Effect of initial roughness and oxidation on the running-in wear of machined surfaces under dry sliding

It is usually considered that initial roughness of a surface affects running-in wear. Oxidation of the surface is bound to occur during machining operation. The present investigation aims at understanding the influence of initial roughness and surface oxidation on the wear rate. Studies were conducted with a ball-on-flat geometry in a reciprocating tester at room temperature and at 100°C. Flat surfaces with initial roughness values of 0.42, 0.96 and 1.81 µm were used for dry tests of 120 minutes duration. It was observed that running-in wear rates were low and were inversely related to roughness. This phenomenon was explained on the basis of contact temperature rise and oxide thickness. After running-in, all the balls showed wear rates within a range of about 10% from 20 to 60 minutes. The roughness of the flats stabilised in the range of 0.04 µm to 0.06 µm at the end of the test.