Processing stainless steel fibre reinforced NiAl matrix composites by reactive hot pressing

Stainless steel fibres (SSF) were first wound and then plated with electrical nickel film. Alternative layers of these properly spaced Ni-coated stainless steel fibres (SSF–Ni) and aluminum foils were then stacked and diffusion bonded at 500 °C, 100 MPa in vacuum for 10 min to produce an SSF–Ni–Al precursor. Lower-temperature reactive hot pressing (RHP) at 700 °C, a process employed in this work, allowed the nickel and aluminum to react to form an NiAl matrix at a temperature approximately 500 °C lower than that accomplished by hot pressing, hot extrusion or hot isostatic pressing (HIP). RHP at 650 °C was also undertaken in order to investigate the mechanism leading to the formation of a nickel aluminide matrix composite. A dense specimen with complete NiAl reaction was obtained by hot pressing at 900 °C. The variance in microstructure that resulted from the different conditions of heat treatment and hot pressing was analysed by optical microscopy, scanning electron microscopy and X-ray diffraction (XRD).