Long-term high-temperature oxidation of iridium coated rhenium by electrical resistance heating method

Abstract

A continuous and compact iridium (Ir) coating with a thickness of ~100μm was electrodeposited on a rhenium (Re) rod in molten salt at 580°C for 4h. The oxidation resistance and failure mechanism of the Ir coated Re (Ir/Re) material were investigated by resistance heating method at 2000°C in air till the Ir coating failed. The results showed that the lifetime of the Ir/Re rod oxidized at 2000°C in air was 183min. After high-temperature oxidation, except for the failure position, the Ir coating in most of the heated regions kept dense and exhibited excellent adhesion on the substrate, with smooth surface and large grain size. The preferred orientation of the Ir coating changed from <220> to <111> after oxidation test. From the end to the center of the as-oxidized Ir/Re sample, the Ir coating became thinner, and the diffusion layer between Ir and Re got thicker. Meanwhile, the preferential oxidation of grain boundaries of Ir coating was more and more severe. It was found that the lifetime of the Ir/Re material in high-temperature oxidizing environment is closely related to the consumption rates of Ir coating by both the direct oxidation of Ir and the diffusion of Re into Ir coating. Based on the diffusion and oxidation kinetics of Re and Ir, the lifetime of the Ir/Re sample in the present study was calculated to be 242min. The difference between the calculated and real lifetimes can be attributed to the ignored fact that Re diffuses rapidly along the grain boundaries of Ir coating in the calculation.