Multiple scratch tests and surface-related fatigue properties of monolithic ceramics and soda lime glass

In this study, the scratch resistance of several monolithic structural ceramics and soda lime glass was investigated using repeated scratching. Rockwell indentation was used to perform unidirectional multi-pass scratches at progressive loads. It is shown that there is a build up of sample damage as the number of scratches increases, the severity of which being assessed by measuring the depth of the scratches and by performing optical observations of the worn tracks. For each applied load, there is a critical number of passes above which the material removal rate increases dramatically through chipping. By plotting the critical number of passes against the applied load, strength/number of cycles (S/N) like diagrams can be obtained. Although soda lime glass exhibits a lower resistance than most of ceramics for single scratch tests, the glass removal rate becomes similar to that of ceramics when repeated scratch tests are considered. It is suggested that the material resistance to multiple scratch tests rely on the presence of a thin layer of re-compacted and plastically deformed material under the action of the indenter. The absence of such a layer in silicon carbide may explain the surprisingly poor resistance of this material for high applied forces and important number of cycles. It is suggested that this layer improves the material resistance against scratching by decreasing the friction coefficient, thereby diminishing the level of stresses generated within the specimen.