Densification, mechanical, and tribological properties of ZrB 2 ‐ZrC x composites produced by reactive hot pressing

ZrB 2 ‐ZrC x composites were produced using Zr:B 4 C powder mixtures in the molar ratios of 3:1, 3.5:1, 4:1, and 5:1 by reactive hot pressing (RHP) at 4‐7 MPa, 1200°C for 60 minutes. X‐ray diffraction analyses confirmed the formation of nonstoichiometric zirconium carbide (ZrC x ) with different lattice parameters and enhanced carbide formation by increasing the Zr mole fraction. An increase in applied pressure from 4 to 7 MPa was responsible for the improved relative density (RD) of 4Zr:B 4 C composition from 86% to 99%. Microstructural studies on Zr‐rich composites showed a reduction in unreacted B 4 C particles and enriched elongated ZrB 2 platelets. Reaction and densification mechanism in 4Zr:B 4 C composition were studied as a function of temperature increased from 600 to 1200°C at an applied constant pressure of 7 MPa. After 1000°C, <40 vol.% of unreacted Zr was observed during the densification process. Concurrently, low energies of carbon diffusion and carbon vacancy formation were found to enhance nonstoichiometric ZrC x formation, which was found to be responsible for the completion of the reaction. The plastic deformation of unreacted Zr was responsible for the densification of the ZrB 2 ‐ZrC x composite. The results clearly showed that the applied pressure is five times lower than the reported values. Moreover, a temperature of 1200°C was sufficient to produce dense ZrB 2 ‐ZrC x composites. The improved microhardness, flexural strength, fracture toughness, and specific wear rate were 8.2‐15 GPa, 265‐590 MPa, 2.82‐6.33 MPa.m 1/2 , and 1.43‐0.376 × 10 −2 mm 2 /N, respectively.