Investigation on the effect of silicon-graphite and polyimide coating on the wear behaviour of SS304

Abstract

Air foil bearings (AFB) working on hydrodynamic lubrication are exposed to more wear during start-stop condition of motion. To reduce the wear and to improve the damping properties of the top foil, the influence of the combined effect of silicon-graphite coating on bottom side with plain, texture and polyimide (PI) coated surface on top side of stainless steel (SS304) was analysed for low speeds. The SS304 is taken as a foil material on which silicon-graphite mixture is applied at the bottom of all specimens. The other side of the foil is exposed to sliding contact, three different surfaces such as plain, textured and PI coated surfaces are used in this study. Wear behaviour is analysed using pin-on-disc test as per ASTM standard and the results are compared. The average wear loss is 50% lesser in PI coated specimen than the plain specimen. The silicon-graphite coating acted as damper and provide better hardness. The X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, optical microscopy and scanning electron microscopy (SEM) study were carried out to understand the crystalline phase, functional groups, wear track, and wear region on the sliding surface of the specimen respectively. It is observed from FTIR results that the C = O and N-H bonds around 1729 and 3137 cm−1 wavelength. The XRD reveals that the coating shows austenite, martensite and hexagonal crystalline structures. The SEM images show a well adhered structure of PI with SS304. The combination of PI and silicon-graphite coating gives better wear resistance and damping resistance.