Investigating Microstructure, Physical and Mechanical Properties of TaC-HfC-VC System Composites

In this research, TaC-HfC-VC system composites were hot pressed with the addition of nano-graphite and nano-carbon black particles in different ratios as a sintering aid in order to improve the densification and mechanical properties such as fracture toughness and consequently thermal shock resistant. The hot pressing of the composites was carried out at of 1700, 1800, 1900 and 2000 ºC for 45 min under a uniaxial pressure of 40 MPa. The physical and mechanical properties of the composites including relative density, porosity, Vickers hardness and fracture toughness were measured. Microstructural investigation and phase analysis of the polished and fracture surfaces of the hot pressed samples were also carried out. The hot pressed composites had a homogeneous microstructure and there was no detectable impurity in the mixing process. There was a significant grain growth in the microstructure of pure TaC sample. SEM micrographs and XRD patterns of the hot pressed samples indicated the formation of a solid solution between carbides and thus formation of a single phase microstructure. Also, the addition of nano graphite and nano carbon black particles the densification of composites improved and a relative density of 100% was achieved. The addition of hafnium carbide and vanadium carbide increased the Vickers hardness of the TaC from 15 GPa up to 23 GPa and fracture toughness of 5.4 MPa.m1/2 was obtained. By increasing the hot pressing temperature, due to the grain growth, a decrease in the hardness and fracture toughness of the composites were observed.