SPUTTER DEPOSITED BARRIER COATINGS ON SIC MONOFILAMENTS FOR USE IN REACTIVE METALLIC MATRICES .1. OPTIMIZATION OF BARRIER STRUCTURE

In a number of metal matrix composite systems, there is a need to combat interfacial chemical attack and other forms of microstructural degradation. There is interest in producing thin surface coatings on (fibrous) reinforcements, to act as diffusion barrier layers or to otherwise modify the surface characteristics. An assessment of relevant factors is presented in terms of thermodynamic, kinetic and mechanical considerations. Possible advantages of a "duplex", metal/metal oxide double layer, are examined with particular reference to a titanium matrix. Two procedures are described for the production of such barriers on SiC monofilaments using sputter deposition, one a batch process and the other involving continuous production. The effect of deposition conditions is considered in terms of optimising barrier structure.