In situ ZrC/Si-B-C-N monoliths prepared by sol-gel and reactive hot-pressing: Processing, microstructure, mechanical properties and oxidation behavior

Abstract

In this work, in situ ZrC/Si-B-C-N monoliths prepared by sol-gel and reactive hot-pressing techniques were developed. The fine ZrC powders were synthesized by decomposition of zirconium propanol and furfuryl alcohol using as the source of zirconium and carbon, respectively. The as-sintered ZrC/Si-B-C-N monoliths composed of ZrC, SiC and BN(C) with a very fine and homogenous microstructure. The in situ formed ZrC and SiC were equiaxed, whereas the in situ BN(C) was graphic hexagonal with a fake-like structure. Due to the poor sinterability of ZrC, the as-sintered monoliths with relative low densities of <80% were obtained, which was primarily responsible for the poor mechanical performance. ZrC/Si-B-C-N monoliths oxidized at 1500 °C for different time possessed the same oxidation products of ZrO2 and ZrSiO4. SiC and BN(C) oxidation are predicted thermodynamically more strongly than ZrC, which resulted in a thick, uneven, heterogenous and porous oxide scale. The introduction of ZrC weakens the oxidation resistance of Si-B-C-N matrix leading to a continuous weight gain.