Study On Structure And Oxidation Properties Of Iridium-Zirconium Coating On Molybdenum Substrate

In this work, double glow plasma technique was used to produce Iridium-Zridium （Ir-Zr） coatingson Molybdenum （Mo） substrates. In addition, Ir-Zr coatings were obtained on graphite substrates bydouble glow plasma as well, which was presented as a comparison test. The microstructure and themorphology of the coatings were investigated by scanning electron microscope and X-ray diffraction,respectively. The root mean square roughness of the coating was measured by atomic forcemicroscopy. The chemical composition of the coatings was examined by X-ray photoelectronspectroscopy. The mechanical properties of the coatings on the substrates were measured by thescratch testing and nanoindendation, respectively. The residual stresses in the Ir-Zr coatings on Mosubstrates were measured using X-ray diffraction technique. The oxidation performance of Ir-Zrcoating was evaluated by the oxidation furnace. Ir-Zr gradient coating was obtained successfully onthe Mo substrate by double glow plasma. The Ir-Zr coating was generally dense and homogeneous.The coating was composed of a polycrystalline structure with grain size of100nm compared withpure Ir coating. Compared with preferential growth orientation of （220） crystal plane of Ir coating, theIr-Zr coating had a random orientation structure. The RMS roughness value of the Ir-Zr coating is19.3nm, which was lower than the roughness value of45nm for Ir coating. The decrease of theroughness value in the Ir-Zr coating was due to the additional Zr. The Ir-Zr coating with the thicknessof5.0μm was composed of two distinct layers. The proportion of Ir decreased gradually from thesurface of the coating to the coating/substrate interface. The adhesive force of the Ir-Zr coating was15N. The Ir-Zr coating adhered weakly to the substrate due to the formation of the brittle oxide ZrO₂phase on the surface of the coating. The compressive stress in the Ir-Zr coating on Mo was-0.89GPa.The compressive stress in the Ir coating was0.88GPa. The hardness and elastic modulus of the Ir-Zrcoating on Mo were about8.9GPa and397GPa, respectively. It might be inferred that the decrease ofthe hardness was due to the proportion of the Zr element. Because of the information of oxide, such asZrO₂, MoO₃, some pores and the rumpling appeared on the coating after oxidation at600oC,800oCand1000oC, the integrality and adhesion of the coating on the substrate kept up. The proportion of theelements had some changes at different temperatures. The Ir and Zr distribution decreased in thecoating while the Mo and O increased.