RF MAGNETRON-SPUTTERED IRIDIUM COATINGS ON CARBON STRUCTURAL-MATERIALS

R.f. magnetron sputtering was used to produce iridium coatings on carbon-carbon composite and isotropic graphites (coefficient of thermal expansion (CTE) approximately (0.92-7.6) x 10(-6) K(-1)) at room temperature and 1073 K. Sputtered iridium coatings exhibit a homogeneous 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 heating at 1073 K produced denser coatings with less strain 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) x 10(-6) K-1. For iridium coatings deposited onto isotropic graphite (CTE approximately 7.6 x 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.