Transformation Temperature Predictions Through Computational Intelligence for NiTi-Based Shape Memory Alloys
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TECHNICAL ARTICLE
Transformation Temperature Predictions Through Computational Intelligence for NiTi-Based Shape Memory Alloys Yun Zhang1
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Xiaojie Xu1
Received: 6 July 2020 / Revised: 18 September 2020 / Accepted: 30 September 2020 Ó ASM International 2020
Abstract Shape memory alloys (SMAs) are a class of metallic compounds that can return to their original forms, shapes, or sizes, when subjected to environmental stimuli, such as temperature and magnetic fields. Due to their unique shape memory effects and pseudoelasticity, SMAs, particularly NiTi-based ones, are of great interest in structures and composites, electronics, automobiles, biomedicine, and robotics. To tailor phase transformation temperature for practical applications, chemical substitutions have been extensively investigated and utilized. However, with multiple elements substituting for Ni, the correlation between the composition and transformation temperature is not elucidated but only the general trend is revealed with limited doping situations. In this study, we develop the Gaussian process regression model to find statistical correlations between NiTi-based SMAs’ transformation temperature (Tp ) upon heating and nine pertinent physical parameters of alloying elements. More than 50 samples, with Ni partially substituted by one to three elements, are explored for this purpose. The modeling approach shows a high degree of stability and accuracy that contributes to low-cost Tp estimations. Keywords NiTi Materials Shape memory SMA Transformation temperature
& Yun Zhang [email protected] Xiaojie Xu [email protected] 1
North Carolina State University, Raleigh, NC 27695, USA
Introduction The shape memory effect in an equiatomic Ni–Ti alloy was first discovered by Buehler et al. in 1962 [1]. Earlier, a solid-state phase transformation was observed in Au–Cd ¨ lander but was not interpreted [2]. In 1951, alloys by O Chang and Read [3] associated this transformation with an apparent plastic deformation by studying through diffraction measurements. The SME is a diffusionless solid-tosolid transformation between martensitic and austenitic crystal structures, depending on temperature or magnetic fields [4–9]. SMAs are able to recover large, seemingly permanent strains via heating from a deformed shape in martensite to a remembered austenitic one [10]. Due to their unique capabilities, SMAs have been strongly sought in numerous application fields, including automobiles, biomedical implants, structures and composites, actuators, robotics, and micro-electromechanical systems [11–25]. Among the SMAs, Ni–Ti alloys are the most attractive and popular ones due to their superior strength, ductility, biocompatibility, and stability of transformation temperature [26]. Other types of SMAs, such as Fe- and Cu-based alloys, are often viewed as potential cost-effective replacements, which however, may suffer from the phase instability, larger transition hysteresis width, and brittleness as compared to Ni–Ti alloys [27]. Furthermore, the integration of SMAs into
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