Microabrasion of glass – the critical role of ridge formation

Microabrasive wear testing of materials has been the subject of a significant amount of research as its potential for examining the wear behaviour of thin coatings and bulk materials in a sensitive manner has become apparent. The test comprises of rotation of a ball (with no translation) against a testpiece with a pool of abrasive slurry surrounding the contact. While the test is elegant and simple, there are some phenomena which may occur during a test which may render the results of such an abrasive test invalid. This paper has examined the role of ridge formation in soda–lime glass. Ridges are thin bands of unabraded material which form in the wear scar which, if stable, are worn down only by a sliding action against the ball. It is proposed that the ridges form in the wear scar due to inhomogeneous flow of abrasive slurry. Ridge formation is promoted by high loads and low slurry viscosities, both of which hinder entrainment of abrasive particles between the ball and specimen in the early stages of wear and also hinder entrainment of particles between the ball and any existing ridge. A regime where formation of stable ridges is suppressed has been identified in terms of applied load and slurry viscosity for a range of abrasive slurries. Stable ridge formation results in low wear rates, but when ridge formation is suppressed, wear of glass has been observed to be broadly independent of slurry viscosity and proportional to applied load. It is proposed that ridge formation is a general phenomenon in such tests, and care must be taken to ensure that it is suppressed to allow valid abrasive wear tests to be conducted.