Growth mechanism and mechanical property of laminar iridium coating by electrodeposition

Abstract

Iridium coatings were prepared on rhenium coated graphite by electrodeposition. The Ir coatings were annealed at 1250°C, 1600°C and 1950°C for 7.5h, respectively. Growth mechanism and mechanical properties of the Ir coatings were investigated. Results showed that the as-received Ir coatings had thickness of about 0.25mm and characterized as laminar columnar grain structure, which resulted from using higher and lower current densities (−50mA/cm2 and −20mA/cm2) alternately. Annealing temperature affected mechanical properties of the Ir coating by changing residual stress, defects and grain size of the coating. The average tensile strength of the as-received, 1250°C-annealed, 1600°C-annealed, 1950°C-annealed (in vacuum) Ir coating and 1950°C-annealed (in hydrogen) was about 250MPa, 270MPa, 234MPa, 117MPa and 91MPa respectively.