Observations on {332} twinning-induced softening in Ti-Nb Gum metal
Observations on {332} twinning-induced softening in Ti-Nb Gum metal
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DOI：
10.1016/j.msea.2018.03.062
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发表时间：
2018-05
期刊：
影响因子：
6.4
通讯作者：
Sumin Shin;Chaoyi Zhu;K. Vecchio
中科院分区：
文献类型：
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作者：
Sumin Shin;Chaoyi Zhu;K. Vecchio
对亚稳态的Ti-23Nb-0.7Ta-2Zr-1.0O(at%)合金进行了热机械循环处理，以控制孪晶诱发塑性效应的激活导致的机械孪晶的体积分数。电子背散射和X射线衍射分析表明，循环过程中产生的变形带仅为{332}<； 113 ；β孪晶。还观察到，随着循环次数的增加，孪晶的比例显著增加，导致了明显的软化效应。为了揭示微观组织演化和力学响应的相关微观尺度特征(如几何取向和应力集中)，根据实验观察结果估算了晶粒的局部施密德因子和几何必需的位错密度，并与变形孪生进行了关联。建立了孪晶织构演化引起的局部几何施密德因子与软化行为之间的良好相关性，以及局部应力集中对该种Ti-Nb胶金属微观组织演化的影响。高孪晶组织显著降低了β钛合金的显微硬度(约为未孪晶组织的18%)，并建立了一种可能的变形机制，以提高亚稳态合金的塑性，而弹性性能没有明显的变化。
Thermomechanical-cycling processes were applied to a metastable Ti-23Nb-0.7Ta-2Zr-1.0O (at%) alloy to control a volume fraction of mechanical twins, resulting from activation of twinning-induced plasticity effects. Analysis of the microstructure features designed using electron backscattering and X-ray diffraction revealed the deformation bands induced by the cycling process were characterized as only {332}< 113 >βtwinning. It was also observed that the fraction of twins was significantly increased with increasing the number of the cycles in the process, resulting in a pronounced softening effect. To shed a light on the relevant micro-scale features (e.g., geometric orientation and stress concentrations) responsible for the microstructure evolution and mechanical response, the local Schmid factor of grains and geometrically-necessary dislocation densities were evaluated from experimentally observed results, and correlated with deformation twinning. A good correlation between the local geometric Schmid factor and softening behavior, due to texture evolution within twins was established, as well as the effect of local stress concentrations on microstructure evolution of this Ti-Nb Gum metal. Significant decrease in micro-hardness (approximately 18% from untwinned structure) was achieved by highly twinned structure, and a possible deformation mechanism was established to enhance ductility without evident elastic properties variation in metastable β Ti alloys.