Sintering behaviour, solid solution formation and characterisation of TaC, HfC and TaC-HfC fabricated by spark plasma sintering

Solid solution formation and sintering behaviour of TaC-HfC ceramics made from commercial TaC and HfC powders prepared using spark plasma sintering (SPS) at temperatures up to 2450 °C was investigated. Phase analysis and lattice parameter measurements using X-ray Diffraction (XRD) showed mutual diffusion of Hf and Ta with increasing sintering temperature. High Resolution Transmission Electron Microscopy (HRTEM) confirmed that solid solution formation and densification were achieved by a solid-state mechanism. Solid solutions were achieved for 4TaC-1HfC, 1TaC-1HfC and 1TaC-4HfC powders after sintering at temperatures of at least 2350 °C. Fracture toughness (KIC) values were in the range of 2.7-3.4 MPa m1/2 for all ceramics measured using Vickers indentation. Thermal conductivity of TaC was 55.8 W/m K at 1400 °C. Coefficients of thermal expansion (CTE) varied from 7.08-7.66 × 10−6/K (in the range of 25-2000 °C), with TaC at the lower end.