Large [001] single crystals via abnormal grain growth from columnar polycrystal

Abnormal grain growth induced by cyclic heat treatment for unidirectionally solidified Cu–Al–Mn shape memory alloys was investigated by electron backscatter diffraction. A Cu–17.5Al–11Mn (at%) alloy was initially fabricated by unidirectional solidification, showing [001] textures along the solidification direction with columnar grains and a high fraction of low-angle grain boundaries. Abnormal grain growth was then involved using cyclic heat treatment for the columnar polycrystal, during which the subgrains that formed because of precipitation served as a strong driving force. The migration of high-angle grain boundaries dominates the abnormal grain growth behavior, and no orientation deviation occurs during cyclic heat treatment so the large grains or single crystals maintain a [001] orientation. With repeated cyclic heat treatments, single-crystalline Cu–17.5Al–11Mn (at%) alloys showing [001] orientation with dimensions of 50 mm × 10 mm × 1 mm could be obtained, in which an excellent recoverable strain of more than 10% was observed.