Preparation and mechanical performance of ductile C_sf/Al₂O₃-BN composites - Part 2: Effects of fiber contents and ablation properties

In this paper, ductile C_sf/Al₂O₃-BN composites were prepared by hot-press sintering. Effects of fiber contents on the mechanical performance and ablation behavior of the composites were investigated systematically. The results showed that all the composites fractured in non-brittle failure mode, exhibiting elastic region and non-linear region as shown in load-displacement curves. With the increase in fiber contents from 15 to 30 vol%, mechanical properties of the obtained composites first increased, reached the peak values at fiber content of 25 vol% and then decreased. When being exposed to high-speed oxyacetylene combustion flow for 60 s, the composites with fiber contents of 15, 20 and 25 vol% showed comparable ablation property and mass loss of 5.3, 7.2 and 8.4×10^-4 g/s, respectively. The ablation mechanisms include fiber and ceramic matrix oxidation, decomposition of mullite, evaporation of both B₂O₃ and SiO₂, and mechanical exfoliation.