Effect of metal diffusion barrier on thermal stability of metal-coated carbon fibers

Abstract

The thermal stability of carbon fibers coated with different metals was investigated. The fracture strength of metal-coated carbon fibers was measured at room temperature as a function of heat-treatment temperature. It was demonstrated that the fracture strength of the copper-coated carbon fibers (C/Cu) was not affected by heat-treatment at temperatures up to 900°C because of the inert of copper. However, the fracture strength of the carbon fibers coated with an active metal (nickel, iron and chromium) were found to decrease significantly after heat-treatment at temperatures >700°C, owing to graphitization (induced by nickel) of the carbon fibers or a chemical reaction (between fibers and iron or chromium) at the interface. A diffusion barrier layer between the active metal coating and the fibers can reduce the strength loss of the carbon fibers, but the effectiveness of a metal diffusion barrier differed depending significantly on the nature of the introduced metals. It was found that if the diffusing active metal had an adequate solubility in a metal, the latter can effectively hinder the diffusion of the former; if not, the latter can not effectively hinder the diffusion of the former.