High-pressure torsion-induced phase transformations and grain refinement in Al/Ti composites

High-pressure torsion (HPT) deformation of multiphase metallic systems produces a high density of interfaces and leads to atomic mixing between the constituent phases. Here we present a study of the interphase boundary structure, grain size evolution and intermetallic phase formation during HPT deformation of a nano-crystalline Al/Ti composite. High-resolution transmission electron microscopy was used to study the structural features of the interphase boundaries. The Al/Ti interphase boundaries were found to significantly promote the generation of dislocations during deformation. After HPT deformation to a shear strain of 87, the average grain sizes of Al and Ti are 22 and 31 nm, respectively. The chemical mixing between the Al and Ti phases was enhanced by defect-mediated short circuit diffusion and dislocation shuffle-controlled plastic deformation at the interphase boundaries. The intermetallic phases formed during HPT deformation are associated with the strain energy stored by the high density of dislocations at the interphase boundaries.