Improving sinterability of Ti-6Al-4V from blended elemental powders through equal channel angular pressing

Ti-6Al-4V billets were fabricated from a blend of commercially-pure titanium (CP Ti) and a master alloy (Al60V40) powders, using equal channel angular pressing (ECAP) as a tool for powder consolidation. The density of the compact in excess of 99% was achieved at a sintering temperature that was markedly lower than the temperatures reported for conventional blended elemental (BE) powder routes. A detailed electron microscopy investigation was employed to analyse the microstructures of the powder compact and account for its improved sinterability. The results indicated that the intense shear imposed by ECAP has generated localised strain heterogeneities in the CP Ti particles along with {101̄1}α-type mechanical twins. Shear-assisted elimination of Ti oxides on the powder particle surface gave rise to direct bonding between the Ti phases. While powder particles of CP Ti and master alloy were always separated by an interfacial oxide layer, interdiffusion of Al and Ti atoms was detected by STEM-EDX, which indicates the existence of diffusion bonding between unlike particles. The roles of severe plastic deformation in the evolution of interfacial and lattice structures of the powder particles are discussed with regard to the enhanced compaction and sintering performance.