Densification, mechanical, and tribological properties of ZrB2-ZrCxcomposites produced by reactive hot pressing

ZrB2-ZrC(x)composites were produced using Zr:B4C 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 degrees C for 60 minutes. X-ray diffraction analyses confirmed the formation of nonstoichiometric zirconium carbide (ZrCx) 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:B4C composition from 86% to 99%. Microstructural studies on Zr-rich composites showed a reduction in unreacted B4C particles and enriched elongated ZrB(2)platelets. Reaction and densification mechanism in 4Zr:B4C composition were studied as a function of temperature increased from 600 to 1200 degrees C at an applied constant pressure of 7 MPa. After 1000 degrees 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 ZrB2-ZrC(x)composite. The results clearly showed that the applied pressure is five times lower than the reported values. Moreover, a temperature of 1200 degrees C was sufficient to produce dense ZrB2-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 x 10(-2)mm(2)/N, respectively.