Evolution of equiaxed and lamellar a during hot compression in a near alpha titanium alloy with bimodal microstructure

Microstructural evolution of equiaxed a and lamellar a during hot compression in a bimodal-structure near alpha Ti-6Al-3Nb-2Zr-lMo alloy were investigated. Focus was concentrated on their own dynamic restoration mechanism via electron backscatter diffraction (EBSD) technique. Based on analysis of grain boundary misorientation distribution and misorientation gradient within a grain, it was revealed that limited continuous dynamic recrystallization (CDRX) as well as adequate dynamic recovery (DRV) took place within equiaxed a, whereas CDRX occurred as the main restoration mechanism in lamellar alpha. Further, the deformation heterogeneous among equiaxed a grains was found to be relevant to the difference in slip systems. Under the same nominal strain of 75% height reduction, process of weak DRV, strong DRV and CDRX coexisted in distinct equiaxed a grains owning to small, medium and high Schmid Factor of prismatic slip. Besides, globularization heterogeneity induced by CDRX in lamellar a was considered to be closely related with its initial orientation to compression axis and the imposed strain. For flat colony a, the microstructure was relatively stable during straining showing a thinning process and a weak dynamic globularization, while the kinked colony a with large strain was globularized sufficiently.