Dependence of Nano-Friction and Nano-Wear on Loading Force for Sharp Diamond Tips Sliding on Si, Mn-Zn Ferrite, and Au

Microscopic friction and wear were measured on both the original top surfaces and freshly worn surfaces of three solid materials including a silicon wafer, a Mn-Zn ferrite block and an Au film, using a recently developed scanning probe microscope with sharp diamond tips. A critical point was observed on the friction versus normal loading force curve. The critical point divides the friction curve into two distinct regimes: a low friction regime in which the friction coefficients are from 0.03–0.06, and a high friction regime where the friction coefficients are between 0.12 and 0.38 depending on the materials tested and the tips. The critical loads at the critical points are different for different materials and different tips. But the average pressures corresponding to the critical points calculated by the Hertz elastic contact theory for different tips are close to each other for the same material. The freshly worn surfaces have tribological behaviors similar to those of the corresponding original top surfaces. Below the critical load no wear is detectable, whereas above the critical load wear is obtained with the wear depth proportional to the load. The implications are that a no-wear sliding condition is possible, for example in contact recording systems, if the asperity contact loads all remain less than the critical value for the particular sliding system.