Diffusivity of carbon in copper- and silver-based composites

Interstitial solid solutions could be formed at the matrix-fibre interface in the processing of metal matrix composites. Typically these solutions are of small concentrations and the solubility is usually diffusion-controled. To calculate the diffusivity, a model of the interstitial solid solution i s used which gives the possibility of choosing whether octahedral or tetrah edral interstitial positions are occupied by the fibre atoms dissolved in t he matrix. Analysis of Ag-C and Cu-C solid solutions allow a comparison of the occupation of the interstitial positions and its temperature dependence s. The results obtained on the basis of non-empirical calculations predict the preferable occupation of octahedral positions up to T similar to 1200 K . This confirms the structure of the interstitial solid solution. In the fr amework of this model we calculate the heights of diffusion barriers and th e temperature dependences of carbon diffusion in silver and copper hosts. ( C) 1999 Kluwer Academic Publishers.