Three-dimensional study of grain scale tensile twinning activity in magnesium: A combination of microstructure characterization and mechanical modeling
Three-dimensional study of grain scale tensile twinning activity in magnesium: A combination of microstructure characterization and mechanical modeling
复制标题
镁晶粒拉伸孪生活动的三维研究：微观结构表征和机械建模的结合
DOI：
10.1016/j.actamat.2023.119043
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发表时间：
2023
期刊：
影响因子：
9.4
通讯作者：
Zeng X
中科院分区：
文献类型：
--
作者：
Zeng X
拉伸孪晶是六边形密排结构金属的主要变形模式，因此全面了解孪晶机制是非常重要的，这些机制目前还没有通过二维或小体积三维表征技术完全揭示。采用大面积三维电子背散射衍射（EBSD）测量和晶体塑性建模研究了镁合金的拉伸孪晶行为。结果表明，使用传统的二维EBSD扫描，拉伸孪晶活动被低估了。当压缩到屈服点时，2D的双频率比3D的低。研究了施密德因子（SF）对双胞胎的影响。几乎所有高施密德因子（SF>0.35）晶粒均为双晶。在中SF （0.35>=SF>=0.15）晶粒中观察到令人惊讶的82%的高孪晶频率，这是出乎意料的，因为中SF晶粒被认为是不利于孪晶的。在低SF （SF<0.15）晶粒中，由于孪晶体积小，从2D到3D EBSD孪晶频率略有增加。剪切应力在高SF晶粒中保持较高水平且均匀分布，有利于孪晶形核和长大。剪切应力在中间SF晶粒内分布不均，孪晶在正剪切应力区域内形核。低SF晶粒的剪切应力不利于孪晶，孪晶发生在应力积累的附近。同一晶粒的孪晶活动在不同层间存在差异。这主要是由于籽粒环境变化引起的应力波动所致。
Tensile twinning is a main deformation mode in hexagonal close packed structure metals, so it is important to comprehensively understand twinning mechanisms which are not fully disclosed using 2D or small volume 3D characterization techniques. A large area 3D electron backscatter diffraction (EBSD) measurement and crystal plasticity modeling were carried out to investigate the tensile twinning behaviors in a magnesium (Mg) alloy. The results showed that tensile twinning activity was underestimated using conventional 2D EBSD scans. When compressed to yield point, the examined twin frequency with 2D was lower than that using 3D EBSD. The effects of Schmid factor (SF) on twinning were investigated. Almost all high Schmid factor (SF>0.35) grains were twinned. A surprising high twin frequency of 82% in middle SF (0.35>=SF>=0.15) grains was observed, which was unexpected since the middle SF grains were believed to be unfavorable for twinning. The twin frequency in low SF (SF<0.15) grains was slightly increased from 2D to 3D EBSD due to the small volume of twins. The shear stress maintained a high level and was homogeneously distributed in high SF grains, facilitating twin nucleation and growth. The shear stress was distributed heterogeneously within the middle SF grains, and twins were nucleated within areas with positive shear stress. The shear stress in low SF grains was not favorable for twinning and twins occurred in the vicinity of stress accumulation. Twinning activities in the same grain varied on different layers. It was attributed to the stress fluctuation derived from grain environment changes.