium alloy, Ti-5Al-5Mo-5V-3Cr (wt%, Ti-5553), were investigated after heating to 600 °C and subsequently aging for 0 and 30 min, respectively. The two phases adopted the classical Burgers orientation, and the observed interfacial structures were analyzed using a topological model, i.e. they contained disconnections, as well as β crystal lattice dislocations acting as a lattice invariant deformation (LID). The structure of the α/β interface was observed along two mutually perpendicular directions, in high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Viewed along the [ 0001 ] α : [ 110 ] β directions, an array of disconnections was observed to accommodate the misfit between the α and β crystals. While the spacing of these disconnections varied, the step height associated with them was always twice the { 112 } β interplanar spacing, and their Burgers vector b was [ − 0.019 0.019 0.034 ] β . When the interface was viewed along the [ 1 ¯ 1 ¯ 20 ] α : [ 1 ¯ 11 ] β direction, in the sample aged for 0 min at 600 °C the misfit between the two lattices along [ 0001 ] α : [ 110 ] β was so small that no misfit or lattice invariant dislocations were observed within the field of view, in contrast with the interface structure reported in other more conventional titanium alloys. After aging the sample for 30 min, however, the interfacial structure equilibrated, and crystal lattice dislocations were observed on the terrace planes, accommodating the LID, with b = 1 2 [ 1 ¯ 1 ¯ 1 ¯ ] β . Growth of the α precipitates is shown to occur principally by the emission of disconnections from the tip of the existing α precipitates into the β matrix, and its resulting conversion to α. These results, combined with analysis using the topological model, show that the nucleation and growth of the hcp α phase from the bcc β matrix in this alloy can be described in terms of the motion of disconnections, accompanied by the displacive diffusion necessary to accommodate the differences in composition between the α and β phases.

中文翻译：

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亚稳态β-Ti合金中α-β界面结构的测定

摘要 在固溶处理和淬火亚稳态 β 钛合金 Ti-5Al-5Mo-5V-3Cr 中，精制六方密堆积 (hcp) α 沉淀物与体心立方 (bcc) β 基体之间形成的界面的晶体学和结构(wt%, Ti-5553)，分别在加热到 600 °C 和随后老化 0 分钟和 30 分钟后进行研究。两相采用经典的 Burgers 取向，并使用拓扑模型分析观察到的界面结构，即它们包含断开连接，以及充当晶格不变变形 (LID) 的 β 晶格位错。在高角度环形暗场扫描透射电子显微镜 (HAADF-STEM) 中，沿两个相互垂直的方向观察了 α/β 界面的结构。沿 [0001] α 观察：[ 110 ] β 方向，观察到一系列断开以适应 α 和 β 晶体之间的错配。虽然这些断开的间距不同，但与它们相关的台阶高度始终是 { 112 } β 面间距的两倍，并且它们的 Burgers 矢量 b 是 [ − 0.019 0.019 0.034 ] β 。当沿[ 1¯ 1 ¯ 20 ] α : [ 1 ¯ 11 ] β 方向观察界面时，在600 °C 时效0 min 的样品中，沿[ 0001 ] α : [ 110 ] 两个晶格之间的错配β 非常小，以至于在视场内没有观察到错配或晶格不变位错，与其他更传统的钛合金中报道的界面结构形成对比。然而，在样品老化 30 分钟后，界面结构平衡，并且在平台平面上观察到晶格位错，容纳 LID，其中 b = 1 2 [ 1¯ 1 ¯ 1 ¯ ] β 。显示 α 沉淀物的生长主要是通过从现有 α 沉淀物的尖端发射到 β 基质中的断开，以及由此产生的转化为 α 来发生的。这些结果与使用拓扑模型的分析相结合，表明该合金中 hcp α 相从 bcc β 基体的成核和生长可以用断开的运动来描述，伴随着适应α 相和 β 相之间的成分差异。