Comparative Investigation of Iridium Coating Electrodeposited on Molybdenum, Rhenium and C/C Composite Substrates in Molten Salt in the Air Atmosphere

Iridium coatings were prepared on molybdenum, rhenium and C/C composite substrates by electrodeposition in molten salt in the air atmosphere, respectively. The iridium coatings on both the molybdenum and C/C substrate are defective and the adhesion is quite poor, while the iridium coating on rhenium substrate is adhesive and compact without any defects. The microscopic surface morphologies of the iridium coatings obtained on different substrates appear highly similar. The preferred growth directions of the iridium coatings on the rhenium and C/C composite substrates are <111> and <311>, respectively, while the iridium coating on molybdenum substrate has a polycrystalline structure without a certain preferred orientation. The adhesion and surface quality differences of iridium coating obtained on the various substrates arise from different corrosion behaviors in molten salt in the air atmosphere and surface characteristics of the various substrates.