Effects of cathodic current density and temperature on morphology and microstructure of iridium coating prepared by electrodeposition in molten salt under the air atmosphere

Iridium coating was prepared on a Re/C substrate (graphite substrate coated with rhenium coating by CVD) using electrodeposition in molten salt of chlorides in the air atmosphere. The effects of cathodic current density and temperature on both the morphology and microstructure of the coating were studied, respectively. The morphology and orientation of the coating were determined by scanning electron microscope and X-ray diffraction, respectively. The results showed that the cathodic current density and temperature both affected the surface morphology, roughness, grain size and compactness of the iridium coating. With increasing of current density from 5 to 50 mA/cm2, the surface roughness of the coating increased from Ra 0.98 to Ra 6.29 μm, while the grain size decreased. With temperature increasing from 520 to 640 °C, the surface roughness of the coating decreased from Ra 4.41 to Ra 1.16 μm, while the grain size increased. The preferred orientations of the coatings changed in the row <111>–<220>–<311> with current density increasing. With the increase of temperature, the preferred orientation of the coating changed from <1 1 1> to <2 2 0>, and again to <1 1 1>. The coating with <1 1 1> orientation was smoother and denser than that with <2 2 0> orientation regardless of the grain size.