b to w phase transformation due to aging in a Ti-Mo alloy deformed in impact compression

We investigated the roles of vacancies and their clusters introduced in a Ti-20mass% Mo alloy by high-speed compression in the formation of aged *w-phase crystals. Specimens were deformed by a static compression mode and a high-speed compression mode, and were then aged. The relationships between morphology of aged *w-phase crystals and deformation modes are discussed along with the roles of vacancies and their clusters in the nucleation and growth of aged *w-phase crystals. Aged *w-phase crystals were found to be smaller but of higher density in a high-speed deformation specimen. These results suggest that vacancies and their clusters easily become nucleation sites of aged *w-phase crystals. Several aged *w-phase crystals in a high-speed deformation specimen were of string-like shape. High-resolution electron microscopy confirmed that the string-like crystals have the *w-phase crystal structure. One of the roles of vacancies of and their clusters introduced by high-speed deformation is considered to be relief of compressive stress, which is predicted to arise in the course of transformation. [Material: Ti-20Mo.]