Antiphase boundary-like structure in α″ martensite of TC21 titanium alloy

The morphology and formation mechanism of the substructure of martensite in TC21 alloy was investigated by XRD and TEM. The results showed that the martensitic transformation from β to α″ occurs upon quenching after solution treatment between 960-1000 °C. The antiphase boundary (APB)-like structure was observed clearly in the α″ martensite plates. The APB-like contrasts exist along the (001) and (020) planes of α″ martensite. This APB-like structure of α″ martensite was identified as a kind of stacking fault with an APB-like morphology induced by martensitic transformation and not by order/disorder transition. During martensitic transformation, martensitic domains nucleate and grow, eventually encounter each other, resulting in the formation of the APB-like contrast.