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.