A FUNCTIONALLY GRADIENT COATING ON CARBON-FIBER FOR C AL COMPOSITES/

A functionally gradient coating on carbon fibre for casting C/Al compo sites with an ultimate tensile strength up to 1250 MPa (V(f) = 0.35) h as been produced. The coating consisted of three layers: an inner pyro carbon layer, an outer silicon layer and an intermediate gradient laye r C/SiC/Si, and their optimum thicknesses were 0.1-0.15, 0.1 and 0.2 m um, respectively. This coating was fabricated by chemical vapour depos ition and the C/Al composite was performed by pressure-regulated infil tration. Auger electron spectroscopy and X-ray diffraction analyses co nfirmed that the structure of the coating was in keeping with its desi gn. The excellent ultimate tensile strength of the C/Al composite also proves that the functionally gradient coating has many functions, inc luding wetting agent, diffusion and reaction barrier, releaser of resi dual thermal stresses, and tailor of interfacial shear strength. Accor ding to the mechanical, physical and chemical coordination between fib re and matrix, the functionally gradient coating can solve nearly all the problems of the interface during fabrication and service.