Sputter deposition and film characterization of NiAl on sapphire fibres

Abstract

Once the fibre–matrix bonding has been optimized to meet the different requirements during fabrication and operation of the subsequent composite component, sapphire fibre-reinforced NiAl will be a potential candidate to substitute conventional superalloys as structural material for gas turbine blades. To improve the composite fabrication process, a direct deposition of the intermetallic matrix material onto hBN-coated sapphire fibres prior to the consolidation of the fibre–matrix composite is proposed. It is believed that this will simplify the fabrication process and prevent pore formation during diffusion bonding. In addition, the fibre volume fraction can be quite easily adjusted by varying the NiAl coating thickness. For this, a high-rate deposition of NiAl is in any case necessary. It has been achieved by a pulsed DC magnetron sputtering of combined Al–Ni targets with the fibres rotating between the two facing cathodes. The obtained nickel aluminide coatings were analyzed as to structure and composition by means of X-ray (GIXRD) as well as electron diffraction (RHEED) and X-ray photoelectron spectroscopy as well as electron probe microanalysis, respectively. The morphology of the NiAl coatings was examined by scanning electron microscopy.