Ultra-high temperature deformation in TaC and HfC

TaC and HfC bars were thermo-mechanically tested up to 2900 degrees C using a non-contact loading method based on the Lorentz force. It was observed that HfC deflected more than TaC up to 2300 degrees C, which has been contributed to a difference in grain size facilitating diffusional creep, either Nabarro-Herring or Coble creep. Above 2500 degrees C, TaC continued to deflect more with temperature whereas HfC showed a reduced deflection. This reduced deflection was found to be an artifact of a preload plastic deformation response. Though both sets of samples were identified to have a prevalence of < 110 > {110} slip, at elevated temperatures, it appears that mass transport and diffusional creep mechanisms dominate evident by porosity in the grain boundaries. The activation energies of TaC were found to be 946 +/- 157 kJ/mol (between 2500-2700 degrees C) and HfC to be 685 +/- 54 kJ/mol (between 2100-2300 degrees C).