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

Formation and evolution of new a grain boundary and its influence on globularization behavior of alpha 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 alpha grains firstly increases and then decreases with increasing strain rate and height reduction at a deformation temperature of 740 degrees C. The increasing annealing temperature is beneficial for fragmenting a 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 alpha lamellar interiors are dependent on the strain rate, height reduction and heat treatment conditions. The formation and evolution of new alpha grain boundary during the globularization process are described as follows: (i) the loss of coherency of alpha/beta interphase and the process of dislocation accumulation; (ii) the rotation of different parts in alpha lamellae caused by activated slip system; (iii) the increase of misorientation between alpha 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. (C) 2020 Elsevier B.V. All rights reserved.