LEO space environment exposure resistant behavior of Ag–Cu films

Abstract

Ag–Cu films, deposited by arc ion plating and composed of face-centered cubic (fcc) Ag and AgCu alloy phases, had been exposed for 43.5h in low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard the China Shenzhou-7 manned spaceship. The structure, morphology, composition and tribological property of the Ag–Cu films after the space environment exposure (SEE) were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS) and ball-on-disk tribometer, respectively. After the SEE, the surface layer of Ag–Cu film was partially oxidized to Ag2O, in which the Ag2O content was decreased from the surface to inner and the Cu element was absent. Furthermore, the exposed Ag–Cu film surface became color and exhibited lots of fine particle-like protuberances, but cracking and flaking phenomena that were common for the exposed Ag film, were not observed. Overall, the influence of space exposure on Ag–Cu film was slight compared to the pure Ag film. Sliding friction tests revealed that for the exposed Ag–Cu film, the friction coefficient was stable and the mean value was almost equivalent to one of the non-exposed Ag–Cu film.