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 degrees C and, separately, achieved a toughness of 10 MPa m(1/2). In addition, the composite withstood the ablation effect of an oxyacetylene torch at 2500 degrees 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. (C) 2019 The Authors. Published by Elsevier Ltd.