Wear Behavior of Friction Stir Processed NAB Alloys in Marine Environment

Nickel Aluminum Bronze (NAB) alloy specimens subjected to Friction Stir Processing (FSP) with and without particulate addition were subjected to tribological testing in a reciprocating sliding tester which can perform sliding test on specimens immersed in seawater. Stainless steel ball was slid against flat coupons of NAB as cast, and Friction-Stir-Processed NABs, under sea-water to study the wear performance considering their prospective use in marine bearing applications. The wear expressed in terms of the wear scar area measured using an image processing method indicates that the performance of the Friction-Stir-Processed NABs in sea-water environment is inferior to that of the un-processed NAB, even though the processed NABs have relatively superior hardness. While wear tests in dry condition indicate that the wear resistance for the friction stir processed samples is high, under saline environment the trend was found to be reversed, as their wear resistance was found to be low. The reduction in wear resistance in sea-water is explained in terms of the (electrochemical) corrosive wear mode being active in the saline medium. The surface damage as revealed from the SEM characterization of wear scars were found to correlate with the experimental deductions.