Oxide-fibre/Ni-based matrix composites—II: mechanical behaviour

The main objective of the present work is to evaluate the high-temperature creep properties of a family of heat-resistant composites. For the first time, it has been possible to test hundreds of specimens of oxide-fibre/Ni-based matrix composites at high temperatures, between 1100 and 1200 °C. The composites were made from three types of fibre (sapphire, monocrystalline yttrium-aluminium garnet, and alumina-garnet eutectic) and two matrices, a Ni3Al-based alloy and a modern nickel superalloy. This has become possible as a result of the availability of substantial quantities of fibres produced by the internal-crystallisation method. Creep resistance of the composites is highly dependent on the interface strength. The interface strength in such composite systems is affected by a large number of factors, e.g. fibre and matrix materials, fibre volume fraction, and fabrication parameters. Values of the interface strength measured in the present work vary from 10 to 300 MPa, but the possibility of reaching higher values should not be excluded. With presently achieved values of interfacial strength, the stress to cause 1% creep strain in 100 h is as high as 270 MPa at 1100 °C and 125 MPa at 1150 °C. This is far beyond the capabilities of non-reinforced nickel superalloys.