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 ZrC_x ceramics. Nano‐hardness values of ZrC_x are reported to be 21‐31 GPa as “x” was varied from 0.5 to 1.0. However, indentation modulus for all ZrC_x compositions remained at ~350 GPa. Microhardness of the ZrC_x increased from 13 to 15 GPa as the stoichiometry was increased from 0.5 to 1.0. The indentation fracture toughness for ZrC_0.5 was 4 MPa m^1/2, and for ZrC_0.67 it was reduced to 3.6 MPa m^1/2. The 3‐point flexural strength for ZrC_0.5 was determined to be 386 ± 26 MPa, which decreased to 316 ± 20 MPa as the carbon content (ZrC_0.67) was increased. The dry sliding wear of ZrC_0.5 to ZrC_0.6 indicated that the coefficient of friction was increased from 0.73 to 0.86 at 5 N load and 500 m sliding distance. Further, ZrC_0.67 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.