Development and characterisation of novel ceramic-metal composites

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Ceramic-metal composites (or cermets) combine the favourable mechanical properties of both constituents, namely the high hardness and wear resistance of ceramics and the ductility and toughness associated with metals. Consequently, cermets are used in diverse applications including: transportation (marine, automotive, aerospace), chemical processing, pulp and paper processing, waste incineration, etc.. For many decades tungsten carbide/cobalt 'hardmetals' (WC/Co) have been the primary example of industrially applied cermets. However, these materials are limited in application by their poor resistance to corrosion and high temperature oxidation (i.e. above ~500°C), as well as their susceptibility to high temperature strength degradation. Recently, a new generation of advanced cermets, based on either carbide or boride ceramics combined with ductile nickel or iron aluminides, has been developed in work conducted by the applicant. In particular, titanium carbide/nickel aluminide (TiC/Ni3Al) cermets exhibit generally similar mechanical properties to WC/Co at room temperature, but vastly superior elevated temperature behaviour. For example, it has been demonstrated that TiC/Ni3Al cermets are actually stronger at 1000°C than at room temperature, while they also have less than half the mass of WC/Co. In the proposed work, novel variants of these materials will be developed, based on alloyed titanium carbonitride (Ti(C,N)) matrices, as well as nano-structured TiC matrices. Fundamental studies of the wetting and melt-infiltration behaviour will be conducted to assess processing parameters. The contact fatigue response of the composites will be determined under Hertzian indentation loading conditions, at both room and elevated temperature. A novel method based on focused ion beam excision of the indented regions will be developed to assess elastic/plastic deformation. The oxidation behaviour will be determined using thermogravimetric analysis and microstructural characterisation. In addition, novel binders will be evaluated, with a preliminary screening conducted using sputtering based combinatorial search methods, combined with nano-indentation of the resulting libraries.