Grain fragmentation associated continuous dynamic recrystallization (CDRX) of hexagonal structure during uniaxial isothermal compression: High-temperature α phase in TiAl alloys

Dynamic recovery (DRV) and dynamic recrystallization (DRX) of hexagonal materials during hot deformation is a sub-domain of restoration processes, which has not well been addressed. In this work, the DRV and DRX mechanisms of high-temperature α phase in TiAl alloys were thoroughly investigated by microstructural characterization and crystallographic analysis with an extended intragranular misorientation axis (IGMA) analysis method. It was revealed that the nucleation of recrystallized grains experienced three steps: (ⅰ) the occurrence of stress-induced grain boundary bulging and the formation of symmetrical-tilt low-angle boundaries characterized by 〈0001〉 disorientation axis induced by prismatic <a> slip; (ⅱ) the evolution of the low-angle boundaries into asymmetrical-tilt boundaries characterized by 〈101¯x〉 disorientation axis by local basal <a> slip, or tilt-twist boundaries characterized by 〈112¯y〉 disorientation axis through rotational grain boundary sliding, resulting in the formation of subgrains from the boundary bulges; (ⅲ) the detachment of the subgrains and the mixing of the detached subgrains by grain boundary sliding. These three steps happened continuously and repeatedly from the boundary regions toward grain interior till the completion of recrystallization. This work provided original information of continuous DRX (CDRX) of hexagonal materials. The extended IGMA method developed in this study is helpful for related investigations.