EFFECT OF GRAIN-SIZE ON SCRATCH INTERACTIONS AND MATERIAL REMOVAL IN ALUMINA

Dramatic effects of scratch interactions on material removal are obser ved in alumina. A series of parallel scratches are made in aluminas wi th different grain sizes to investigate the influence of scratch inter actions on the material removal process in abrasive machining. The sep aration distance between the two scratches and the normal load are var ied and subsurface microfracture and damage modes are examined to asse ss the mechanisms of material removal. A Very small amount of material is removed when the separation distance between the two parallel scra tches is large or when the two scratches completely ovrlap. However, a t intermediate distances the volume of material removed increases dram atically as a result of the interactions between the two scratches. Th e maximum amount of material removed and the corresponding distance be tween the two scratches are found to depend strongly on the grain size and the load. Observations of surface and subsurface damage reveal th at grain dislodgement is the predominant mechanism of material removal , irrespective of the grain size. The relation between grain size, scr atch interactions, and the material removal process in grinding and ab rasive machining of ceramics is discussed in terms of the short-crack toughness of ceramics.