Microstructure and mechanical properties of continuous Al₂O₃ fibre reinforced Ni₄₅Al₄₅Cr_7.5Ta_2.5 alloy (IP75) matrix composites

Abstract

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.

Acknowledgements

The authors acknowledge the financial support of the Deutsche Forchungsgemeinschaft through the collaborative research centre SFB 561: ‘Thermally Highly Loaded Porous and cooled Multi-layer Systems for Combined Cycle Power Plants’. We also highly appreciate the technical support from our colleagues T. Burlet and Dipl.-Ing. S. Bhaumik in the fabrication of the composites.