Recrystallization behavior during hot tensile deformation of TA15 titanium alloy sheet with substantial prior deformed substructures

Dynamic recrystallization to a large extent determines the microstructure of near-alpha titanium alloys during the thermo-mechanical processing in alpha + beta two phases zone. And the initial microstructure has a dramatic effect on the recrystallization behavior. Therefore, this paper deals with the recrystallization behavior of a near-alpha TA15 titanium alloy sheet with substantial prior deformed substructures during the annealing and hot tension at 800 degrees C. Undeformed and deformed regions of tensile samples, viz., static recrystallization and dynamic re crystallization, were studied respectively through E13513 observation. It was found that, the unusual intragranular nucleation of discontinuous recrystallization was observed in the relatively coarse grains, which was formed by the enclosed low angle grain boundaries rearranged by the thermally activated recovery. And most of the recrystallized grains manifested as three types of special grain boundaries, namely [0001]30 degrees, [11 (2) over bar0]75 degrees and [13 (8) over bar (5) over bar 3]9 degrees, which showed the cusps in grain boundary energy and can stabilize the recrystallized grain embryo. The substantial prior deformed substructures of the employed TA15 sheet, viz., low angle grain boundaries and dislocations, can facilitate the formation of subgrains and nucleation, which brought about a mixture of continuous and discontinuous recrystallization, regardless of dynamic or static. During the hot tension, the activation of dislocations would accelerate the annihilation and rearrangement of dislocations, thus, recrystallization can take place more frequently, which finally leads to an equiaxed microstructure.