Influence of spark plasma sintering and subsequent hot rolling on microstructure and flexural behavior of in-situ TiB and TiC reinforced Ti6Al4V composite

Powder mixture consisting of Ti6Al4V and B4C was sintered at 1100 °C by spark plasma sintering (SPS) to produce Ti - alloy matrix composite reinforced by in-situ TiB whiskers (TiBw) and TiC particles (TiCp). The reinforcement content was chosen in the range of 0.5-2 vol% TiBw and 0.12-0.5 vol% TiCp. In order to investigate the effect of hot deformation on microstructure and mechanical properties of the composites, hot rolling was performed at 900 °C with 66% reduction ratio. The microstructure parameters such as lamellar colony size, alpha layer thickness and aspect ratio of whiskers were measured using image analysis. The results showed refinement of alternate α/β lamellae and alignment of TiBw in rolling direction of the rolled samples. Three-point bending test results showed that among the sintered samples, the Ti6Al4V-0.5 vol% TiBw-0.12 vol% TiCp sample gained the highest flexural yield strength, equal to 1850 MPa. After hot rolling with 66% reduction, the maximum flexural strength reached 2100 MPa in Ti6Al4V-1 vol% TiBw-0.23 vol% TiCp composite. Fractography of the composite samples processed by SPS showed that clustering of whiskers caused a reduction in flexural strength at higher reinforcement contents.