APPLICATION OF DIFFUSION-BARRIERS IN COMPOSITE-MATERIALS

Application of diffusion barriers in composite materials is discussed from the point of view of thermodynamic and kinetic stability of the r einforcement/matrix interface. Two types of interface protective coati ng, i.e. inert diffusion barriers and reactive diffusion barriers can be distinguished. The application of one coating or the other depends on the type of damage the material suffers as a result of the interfac e reactions. A double-coating concept for SiC fiber-reinforced titaniu m matrix composites (TMC) is discussed from the viewpoint of this clas sification of diffusion barriers. implication of the C/TiB2, coating s ystem for SIC fiber-reinforced TMC is considered in detail, and some a pproaches to improve the performance of this coating were suggested an d examined experimentally with TiB2, coatings produced by magnetron sp uttering deposition from a TIE, target. The effect of the composition and the microstructure on barrier properties of TiB2 layers was examin ed. A crystalline microstructure with relatively large grains and of s toichiometric composition was found to be optimal for TiB2 protective coatings in SIC fiber-reinforced TMCs. A strong impact of layer stoich iometry on the diffusion of metal atoms through a crystalline TiB2 lay er was found. However, stoichiometry did not significantly affect the diffusion of carbon. Crystalline TiB2, of proper stoichiometry can pro vide excellent protection for carbon coated (SCS6) SiC fibers in titan ium aluminide based metal matrix composites (MMC). (C) 1998 Elsevier S cience S.A. All rights reserved.