On the effect of grain structure in micro-cutting of polycrystalline aluminate magnesium spinel (PAMS) crystals

•Ductile–brittle transition of spinel occurs with a cutting depth from 80 to 163 nm.•Crack distribution owes to material anisotropy of randomly oriented grains.•Crack-free surface can be achieved with a cutting depth in tens of nanometers.•Ploughing effect dominates the cutting process with a cutting depth below 100 nm.•Subsurface damage and fractures are evoked ahead of material removal process.