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

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 L2(1-)Cu(2)AlMn 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 [901] 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%.