Martensite stabilization in bulk metallic glass composites with shape memory crystals

Abstract

The stress-induced martensitic transformation in “martensitic” or “shape memory” bulk metallic glass composites (BMGCs) plays a pivotal role in enhancing their plasticity and work-hardening capability. However, limited attention has been paid to the martensite stabilization in such BMGCs. This work investigated the effect of deformation and annealing on the reversibility of the martensitic transformation in shape memory BMGCs using experiments and simulations. It is found that the martensitic transformation from B2 to B19 ´ during mechanical loading becomes progressively more irreversible with increasing the strain. A large contribution to this effect can be ascribe to the stress field induced by the shear band formation, in accordance with the finite element simulation showing that residual stresses in the composites suppress the reverse transformation after deformation. Annealing the deformed composites above the glass transition temperature (Tg) relaxes the residual stresses, and the phase transformation becomes again fully recoverable. These results may have important implications for controlling the microstructure and mechanical properties of the shape memory BMGCs during thermomechanical treatments.