TEM investigation of the microstructural evolution during nanoindentation of NiTi
TEM investigation of the microstructural evolution during nanoindentation of NiTi
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NiTi 纳米压痕过程中微观结构演变的 TEM 研究
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
G. Eggeler
中科院分区：
文献类型：
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作者：
J. Pfetzing;M. Wagner;T. Simon;A. Schaefer;C. Somsen;G. Eggeler
在形状记忆合金的纳米压痕过程中连续测量载荷和位移可以对纳米尺度的伪弹性进行详细研究。然而，所得的载荷-位移数据同时反映了几种弹性和非弹性变形过程（即应力诱导的马氏体转变、塑性变形）。在本研究中，我们进行微观结构研究，以分析富镍合金中这些机制之间的复杂相互作用。通过透射电子显微镜对不同最大压痕载荷实验中压痕下方的微观结构进行了事后表征。对于较小的最大压痕载荷，载荷-位移数据表现出相当大的伪弹性恢复，而较高的压痕载荷与卸载后更明显的残余变形相关。这些差异显然与压头尖端以下的微观结构变化有关：虽然通常都会发生应力诱导的马氏体转变和位错滑移，但较高的最大载荷与塑性变形的增加相关。相应的较高位错密度阻碍了向奥氏体的逆转变。对于高压痕载荷，可以在表面正下方观察到稳定的马氏体。我们的结果表明，NiTi 的纳米压痕可以系统分析塑性变形和应力诱导转变为马氏体的相互作用。
The continuous measurement of loads and displacements during nanoindentation of shape memory alloys allows a detailed investigation of pseudoelasticity on the nano-scale. However, the resulting load-displacement data simultaneously reflect several elastic and inelastic deformation processes (i.e., stress-induced martensitic transformation, plastic deformation). In the present study, we perform microstructural investigations in order to analyze the complex interactions between these mechanisms in a Ni-rich alloy. The microstructures below indents from experiments with different maximum indentation loads are characterized post-mortem by transmission electron microscopy. For small maximum indentation loads, load-displacement data exhibit considerable pseudoelastic recovery, whereas higher indentation loads are associated with a more pronounced residual deformation after unloading. These differences are clearly related to microstructural changes below the indenter tip: While both stress- induced martensitic transformation and dislocation slip occur in general, higher maximum loads are associated with an increase in plastic deformation. The corresponding higher dislocation densities impede the reverse transformation to austenite. Stabilized martensite can be observed directly below the surface for high indentation loads. Our results show that nanoindentation of NiTi allows a systematic analysis of the interaction of plastic deformation and stress induced transformation into martensite.