R.f. magnetron sputtered iridium coatings on carbon structural materials

R.f. magnetron sputtering was used to produced iridium coatings on carbon-carbon composite and isotropic graphites (coefficient of thermal expansion (CTE) approximately (0.92-7.6) × 10^-6 K^-1) at room temperature and 1073 K. Sputtered iridium coatings exhibit a homogenous surface irrespective of the deposition temperature. Extremely fine grained columnar structures of iridium were observed when deposited at room temperature. Compared with room temperature deposition, substrate firing at 1073 K produced denser coatings with less strains and larger grain size. Cracking was observed on the coating deposited at 1073 K in the case of c-c composite and isotropic graphite with a thermal expansion coefficient of approximately (0.92-4.8) × 10^-6 K^-1. For iridium coatings deposited onto isotropic graphite (CTE approximately 7.6 × 10^-6 K^-1) at 1073 K, after heat treatment at high temperatures in N₂, there was no cracking, no outward diffusion of carbon, no dislocations and pores were reduced or eliminated.