Effect of Grain Size on Scratch Interactions and Material Removal in Alumina

Dramatic effects of scratch interactions on material removal are observed in alumina. A series of parallel scratches are made in aluminas with different grain sizes to investigate the influence of scratch interactions on the material removal process in abrasive machining. The separation distance between the two scratches and the normal load are varied and subsurface microfracture and damage modes are examined to assess the mechanisms of material removal. A very small amount of material is removed when the separation distance between the two parallel scratches is large or when the two scratches completely overlap. However, at intermediate distances the volume of material removed increases dramatically as a result of the interactions between the two scratches. The maximum amount of material removed and the corresponding distance between the two scratches are found to depend strongly on the grain size and the load. Observations of surface and subsurface damage reveal that grain dislodgement is the predominant mechanism of material removal, irrespective of the grain size. The relation between grain size, scratch interactions, and the material removal process in grinding and abrasive machining of ceramics is discussed in terms of the short-crack toughness of ceramics.