Grain size dependence of scratch-induced damage in alumina ceramics

Variable depth single and double scratch experiments were conducted on alumina ceramics of three distinct grain sizes. Utilizing laser profilometry, SEM, and force transducers, an in-depth analysis of volume of material removed, microstructural damage features, and applied force, respectively, was performed as a function of grain size. In single scratches, for a given depth of cut the extent of lateral cracking and material removal volume increased with grain size. In interacting double scratches, a critical separation distance was observed where the extent of damage reached a maximum. For all three grain sizes, the volume of material removed at this critical separation distance reached four times the volume removed by a single scratch. This critical separation distance decreased with decreasing grain size. It was also noticed that the force required to create the second scratch in the vicinity of the first scratch reduced considerably depending on the separation distance. These results are rationalized on the basis of material properties and inherent flaw size. Intergranular fracture and grain dislodgement were found to be the dominant modes of lateral crack propagation.