High-temperature deformation behavior and recrystallization mechanism of a near beta titanium alloy Ti-55511 in β phase region

Abstract

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis were performed to investigate high-temperature deformation behavior and recrystallization mechanism of Ti-55511 alloy in β phase region. The stress-strain curves, calculated activation energy and microstructure characterization show that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main soften mechanisms. DRX becomes more significant with decreasing strain rate and increasing deformation temperature and true strain. Recrystallization grains are identified by calculated grain orientation spread (GOS). It is found that quantitative microstructural characteristics, such as DRX volume fraction and DRX grain size, are strongly dependent on process parameters. The discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging and continuous dynamic recrystallization (CDRX) by progressive sub-grains rotation are observed in the deformed microstructure of Ti55511 alloy. The flow softening rate and kinetics exponent of DDRX are higher than those of CDRX. With increasing deformation temperature, DRX mechanism has transformed from DDRX to CDRX, resulting in the unexpected decrease of DRX kinetics exponent nD and flow softening rate. The ηbcc fiber, εbcc fiber and ξbcc fiber are the dominant texture component in deformed Ti–55511 alloy. The weakening of the deformation texture is accompanied by the occurrence of DRX, which can be attributed to the random orientation distribution of DRX grains.