Reactive hot-pressing of platelet-like ZrB2–ZrC–Zr cermets: Processing and microstructure

Abstract

In this study, two methods of powder reactions and reactive hot-pressing were used for the reaction of Zr+B4C powder mixtures. The powder reactions were performed at various temperatures, between 600°C and 1100°C, to examine the reaction behaviour occurring during the synthesis. To fabricate a cermet composed of platelet-like ZrB2 grains and equiaxed ZrCx grains, with intergranular Zr phase, reactive hot-pressing was conduced within temperature range of 1100–1900°C. The effects of temperature on the reactions, densification behaviour and microstructure of the samples were assessed. For samples sintered at 900°C or above, the Zr+B4C mixture was converted into ZrB2 and ZrCx; the conversion was completed at ~1100°C. Densification resulted from volume contraction due to the conversion of Zr+B4C mixture into ZrB2 and ZrCx, and the shrinkage due to grain boundary diffusion and grain boundary migration. For Zr+B4C mixtures sintered at or above 1400°C, relative densities exceeding 97% were obtained. When sintered at or below 1400°C, the resulting ZrB2–ZrCx–Zr cermet consisted of rod-like ZrB2 grains, equiaxed ZrCx grains and residual Zr. Highly-developed platelet-like ZrB2–ZrCx–Zr cermet was obtained only at sintering temperature of 1600°C or greater.