Where and when are dislocations induced by thermal cycling in Ti-Ni shape memory alloys?
Where and when are dislocations induced by thermal cycling in Ti-Ni shape memory alloys?
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DOI：
10.1016/j.actamat.2022.118588
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发表时间：
2022-12-09
期刊：
影响因子：
9.4
通讯作者：
Nishida, M.
中科院分区：
文献类型：
--
作者：
Akamine, H.;Heima, A.;Nishida, M.
系统地研究了Ti-Ni形状记忆合金在热循环过程中位错产生的位置和时间。随着Ni含量的增加，热循环时相变温度的降低变得不那么明显，这与扫描电子显微镜观察到的位错密度相一致。第一次热循环后相变诱导位错的排列重现了B19‘马氏体的自适应结构。三维可视化显示，位错在第一次热循环后呈现复杂的螺旋状，是由于沿深度方向平行于(111)B2的相对简单的细长位错环沿{110}B2重复投影所致。在初始转变的马氏体中没有观察到位错沿孪晶界的存在，而在第二次热循环形成的马氏体中有大量的位错平行于{110}B_2面的轨迹。结果表明，相变诱发位错环是在反向相变过程中产生的，而不是在正向相变过程中产生的。还讨论了相变诱导位错的可能源位错。
Systematic experiments were performed to determine where and when dislocations are induced during the thermal cycling of Ti-Ni shape memory alloys. The decrease in transformation temperatures upon thermal cycling became less pronounced with increasing Ni concentration, which was supported by the dislocation densities estimated from scanning transmission electron microscopy observations. The arrangement of transformation-induced dislocations after the 1st thermal cycle reproduced the self-accommodation structure of B19' martensite. Three-dimensional visualization revealed that the complex spiral appearance of the dislocations after the 1st thermal cycle was attributable to the duplicated projection of relatively simple elongated dislocation loops aligned in the depth direction parallel to (111)B2 along {110}B2. No dislocations were observed along the twin boundary in the initially transformed martensite, whereas there were numerous dislocations parallel to the trace of the {110}B2 planes in the martensite formed upon the 2nd thermal cycle. The results suggest that the transformation-induced dislocation loops were generated during the reverse transformation rather than the forward transformation. The possible source site of the transformation-induced dislocations is also discussed.