Study of thermomechanical processing method to promote twins in pure Zr

A thermomechanical processing has been developed to introduce a high density of twins in commercial-purity Zr as a grain boundary engineering approach. With repeated cold working and annealing heat treatment, the fraction of deformation twins reached up to 40%, and accordingly the microstructure was refined. The twins, as analyzed by EBSD, turned out to be mostly {10 1 2}-type or {10 1 1}-type twins, the condition of generation of which is consistent with the criteria of comparatively low twin boundary energy and minimum shear strain. The present result asserts that it is possible to produce a microstructure favorable for the application of the grain boundary engineering in Zr and its alloys of hcp crystal structure like fcc-based metals