Study on Microstructure and Properties of (TiC+TiB)/ Ti-6Al-4V Composites

The (TiC+TiB)/Ti-6Al-4V composites with reinforcement volume fractions of 0, 1% and 5% are prepared by in situ synthesis and powder metallurgy, and the microstructures and properties of the composites are analyzed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). It is found that the Ti-6Al-4V composite consists of plate-like α phase and β phase interspersed between α phases. The α phase in the (TiC+TiB)/Ti-6Al-4V composite transforms into an equiaxed structure, and its length is reduced by 85.10% compared to that of the plate-like one in the Ti-6Al-4V composite, indicating that the reinforcements have a grain-refining effect. The tensile strengths of the (TiC+TiB)/Ti-6Al-4V composites are higher than that of the Ti-6Al-4V composite, and the higher the volume fraction of the reinforcement, the higher the tensile strength of the composite. The tensile strength of the reinforced composite with 5% of reinforcement is 15.54% higher than that of the composite without reinforcement. The percentage elongation after fracture of the composite decreases with the increase of the volume fraction of the reinforcement. The overall mechanical properties of the composite with 3% of reinforcement is the optimal. All the four types of the composites exhibit brittle fractures. Large TiB reinforcements are observed to be pulled out, leaving cavities, while no debonding of fine TiB reinforcements is found. Therefore, controlling the size of TiB reinforcements within a certain range can effectively enhance the mechanical properties of titanium matrix composites, which provides theoretical foundation and technical guidance for the application of the titanium matrix composites.