Ultrastrong Ti–6Al–4V composite with hierarchical microstructure through two-step ball milling and pressureless sintering

Abstract

We report a new hierarchical microstructure in ultrastrong Ti–6Al–4V composite with TiC reinforcement via pressureless sintering. Specifically, powder sintered contained pre-introduced nano TiC particles, which were generated by first ball milling of blended powders of 60Al40V medium and minor Ti and subsequent ball milling with cyclohexane. The hierarchical microstructure consisted of primary thick β-Ti laths surrounding coarse equiaxed α-Ti zones, which consisted of cellular structures with ultrafine equiaxed α-Ti matrix and nano/ultrafine β-Ti lamellar. Essentially, the hierarchical microstructure originated from the nano TiC particles inhibit β-Ti grain growth and provide nucleation sites for α-Ti grains. Surprisingly, the hierarchical composite exhibits ultrahigh tensile yield strength, far superior to those of Ti–6Al–4V alloy and its composites by sintering. Fundamentally, the hierarchical microstructure and interface S-phase layers containing stacking faults were responsible for the ultrahigh yield strength. The results provide a new strategy to fabricate ultrastrong Ti matrix composites for demanding structural application.