Material removal mechanism and deformation characteristics of AlN ceramics under nanoscratching

Abstract To investigate the fundamental mechanism of the deformation and fracture behavior of aluminum nitride (AlN) ceramics in ultra-precision grinding, single and double scratches of AlN ceramics were carried out using a Berkovich indenter. Depth-displacement curve and surface morphology of the single varied force scratch revealed that the brittle-ductile transition occurs during scratching. In the brittle deformation stage, the stress below workpiece surface plays an key role in the change of scratch direction, and grains spall due to crack propagation. Depth-displacement curves and surface morphology of the double scratches revealed that the second and first scratches merge into one scratch in the case of the double scratches with distance of 0.5 μm and 1 μm, leading to the increase in the second scratch depth. A double-scratching-induced stress field model under constant force was established using the Boussinesq field, the Cerruti field, and the sliding bubble field to investigate interaction principle of double scratches and the material removal mechanism of AlN ceramics. Results indicated that the interaction of double scratches leads to the increase in the maximum principal stress of lateral cracks; the maximum principal stress reaches the extreme value after the indenter is unloaded; and the interaction of lateral cracks between double scratches leads to in overall removal of workpiece material and the slip of the second scratch.