High-temperature diffusion in couple of chemical vapor deposited rhenium and electrodeposited iridium

•Grain boundaries of Ir coating provide short circuit paths for the diffusion of Re.•The calculated diffusion activation energy is 1.38 eV for diffusion of Re into Ir.•The calculated lifetime of Ir/Re (50 μm-thick Ir coating) operated at 2200 °C is 21 h.•The hardness of the Re zone is not affected by high-temperature annealing.•The Young's modulus of different zones increases after high-temperature annealing.

The iridium coated rhenium (Ir/Re) combustion chamber, allowing hours of operation up to 2200 °C, offers the thermal margin for high performance and extended lifetime for radiation-cooled rockets. Its lifetime is closely related to the high-temperature diffusion between Ir and Re. For the purpose of predicting and improving the performance limit of the Ir-coated Re thruster, the diffusion kinetics of Ir/Re, prepared by electrodeposition in molten salt and chemical vapor deposition (CVD) respectively, was studied in the temperature range of 1800 to 2200 °C using the semi-infinite diffusion model for the diffusion of Re into Ir. The microstructure and elemental concentration of the Ir/Re samples before and after the high-temperature annealing treatment were determined by optical microscope, environmental scanning electron microscope (ESEM) and electron probe micro-analyzer (EPMA). The diffusion coefficients and activation energy were calculated based on the experimental results. It was found that the grain boundaries of the Ir coating provide short circuit paths for the diffusion of Re into Ir. The mechanical properties of the Ir–Re diffusion couple including hardness and Young's modulus were also studied before and after high-temperature treatment.