Functional Fatigue of NiTi Shape Memory Alloy: Effect of Loading Frequency and Source of Residual Strains
Functional Fatigue of NiTi Shape Memory Alloy: Effect of Loading Frequency and Source of Residual Strains
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DOI：
10.1007/s40830-022-00397-8
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发表时间：
2022-11
影响因子：
2.2
通讯作者：
R. Sidharth;A. Mohammed;H. Sehitoglu
中科院分区：
文献类型：
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作者：
R. Sidharth;A. Mohammed;H. Sehitoglu
由于潜热释放和随之而来的热机耦合，NiTi SMA 具有高度的速率敏感性。本研究探讨了疲劳载荷下加载频率对超弹性镍钛合金功能特性的影响。研究了沿“<011>”和“<001>”加载方向压缩的单晶的弹热温度变化、正向/反向转变应力、残余应变积累和滞后之间的变化和相互作用。结果表明，由于滞后现象减少，NiTi 的功能在较高加载频率下更好，并且功能退化与奥氏体域中相变诱导的塑性有关。 TEM 研究揭示了相变引起的平行位错不仅存在于广泛报道的滑移系统中，而且存在于滑移系统中。这些位错的来源分别通过晶格对应追溯到马氏体对应变体对 (CVP) 的 II 型和 I 型内部孪晶。此外，观察到这些位错在沉淀物-B2界面处堆积并激活沉淀物中的滑移和/或剪切。这是以前从未报道过的另一种功能退化和耗散机制。
Due to latent heat release and the consequent thermomechanical coupling, NiTi SMAs are highly rate sensitive. In this study, the effect of loading frequency on the functional characteristics of superelastic NiTi is explored under fatigue loading. The variation and interplay between the elastocaloric temperature change, forward/reverse transformation stresses, residual strain accumulation and hysteresis were studied for single crystals compressed along the <011> and <001> loading orientation. It is shown that the functionality of NiTi is better at higher loading frequency due to reduced hysteresis and the functional degradation is linked to transformation induced plasticity in the austenitic domains. TEM investigation reveals transformation induced parallel dislocations not only on the widely reportedslip system but also on theslip system. The source of these dislocations is traced to the type II and type I internal twins of the martensite correspondent variant pair (CVP) via lattice correspondence, respectively. Moreover, it was observed that these dislocations pile-up at the precipitate-B2 interface and activate slip and/or shear into the precipitates. This is yet another functional degradation and dissipative mechanism that has not been reported before.