Abnormal grain growth in annealing cast Cu–Al–Mn–V alloys and their superelasticity

Abstract

Metals are usually difficult to fabricate bulk materials with a large grain size over cm-scale only through heat treatment with neither directional solidification nor macroscopic deformation. This paper reports a novel method to obtain large grains and single crystals over cm-scale only through simply annealing polycrystalline cast Cu–Al–Mn–V shape memory alloys. The results show that the abnormal grain growth (AGG) directly occurs when cast alloys are annealed at 1173 K, and ultra-large grains and single crystals are obtained after quenching. The AGG results from unique microstructure of cast Cu–Al–Mn–V alloys. All cast alloys consist of L21-Cu2AlMn parent and completely coherent bcc A2(V) nanoparticles due to bcc phase separation. The results further show that the dissolution of A2(V) nanoparticles into the matrix during annealing results in a continuous misorientation gradient within the matrix grains. It may provide the driving force for the rapid migration of grain boundaries, leading to the AGG. Furthermore, the single crystals close to exhibit good superelasticity. Cu-13.7Al-8.6Mn-1.4 V single crystal shows the largest full superelasticity of 7.0%, and Cu-13.2Al-9.8Mn-0.7 V single crystal exhibits the largest superelastic strain of 5.4%.