Microstructure evolution and tribological behavior of the solid lubricant based surface composite of cast nickel aluminum bronze developed by friction stir processing

In the present work, friction stir processing (FSP) of the cast nickel aluminum bronze (NAB) alloy (C95500) and fabrication of graphite reinforced surface composite by means of FSP route have been carried out. Optical microscope (OM) and scanning electron microscope (SEM) were used for the microstructural study. Microstructural observation suggested the presence of a sound processed surface with a fine equiaxed grain in the stir zone (SZ). Microhardness measurement revealed that FSP increases the surface hardness as compared to as-cast surface, as it constitutes of refined grain structure. Wear behavior of the surfaces was assessed by performing sliding wear test on pin-on-disk tribometer. It was found that upon addition of the graphite particles, wear properties were improved by 43.87% and 51.93% in comparison to both FSPed and as-cast surface respectively. The enhanced wear resistance is due to the formation of protective lubricant film between sliding surfaces in case of surface composite. The measurement of stacking fault energy (SFE) by X-ray line profile analysis was carried out and its effect on sliding wear behavior was also studied. The X-ray line profile analysis suggested that FSP results in the decrease of SFE as compared to the as-cast surface.