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

Abstract

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.