Fabrication and mechanisms of densification of ZrB₂-based ultra high temperature ceramics by reactive hot pressing

Abstract

Dense ZrB₂-SiC (25-30 vol%) composites have been produced by reactive hot pressing using stoichiometric Zr, B₄C, C and Si powder mixtures with and without Ni addition at 40 MPa, 1600 °C for 60 min. Nickel, a common additive to promote densification, is shown not to be essential; the presence of an ultra-fine microstructure containing a transient plastic ZrC phase is suggested to play a key role at low temperatures, while a transient liquid phase may be responsible at temperatures above 1350 °C. Hot Pressing of non-stoichiometric mixture of Zr, B₄C and Si at 40 MPa, 1600 °C for 30 min resulted in ZrB₂-ZrC_x-SiC (15 vol%) composites of ~ 98% RD.