Superior superplasticity and multiple accommodation mechanisms in TiB reinforced near-α titanium matrix composites

Abstract

Superplastic forming is a promising technique for producing complex-shaped components of hard-to-deform titanium matrix composites (TMCs). Superplastic tensile tests were performed on hot-rolled TiB/near-α Ti matrix composites with different reductions to investigate the effects of matrix microstructural characteristics and whisker orientation on superplastic deformation behavior. The results showed that the composite with initial BT-type texture and finer matrix grains at a rolling reduction of 80% exhibited lower flow stress and larger elongation than the composite with initial T-type texture at a rolling reduction of 40%, and superior elongation of 682% was achieved in the former. Significant randomization of crystal orientation and dynamic grain growth phenomenon occurred in the matrix alloys during deformation. The originally misaligned TiB whiskers gradually rotated to the tensile direction and simultaneously rotated circularly around the [010] axis during superplastic tensile deformation, which would accommodate the matrix deformation and share more load transferred from the matrix. Another important accommodation mechanism of TiB whiskers was to accelerate the dynamic recrystallization of the surrounding matrix by particle-stimulated nucleation. TEM and EBSD observations together with GND-distribution analysis confirmed that the primary superplastic deformation mechanism of TiB/Ti composites is grain/phase boundary sliding accommodated by dislocation slip and dynamic recrystallization.