The effect of heat treatment on the tensile strength of the iridium-coated carbon fiber

Iridium coatings were applied on carbon fibers using metal organic chemical vapor deposition (MOCVD) approach from iridium(III) acetylacetonate as a precursor at reduced and atmospheric pressure. The mechanical properties of the fibers coated by iridium at atmospheric pressure were analogous to those for as-received carbon fibers. For fibers coated by iridium at reduced pressure a decrease of tensile strength was observed because of the penetration of iridium species into a porous structure of carbon filament, the formation of rather strong bonding between iridium particles and carbon support and an appearance of additional stresses. An evolution of the mechanical properties and morphology of the iridium coated carbon fibers with temperature was studied. The comparison of these features before and after the high-temperature treatment indicates that both morphology and mechanical properties are greatly influenced by the high-temperature treatment. A sharp degradation of the mechanical properties of the treated Ir-coated fibers was detected. With increasing temperature, agglomeration of iridium particles into large aggregates of the round-shape form was observed. The heated iridium coatings showed good adherence to carbon fibers and no cracks and spallation of coatings were observed despite of the iridium and carbon coefficient thermal expansion (CTE) mismatch.