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

In this research, TaC-HfC-VC system composites were hot pressed with the addition of nanographiteand nano-carbon black particles in different ratios as a sintering aid in order to improvethe densification and mechanical properties such as fracture toughness and consequently thermalshock resistant. The hot pressing of the composites was carried out at of ۱۷۰۰, ۱۸۰۰, ۱۹۰۰ and۲۰۰۰ ºC for ۴۵ min under a uniaxial pressure of ۴۰ MPa. The physical and mechanical propertiesof the composites including relative density, porosity, Vickers hardness and fracture toughnesswere measured. Microstructural investigation and phase analysis of the polished and fracturesurfaces of the hot pressed samples were also carried out. The hot pressed composites had ahomogeneous microstructure and there was no detectable impurity in the mixing process. Therewas a significant grain growth in the microstructure of pure TaC sample. SEM micrographs andXRD patterns of the hot pressed samples indicated the formation of a solid solution betweencarbides and thus formation of a single phase microstructure. Also, the addition of nano graphiteand nano carbon black particles the densification of composites improved and a relative densityof ۱۰۰% was achieved. The addition of hafnium carbide and vanadium carbide increased theVickers hardness of the TaC from ۱۵ GPa up to ۲۳ GPa and fracture toughness of ۵.۴ MPa.m۱/۲was obtained. By increasing the hot pressing temperature, due to the grain growth, a decrease inthe hardness and fracture toughness of the composites were observed.