Retained strength of UHTCMCs after oxidation at 2278 K

•Studied the strength retention of 4 classes of UHTCMCs after oxidation at 2000 °C in air.•Short fibre based UHTCMCs showed the highest strength retention, >80%•For long fibre reinforced UHTCMCs, strength retention was proportional to the UHTC content.•All ZrB2-based UHTCMCs withstood severe temperatures with a good degree of strength retention. In the frame of Horizon 2020 European C3HARME research project, the manufacture of ZrB2-based CMCs was developed through different processes: slurry infiltration and sintering, radio frequency chemical vapour infiltration (RF-CVI) and reactive metal infiltration (RMI). To assess the high temperature stability, room temperature bending strength was measured after oxidizing the samples at 2278 K and compared to the strength of the as-produced materials. Microstructures were analysed before and after the thermal treatment to assess the damage induced by the high temperature oxidation. Short fibre-reinforced composites showed the highest retained strength (>80%) and an unchanged stress–strain curve.