Fabrication and evaluation on thermal stability of hafnium diboride matrix composite at severe oxidation condition

Two hafnium diboride based composites, respectively, containing 20 vol%SiC and 20 vol%SiC-10 vol%AlN, were hot-pressed. Microstructures and mechanical properties were investigated and the thermal stability over 2000 °C was evaluated by oxyacetylene torch. Results indicated that the addition of AlN greatly improved the powder sinterability by eliminating the oxygen contamination. The mechanical properties for HfB₂-SiC-AlN composite, especially the flexural strength were enhanced remarkably through the improvement in density and the formation of AlN-SiC solid solution. Oxyacetylene ablation results indicated that the addition of AlN also improved the thermal stability of composite under severe oxidation conditions. The ablation behavior was investigated and the ablation mechanism was discussed.