Effect of grain size on dynamic scratch response in alumina

The machining and wear of ceramics and ceramic components are influenced by abrasive damage. One parameter that can affect the abrasion process is the grain size of the ceramic material. To investigate this, a single-grit pendulum scratch tester was used to study the dynamic scratch response in three 99.9% aluminas that each had a tight size distribution about mean grain sizes of 2, 15, or 25 μm, respectively. The scratch speeds generated had an order of magnitude of ∼ 1,000 mm/s and the maximum scratch depths were ∼ 45 ∼m. Tangential and normal scratch forces were monitored during each test and interpreted in conjunction with postmortem SEM (scanning electronic microscopy) and profilometry results. It was observed that both plastic deformation and brittle fracture participated in the scratching process and the relative activity of each was dependent on the depth of penetration. At a given depth, the material removal of alumina prevailingly relies on the generation and interaction of oblique radial and lateral cracks. Chip formation is greatly enhanced when the cracks interact and that interaction depends on grain size. Larger grain size gives rise to larger lateral cracks, more severe fracture at the groove bottom, and larger amplitude of scratch force oscillation. Lastly, the instantaneous specific energy (cutting pressure) and scratch hardness of alumina exhibited various sensitivities to the grain size and groove depth.