Merging toughness and oxidation resistance in a light ZrB₂ composite

A functionally graded composite based on ZrB₂ and 0–50 vol% of short carbon fibres was prepared via a deliberately simple approach that involved creating a suitable stacking sequence of layers with different sintering agents and fibre contents. This led to an excellent combination of failure tolerance and oxidation resistance in a light material with a density below that of alumina. The graded architecture outperformed other related composites when tested at 1500 °C and, separately, achieved a toughness of 10 MPa m^½. In addition, the composite withstood the ablation effect of an oxyacetylene torch at 2500 °C, undergoing minimal recession. Moreover, the true nature of the “tubular” zirconium oxide formed upon oxidation at extreme temperatures is reported for the first time. The functionally graded concept applied to a ultra-refractory matrix seems to be a promising route to obtain even complex shaped components with functional symmetry for use in severe environments.