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A Review on Micro-mechanical Testing of NiTi-Based Shape Memory Alloys
Journal
Journal of the Indian Institute of Science
ISSN
09704140
Date Issued
2022-01-01
Author(s)
Kumar, S. Sujith
Arohi, Adya Charan
Sen, Indrani
Abstract
NiTi-based shape memory alloys are considered as potential candidates for various structural, functional and biomedical applications. This is particularly related to their unique characteristics such as pseudoelastic and shape memory effects. Considering the increasing demand of NiTi alloys in miniaturized devices, the small-scale deformation micro-mechanisms of such a material system is being thoroughly reviewed in this article. At the first hand, the fundamental characteristics of NiTi system is discussed briefly. The influence of different factors such as chemical composition, crystallographic phases and precipitates on the phase transformation and mechanical behavior of the material are emphasized next. Subsequently, an extensive overview is provided regarding the assessment of small-scale deformation behavior of NiTi alloys using two prime techniques: micro-pillar compression and instrumented nanoindentation. Pros and cons for both the characterization techniques are analyzed as well. Interestingly, uniaxial compression of the micro-pillar reveals the pseudoelastic behavior in the alloy with remarkable enhancement in martensitic transformation stress and plateau strain with respect to those observed from macro-scale testing. It is also evident from the studies that mechanical behavior of the material strongly depends on different crystallographic orientation. Contrary to the uniaxial compression, nanoindentation generates triaxial state of stress beneath the tip of indenter, which is likely to influence the deformation micro-mechanism for the NiTi system, as well. Variation in hardness, elastic modulus and recoverability of NiTi system are primarily assessed through nanoindentation-based studies. In addition, recent studies highlight the importance of optimizing the nanoindentation parameters such as tip configuration, tip radius and load level for precise estimation of pseudoelastic activity in the alloy. Moreover, a simplified approach is generated for estimating the indentation stress–indentation strain curve. Overall, this paper generates a thorough and comprehensive insight about the micro-mechanical testing of NiTi-based shape memory alloys.
Volume
102