Effect of interphase characteristics on long-term durability of oxide-based fibre-reinforced composites

Mullite based fibre-reinforced composites having double layer fibre-coating s were produced and characterised. The multi-layer inter phases were produc ed by a CVD-process (carbon(fugitive)/ZrO2 or Al2O3) On aluminosilicate Nex tel (TM) 720 fibres. Composites were fabricated by infiltration of coated f ibres with a pre-mullite slurry and hot-pressing in argon at 1300 degreesC. Short term heat-treatment of composites in air yielded a gap between the f ibre and the oxide layer by oxidation of the carbon layer (so-called fugiti ve layer). The composites were statically and cyclically heat-treated at 13 00 degreesC for 1000 h in order to identify the mechanical and microstructu ral changes. Mechanical characterisation of the heat-treated composites was carried out by three-point bending. The effectiveness of the fugitive laye r is determined by the oxide layer and its high-temperature stability in in teraction with the matrix but it also depends on the loading condition. Und er cyclic heat-treatment conditions the composites are found to be more sta ble and damage tolerant than under constant high-temperature exposure. (C) 2001 Elsevier Science Ltd. All rights reserved.