Synthesis and densification of (Zr-Hf-Nb-Ta)C-Co high entropy cermet prepared by pressureless melt infiltration using spark plasma sintering

Novel (Zr-Hf-Nb-Ta)C-xCo (x = 5, 10, 20 wt%) high entropy cermets (HEC4-Co) were successfully synthesized and densified using a simple two-step high temperature process. The high entropy carbide was first synthesized by solid state reaction at 1800 ℃ of a mixed powder compact. The reacted and partially sintered compact was then pressureless melt infiltrated with cobalt at 1600 ℃. The results show that degassing of the powders in the first step, before the infiltration step, significantly reduced the defects in the cermets. The HEC4-Co cermets consisted of a single-phase high entropy carbide (Zr-Hf-Nb-Ta)C in a single-phase cobalt matrix. The maximum hardness was achieved for a Co content of 10 wt%, 15.38 GPa (1569HV1), while the cermet with a Co content of 20 wt% had the highest indentation crack resistance, 9.72 MPa m1/2.