Improved pseudoelasticity behavior of NiMnGaDy shape memory alloys via thermal-mechanical training

Abstract

Considerable interest in improving the mechanical properties and functional performance such as the pseudoelasticity behaviors of NiMnGa shape memory alloys (SMAs) was stimulated by their technological applications in transducers, aerospace and solid-state refrigeration. This study presented a novel approach to enhance the mechanical and pseudoelasticity behaviors of the polycrystalline NiMnGa SMAs by combining Dy micro-alloying and thermal-mechanical training. The results showed that DyNi₄Ga precipitation after Dy addition contributed to alloy's excellent ultimate strength (∼1506.9 MPa) and elongation to fracture (∼17.5%). With the aid of thermal-mechanical training, pseudoelastic recovery strains reached 3.5 times those of untrained alloys, which was attributed to the development of preferential variants and the broadening of the stress gap between the yield stress for plastic deformation and the critical stress for phase transformation.