Transition in material removal behavior during repeated scratching of optical glasses

When indented or scratched, ceramics and glasses often exhibit distinct transition(s) in behavior as a function of the load on the abrasive or depth of its penetration. This behavior has important practical consequences in both material fabrication and wear. For example, so-called ductile mode grinding is dependent on reducing the depth of cut below a critical value so that a relatively damage free and smooth surface is produced. Transitions in behavior have been extensively studied using indentation and scratching on polished surfaces. However, in most practical wear, grinding, and polishing applications, scratching actually occurs on surfaces with existing damage.In this study the behavior of three different optical glasses during repeated low-load scratching with a Berkovich diamond indenter is reported. A distinct transition point, corresponding to a change from ductile grooving to chipping along the scratch track, was observed as a function of the number of repeated passes (scratches). The critical number of passes was dependent on both the applied load and the material. Several different methods for identifying the transition point were studied and found to give consistent results.