Formation and evolution of new α grain boundary and its influence on globularization of α lamellae in TC17 alloy

Formation and evolution of new α grain boundary and its influence on globularization behavior of α lamellae in TC17 alloy with a basketweave microstructure during elevated temperature deformation and subsequent heat treatment are quantitatively investigated using electron backscatter diffraction (EBSD) technique. The results show that the volume fraction of recrystallized α grains firstly increases and then decreases with increasing strain rate and height reduction at a deformation temperature of 740 °C. The increasing annealing temperature is beneficial for fragmenting α lamellae into nearly equiaxed grains due to enhanced termination migration. Based on the analysis of the distribution of in-grain misorientation axe and Schmid factor, it is concluded that the operating slip systems in the α lamellar interiors are dependent on the strain rate, height reduction and heat treatment conditions. The formation and evolution of new α grain boundary during the globularization process are described as follows: (i) the loss of coherency of α/β interphase and the process of dislocation accumulation; (ii) the rotation of different parts in α lamellae caused by activated slip system; (iii) the increase of misorientation between α grains and the formation of LABs; (iv) the formation of HABs; (v) separation of grain boundary; (vi) completion of globularization process via the termination migration.