Enhancing the thermal stability and recoverability of ZrCu-based shape memory alloys via interstitial doping

ZrCu-based shape memory alloys (SMAs) are regarded as emerging smart materials with high phase transformation temperatures. However, unfavorable thermal stability and poor strain recovery rate hinder commercial applications. Herein, these issues were addressed by doping interstitial B atoms, and the impacts of B content on microstructure, martensitic transformation behavior and properties of ZrCu-based SMAs were systematically investigated. It was shown that (Zr₅₀Cu₂₅Ni_7.5Co_17.5)_99.98B_0.02 SMAs possessed excellent thermal stability and shape memory effect. The change of martensitic transformation temperature for this alloy was 15.7 °C after several cycles. The shape recovery rate reached 92.5 % at 8 % compressive pre-strain, which was attributed to the de-twinning of (0 0 1) compound twins and the appearance of (1 1 1) type I twins. Furthermore, it was elucidated for the first time by first-principles calculations that B atoms were covalently bonded with Zr and Cu atoms occupying the octahedral interstitial positions in the B19′ and Cm phases. This study offers an available pathway to exploit efficient and advanced products.