The SEM images show that, by using AFM, layers of material are removed in a gentle manner with a mainly ductile material removal mechanism. As a result of the machining process, typical washed-out surface textures are created, while nondirectional traces, grain boundaries, and edges of microcracks have been smoothed out. The layer-by-layer removal of the surface leads to the uncovering of existing imperfections beneath the surface, while grains within the workpiece are broken off only when their grain boundaries are close to failure.
Figure 6.55 shows a comparison of different ceramics and their improvement in surface roughness due to AFM. The most significant improvements can be achieved within the first few minutes of the process. It can also be observed that the attainable surface quality depends on the size of the abrasive grains used as well as the fracture toughness of the ceramic.