Microstructural characterization and mechanical properties of TiC/near-α Ti composite obtained at slow cooling rate

Abstract

In this paper, microstructural characterization and mechanical properties of 10vol% TiC/Ti-6Al-3Sn-3.5Zr-0.4Mo-0.75Nb-0.35Si composite obtained at slow cooling rate has been discussed. Equiaxed or near-equiaxed α phase was formed in the composite when cooled from above the β-transus temperature at a cooling rate of 10°C/min. This is due to the fact that α precipitates can heterogeneously nucleate on TiC particles during the slow-cooling process. It was obtained that the lattice disregistry between TiC and α precipitates was only 3.8%, which corresponds to the crystallographic orientation relationship of [2-1-10]α//[011]TiC; (0001)α//(1-11)TiC. The tensile results showed that heat treatment improved UTS and elongation, simultaneously, below 700°C. The enhancement of UTS is mainly attributed to solid solution strengthening of C in matrix since about 5.5vol% TiC dissolved into matrix after heat treatment. The obvious increase in room-temperature elongation is because of the formation of equiaxed microstructure and the reduction in the sizes of spheroidised TiC particles. With the increase of temperature, the discrepancy in UTSs of the as-cast and heat-treated composites became small.