Effect of initial microstructure and beta phase evolution on dynamic recrystallization behaviour of Ti6Al4V alloy - An EBSD based investigation

Abstract

The use of Ti6Al4V alloy in critical aerospace applications among other titanium alloys is higher due to the high strength, toughness and corrosion resistance characteristics. Achieved combination of strength and toughness is directly related to the bimodal (equiaxed alpha plus transformed beta) microstructure obtained by hot working of this alloy in a narrow strain rate and temperature domain. Present study distinctly describes the evolution of microstructure during hot deformation as an effect of process conditions and initial microstructure characteristics of Ti6Al4V alloy. The initial microstructure and processing conditions significantly influenced the evolution of β phase and dynamic recrystallization behaviour. An increase in β phase fraction was observed due to the increased adiabatic temperature at higher strain rates during α+β working. The increase in volume fraction of stable β phase as result of vanadium diffusion during hot working revealed the existence of strain induced phase transformation. Continuous dynamic recrystallization (CDRX) led to the fragmentation of initial α grains, and the effect of initial grain orientation on the CDRX mechanism was studied. The initial grains with the basal plane parallel to the compression direction revealed large fragmentation due to the high resistance to deformation. A CDRX mechanism map was developed based on the effect of processing conditions and initial grain characteristics.