Influence of roughness on wear transition in glass-infiltrated alumina

The wear behavior of glass-infiltrated alumina was evaluated in sliding against a high-purity alumina in water using a pin on disk tribometer. Three disk Ra roughness values were used, i.e. 14, 146 and 649 nm. The wear rate of both the alumina balls and the glass-infiltrated alumina disks increased with the disk roughness. The steady-state values of coefficients of friction towards the end of the tests were almost the same for the polished and the intermediate roughness surfaces at 0.58 and 0.54. However, the coefficients of friction for the tests with the high roughness disks were reduced to 0.30. A close examination of the friction/time traces showed an abrupt change in the coefficient of friction only for the tests with the high roughness disks. The test duration associated with this transition was reproducible in repeat tests. When this transition occurred, the initial rough surface had been polished to a roughness of 25 nm by wear. The difference in the behavior of the three roughness conditions, and particularly the transition phenomenon in the tests with high roughness surfaces, is discussed in terms of several factors that include three-body “self-polishing”, reduced contact pressure with increased wear, formation of a hydrated layer by tribochemical reaction and associated “hydrodynamic” lift, and presence of grinding-induced residual stresses and subsurface grinding damage.