Low-energy irradiation induced giant quasilinear superelasticity over wide temperature range in NiTi shape memory alloys

Abstract

Continuous strain glass transition (STGT) in shape memory alloys (SMAs) has attracted much attention and shows potential applications in biomedical, robotics, and micro-electromechanical systems due to its quasilinear superelasticity (SE). However, the reported strain glass system in NiTi alloys through doping antisite point defects can only produce local $R$-phase martensitic domains and show small recoverable strain ($\ensuremath{\sim}1%$), which limits its wide applications. Here, we propose a method to design B19\ensuremath{'} strain glass with large recoverable strain in NiTi binary alloys by introducing interstitial atoms and vacancies through low-energy irradiation by integrating molecular dynamics and phase field modeling. The interstitial atoms play the most important role to transform the normal martensitic transformation (MT) to STGT. A complete phase diagram is established to describe the relationship between MT/STGT and irradiation energy. The system after large irradiation energy $(\ensuremath{\sim}5.3\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.16em}{0ex}}\mathrm{keV}/\mathrm{c}{\mathrm{m}}^{2})$ has shown obvious frequency dependence of storage modulus, continuous volume fraction change, and B19\ensuremath{'} martensitic nanodomains, which confirm the existence of B19\ensuremath{'} STGT. This B19\ensuremath{'} strain glass has shown large recoverable strain $(\ensuremath{\sim}5.8%)$ over a wide temperature range (from 100 to 300 K), which can be attributed to the continuous nucleation and growth of martensitic nanodomains in this temperature range. Our calculations theoretically proposed a method to design strain glass systems with giant quasilinear SE by interstitial defects and may stimulate the application of SMAs.