A New Method to Increase the Spheroidization Rate of Lamellar α Microstructure during Hot Deformation of a Ti–6Al–4V Alloy

Ti–6Al–4V is one of the important materials for manufacturing critical components of aero‐engines. The excellent service properties of aero‐engines are dependent on components and their material microstructures. The spheroidization of a lamellar α microstructure is one of the important methods to refine grains in Ti alloys. Herein, a new method is proposed to increase the spheroidization rate of the lamellar α microstructure during hot deformation of a Ti–6Al–4V alloy. The spheroidization behaviors of the lamellar α microstructure are investigated by one‐pass and two‐pass hot compression tests. A special spheroidization behavior, which is defined as metadynamic spheroidization, is found during inter‐pass; i.e., the lamellar α phase breaks up during the inter‐pass due to the migration and transformation of sub‐boundaries. The spheroidization rate of the lamellar α phase is increased by the metadynamic spheroidization mechanism. The effects of inter‐pass holding time, pre‐strain, and total strain on the spheroidization rate are obvious. Furthermore, the spheroidization rate of lamellar α phases by two‐pass compression is approximately 30% higher than that by one‐pass compression for a given total strain of 1.2. In addition, the strains for the completed spheroidization can be effectively reduced by two‐pass isothermal compression.