Thesis of Firouz Rezaei Babere

An investigation into the effect of various additives on hot pressing of tantalum carbide based composites

By Firouz Rezaei Babere

Supervisor: Dr. M. Gassemi Kakroudi, Dr. M. Rezvani

University of Tabriz

September 2016

Abstract: TaC-based composites were hot pressed with addition of vanadium carbide, 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 resistent. The hot pressing of the composites was carried out at of 1700, 1800, 1900 and 2000 ºC for 45 min under an uniaxial pressur 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. By addition of nano graphite and nano carbon black particles the densification of composites improved and a relative density of 100% was achieved. Addition of hafnum carbide and vanadium carbide increased the Vickers hardness of the TaC from 15 GPa up to 23 GPa.