The Role of Diffusion in Corrosive Wear

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Abstract
Oxygen diffusion through the lubricant film is an important factor in corrosive wear, a type of wear where the primary attack is the formation of iron oxide at the rubbing surface. Experimental data were obtained in a ball-on-cylinder device and quantitatively correlated with oxygen availability by a mathematical model. This model assumes two parallel surfaces separated by a small distance, one surface moving with respect to the other. The lubricant at the inlet is saturated with oxygen, which diffuses to the stationary surface to form iron oxide. The iron oxide is removed immediately by the rubbing motion. From the analysis the average clearance predicted was about 10 microinches, a reasonable figure. For the condition used experimentally, essentially all of the oxygen entering the system will diffuse to the surface and be consumed. Thus, differences in mass diffusivity are not important in determining the wear rate. The experimental observations, in agreement with the theoretical prediction, show that corrosive wear increases with oxygen concentration and sliding speed.