Compressive creep properties and mechanisms of (Ti-Zr-Nb-Ta-Mo)C high entropy ceramics at high temperatures

Abstract

The compressive creep properties of (Ti-Zr-Nb-Ta-Mo)C high-entropy ceramics (HEC) and TaC were studied at temperature range of 1400–1600 °C with stresses of 200–300 MPa. Microstructure changes were investigated by transmission electron microscopy (TEM). It is found that the HEC has a higher creep resistance than TaC at 1400–1600 °C. The steady-state creep rates of the HEC are 2.13 × 10−8–2.74 × 10−6 s−1. The stress exponent n of the HEC is 2.76 at 1600 °C and the creep activation energy Q is 486.3 kJ/mol at 200 MPa, higher than that of TaC. The creep mechanisms of the HEC are dislocation motion, grain boundary sliding and atom diffusion. Strain whorls, grain boundary gap and complex dislocation configuration were generated within the crept HEC. The Burgers vectors of dislocations in (Ti-Zr-Nb-Ta-Mo)C is identified to be a2[11̅0]. The increment of TaC grain size is about 2 times of that of (Ti-Zr-Nb-Ta-Mo)C at 1600 °C/200 MPa. The atom diffusion is less active in (Ti-Zr-Nb-Ta-Mo)C than in TaC because of sluggish lattice diffusion in the HEC.