Variant selection within one β grain in laser solid formed Ti-6Al-4V alloys
Variant selection within one β grain in laser solid formed Ti-6Al-4V alloys
复制标题
激光实体成形 Ti-6Al-4V 合金中一个 β 晶粒内的变体选择
DOI：
10.1016/j.matchar.2022.111744
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发表时间：
2022
影响因子：
4.7
通讯作者：
Jincheng Wang
中科院分区：
文献类型：
--
作者：
Jiankai Ma;Yashan Zhang;Junjie Li;Zhijun Wang;Jincheng Wang
钛合金中的变体选择是一种常见但复杂的现象，不仅受影响变体形核过程的微观组织特征（如晶粒取向、晶界和残余α相）的控制，而且还受一些动力学因素（如冷却速率和残余应力）的显著影响，特别是对于增材制造的钛合金。为确定冷却速率对激光固态成形Ti-6Al-4V合金变体选择的影响，系统研究了不同冷却速率下激光固态成形Ti-6Al-4V合金同一β晶粒不同区域中α变体的选择。电子背散射衍射（EBSD）数据表明，虽然12种α变体均在不同冷却速率下出现，但在不同冷却速率下，某些变体的面积百分比明显偏离相应的理论值。为了定量表征变异选择的变化，进一步统计分析了以角/轴类型区分的α/α边界的长度分数。结果表明，Ⅳ型α/α边界的长度分数（63.26°/[−10 5 5 -3]）在冷却速率较高时大于其他类型（底部区域）由于高残余应力，而在低冷却速率下（中间区），Ⅱ型（60°/[11-20]）的α/α边界占主导地位，这可能归因于β → α相变过程中的自适应机制。获得的关于冷却速率对α变体选择的影响的见解有助于理解LSF锻造钛合金的微观组织演变。
Variant selection, a common but complex phenomenon in Ti alloys, is not only governed by microstructural characteristics that affect the nucleation process of variants, such as grain orientation, grain boundaries, and residual α phase, but also remarkably influenced by some kinetic factors, such as cooling rate and residual stress, especially for the additive manufactured Ti alloys. To determine the influence of cooling rates on variant selection of laser solid formed (LSF) Ti-6Al-4V alloys, the selection of α variant in different zones of LSFed samples (possessing different cooling rates) but belonging to one single β grain was systematically studied. With the electron backscatter diffraction (EBSD) data, it was revealed that, though all 12 kinds of α variants appeared under different cooling rates, the area percentage of some variants remarkably deviated from the corresponding theoretical values at different cooling rates. To characterize the change of variant selection quantitatively, the length fraction of α/α boundary distinguished by types of angle/axis was further analyzed statistically. The results show that the length fraction of α/α boundary of type IV (63.26°/[−10 5 5 –3]) is larger than that of other types when the cooling rate is high (bottom zone) due to the high residual stress, while at low cooling rates (middle zone), the α/α boundary of type II (60°/[11–20]) dominates, which could be attributed to the self-accommodation mechanism during the β → α phase transition. The insights gained about the influence of cooling rate on the selection of α variant are helpful for understanding the microstructural evolution in LSFed Ti alloys.