Effect of nonstoichiometry on mechanical properties of reactive hot‐pressed monolithic ZrCx Ceramic

The reactive hot pressing (RHP) of Zr:C powder mixture at various molar ratios (1:0.5, 1:0.6, and 1:0.67) at applied pressures of 4‐7 MPa and 1200°C resulted in dense ZrCx ceramics. Nano‐hardness values of ZrCx are reported to be 21‐31 GPa as “x” was varied from 0.5 to 1.0. However, indentation modulus for all ZrCx compositions remained at ~350 GPa. Microhardness of the ZrCx increased from 13 to 15 GPa as the stoichiometry was increased from 0.5 to 1.0. The indentation fracture toughness for ZrC0.5 was 4 MPa m1/2, and for ZrC0.67 it was reduced to 3.6 MPa m1/2. The 3‐point flexural strength for ZrC0.5 was determined to be 386 ± 26 MPa, which decreased to 316 ± 20 MPa as the carbon content (ZrC0.67) was increased. The dry sliding wear of ZrC0.5 to ZrC0.6 indicated that the coefficient of friction was increased from 0.73 to 0.86 at 5 N load and 500 m sliding distance. Further, ZrC0.67 showed a reduction in friction coefficient of 0.81, and this was due to the increase of strong Zr–C covalent bond and unreacted graphite.