Microstructure and mechanical properties of continuous Al₂O₃fibre reinforced Ni₄₅Al₄₅Cr_7.5Ta_2.5alloy (IP75) matrix composites

Single crystalline Al2O3 fibres (sapphire), coated with the NiAl alloy IP75 by physical vapour deposition (PVD), were assembled to fabricate composites by means of diffusion bonding. The microstructure and chemistry of both as-coated fibre and as-diffusion bonded composites were investigated by electron microscopy and microanalysis. The interface shear stress for complete debonding was measured by fibre push-out tests at room temperature, and the composite tensile strength was measured at 900°C and 1100°C. An amorphous layer with a thickness of about 400 nm formed between the fibre and the matrix during the PVD process and was maintained during diffusion bonding. A Laves phase precipitated along NiAl grain boundaries in the IP75 matrix. This caused a lower tensile strength of the IP75/Al2O3 composite at high temperatures compared to as-cast monolithic IP75 and rendered the composite useless for structural applications.