REACTION-BONDED REFRACTORY-METAL CARBIDE CARBON COMPOSITES

A simple chemical process has been developed that allows the rapid con version of carbon substrates to the refractory metal carbides (MC) of titanium, zirconium, hafnium, vanadium, niobium, tantalum and tungsten . As a demonstration of the technique, graphite rods are infiltrated w ith an ethanolic solution of various metal oxide-halides, and resistiv ely fired (1350-3000-degrees-C) under an argon atmosphere. The final c omposite produced is found to contain a residual carbon core within a fully dense metal carbide-carbon matrix outer layer. The effects of bo th firing temperatures, and the number of infiltration-fire treatments , have been investigated in order to determine optimum firing conditio ns (i.e. maximum carbide formation) for each individual metal carbide. To demonstrate the applicability of the technique for a range of subs trate materials, niobium and titanium carbides were formed on carbon f ibre tows and non-porous substrates, respectively. The formation of mi xed Nb-Ti carbide coatings of varying composition were investigated in order to determine the factors controlling the formation of ternary p hases. The identity of the transition metal precursors and the possibl e pathway of their conversion to the appropriate carbide is discussed. All the composites have been characterized by X-ray photoelectron spe ctroscopy (XPS), scanning electron microscopy (SEM) with associated en ergy-dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD).