Oxidation Resistance Coatings of Ir-Zr and Ir by Double Glow Plasma

Oxidation resistance coatings of Ir-40 at.% Zr and Ir were produced onto Mo substrates by double glow plasma technology. The oxidation resistances of the coatings were evaluated at high temperature. Ir-Zr coating consisted of two layers: the primary layer close to the substrate was composed of dense columnar grains and the second layer was composed of dense grains of nanometric size. The mass gain of Ir coating above 800 °C was about 1.35% due to the formation of solid IrO2. The mass loss of Ir coating was about 5.3% due to the formation of gaseous oxide IrO3 when being held at 1227 °C for 30 min. The substrate was protected more effectively by multilayer than monolayer coating of Ir in oxidizing environment. The Ir-Zr coating was well bonded to the substrate after oxidation at 800 °C. After oxidation at 1000 °C, the Ir-Zr coating was poorly bonded to the substrate. The oxidation resistance of Ir-Zr coating was poor due to high content of Zr.