Subsurface deformation of machined Al2O3 and Al2O3/5vol%SiC nanocomposite

Under machine grinding, material removal in monolithic Al2O3 is by intergranular fracture and grain pull-out. In comparison, under the same grinding conditions, an Al2O3/ 5%SiC nanocomposite undergoes significant surface grooving and intragranular fracture. The subsurface deformation mechanisms were investigated by cross-sectional transmission electron microscopy. For Al2O3, the residual deformation zone was localized very close to the surface in the first layer of grains, with dislocations occurring only within 1.5 mum of the top surface and a high density of basal twins penetrating to a depth of one single grain. Cracks were present along grain boundaries or basal twin interfaces. For Al2O3/SiC nanocomposites, the main residual plastic deformation is observed to be dislocations activated to a depth of about 10 mum (approx. 3-4 grains), with twinning rarely observed. Possible mechanisms by which the SiC particles influence the subsurface deformation and material removal modes are discussed.