Determination of the structure of α-β interfaces in metastable β-Ti alloys
Determination of the structure of α-β interfaces in metastable β-Ti alloys
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DOI：
10.1016/j.actamat.2018.03.003
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发表时间：
2018-05
期刊：
影响因子：
9.4
通讯作者：
Yufeng Zheng;Robert E. A. Williams;G. Viswanathan;W. Clark;H. Fraser
中科院分区：
文献类型：
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作者：
Yufeng Zheng;Robert E. A. Williams;G. Viswanathan;W. Clark;H. Fraser
研究了固溶淬火亚稳α钛合金Ti-5Al-5Mo-5V-3CR(wt%，Ti-5553)经600°C加热后，分别时效0和30min后，六方密排β析出物与体心立方β相界面形成的晶体和结构。这两个相均采用经典的Burgers取向，并用拓扑模型分析了观察到的界面结构，即它们包含了断续，以及作为晶格不变变形(LID)的β晶格位错。在高角环形暗场扫描电子显微镜下，沿两个相互垂直的方向观察了α/β界面的结构。沿[0001]α：[110]β方向观察，观察到一系列断开以适应α和β晶体之间的失配。虽然这些断口的间距不同，但与它们相关的台阶高度始终是{112}β面间间距的两倍，它们的Burgers矢b是[−0.019 0.019 0.034]β。当界面沿[1‘1’20]α：[1‘11]β方向观察时，在600°C时效0min的样品中，沿[0001]α：[110]β的两个晶格之间的失配非常小，以至于在视场内没有观察到失配或晶格不变的位错，这与其他更传统的钛合金中报道的界面结构相反。然而，老化30min后，界面结构平衡，并在容纳盖子的平台平面上观察到晶格位错，b=1 2[1‘1]β。α析出物的生长主要是通过从现有α析出物的尖端向β基质发射断开连接，并由此转化为α而发生的。这些结果结合拓扑模型的分析表明，该合金中hcpα相在体心立方β基体中的形核和长大可以用断裂运动来描述，同时伴随着适应α和β相组成差异所需的位移扩散。
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, ie 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.