Sudden stress-induced transformation events during nanoindentation of NiTi shape memory alloys
Sudden stress-induced transformation events during nanoindentation of NiTi shape memory alloys
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DOI：
10.1016/j.actamat.2014.05.061
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发表时间：
2014-10
期刊：
影响因子：
9.4
通讯作者：
G. Laplanche;J. Pfetzing‐Micklich;G. Eggeler
中科院分区：
文献类型：
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作者：
G. Laplanche;J. Pfetzing‐Micklich;G. Eggeler
本研究探讨奥氏体镍钛形状记忆合金在纳米压痕过程中应力诱发马氏体的形成，其中应力诱发马氏体在室温下是稳定的。选择具有[1 1 1]表面法线的单个颗粒在扫描电子显微镜中用于球形非原位和原位纳米压痕。原位载荷-位移曲线表明，在压头尖端和样品之间的接触区周围形成痕迹的同时发生了几个弹出。这些迹线围绕着残留的尘埃呈现出三重对称性。压痕诱导的表面浮雕形状恢复之前和之后的原子力显微镜的详细研究允许识别六个孪晶马氏体板的形成。死后的显微组织特征表明，这些孪晶马氏体板生长的施加的负载是增加。实验观察到的孪晶马氏体板的激活是合理的解析计算的剪切应力和机械相互作用的能量密度。最后，在原位纳米压痕的结果结合死后的微观结构表征表明，最有可能的变形机制负责弹出事件对应于突然增加的孪晶马氏体板的厚度。
This study investigates the stress-induced formation of martensite during nanoindentation of an austenitic NiTi shape memory alloy, where stress-induced martensite is stable at room temperature. An individual grain with a [1 1 1] surface normal was selected for spherical ex situ and in situ nanoindentation in a scanning electron microscope. The in situ load–displacement curves show several pop-ins which occur concomitantly with the formation of traces around the contact zone between the indenter tip and the sample. These traces exhibit a threefold symmetry around the remnant indent. A detailed study of the indentation-induced surface relief by atomic force microscopy before and after shape recovery allows to identify the formation of six twinned martensite plates. Post-mortem microstructural characterization shows that these twinned martensite plates are growing as the applied load is increasing. The activation of the experimentally observed twinned martensite plates is rationalized by analytical calculations of resolved shear stress and mechanical interaction energy density. Finally, the in situ nanoindentation results in combination with the post-mortem microstructural characterization show that the most likely deformation mechanism responsible for pop-in events corresponds to sudden increases of the thicknesses of twinned martensite plates.