Oxide-fibre/nickel-based matrix composites—part I: fabrication and microstructure

The only monocrystalline oxide fibre that has been used in numerous published works on oxide-fibre/Ni-based-matrix composites is sapphire fibre. That work was aimed at obtaining small numbers of samples to study microstructure and the strength of the fibre/matrix interfaces. The present work aims at (i) the fabrication of a series of composite specimens for the first stage of a systematic mechanical testing of heat-resistant composites, and (ii) a study of the macro- and microstructure of composites with various oxide fibres and nickel-based matrices. Hundreds of specimens of oxide-fibre/Ni-based-matrix composites were obtained. Three types of fibre, sapphire, monocrystalline yttrium–aluminium garnet and alumina–garnet eutectic, and two matrices, a Ni3Al-based γ′/γ alloy and a modern nickel γ/γ’ superalloy, are used in all six combinations. The fibres are produced by the internal crystallisation method, such fibres being sufficiently inexpensive to be used to reinforce nickel-based alloys manufacturing composites by the pressure-infiltration route. It is shown that a sufficiently homogeneous fibre distribution in a cross-section of the composite sample can be achieved. The microstructure of the fibre/matrix interface, studied by means of optical and scanning/transmission electron microscopy is found to be extremely sensitive to a combination of the fibre and matrix materials.