Dynamic recrystallization mechanism and improved mechanical properties of a near α high temperature titanium alloy processed by severe plastic deformation

The effect of deformation temperature on microstructure evolution and mechanical properties of a near α titanium alloy during isothermal multiple die forging (IMDF) is systematically investigated. Present study describes the grain refinement mechanism at different deformation temperature by electron back-scatter diffraction (EBSD) characterization. The results indicated that the grain refinement as a result of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). With the decrease of deformation temperature, the mechanism of DRX converts from DDRX to CDRX. The formation of new grains by CDRX mechanism is mainly attributed to the progressive rotation of sub-grains. Moreover, the fresh grains resulted from DDRX process form along the serrated grain boundaries by bulging. It indicates that the superior tensile strengths of the IMDFed titanium alloy at room temperature (RT) and 650 °C are attributed to grain boundary strengthening and dislocation strengthening. However, grain boundary strengthening no longer works above 650 °C, leading to rapid decreases in tensile strengths.