Low-Temperature Processing of ZrB2-ZrC Composites by Reactive Hot Pressing
Dense ZrB2-ZrC and ZrB2-ZrCx∼0.67 composites have been produced by reactive hot pressing (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B4C powders at 40 MPa and temperatures up to 1600 °C for 30 minutes. The role of Ni addition on reaction kinetics and densification of the composites has been studied. Composites of ∼97 pct relative density (RD) have been produced with the stoichiometric mixture at 1600 °C, while the composite with ∼99 pct RD has been obtained with excess Zr at 1200 °C, suggesting the formation of carbon deficient ZrC x that significantly aids densification by plastic flow and vacancy diffusion mechanism. Stoichiometric and nonstoichiometric composites have a hardness of ∼20 GPa. The grain sizes of ZrB2 and ZrCx∼0.67 are ∼0.6 and 0.4 μm, respectively, which are finer than those reported in the literature.
The work that has been reported is a result of support from Director, NAL, Head, Materials Science Division, NAL, and a grant to the Indian Institute of Science from the Defence Research and Development Organization. The authors are indebted to Messrs. V. Babu and P.M. Jaman for assistance in hot pressing experiments, Dr. S. Usha Devi for XRD measurements, and Dr. G.S. Avadhani and Mr. Keshab Barai for their assistance in the SEM work.
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