The coating of special tools allows to add a micrometric layer of hard elements (e.g., titanium nitride, carbonitrides of titanium and alumina, DLC, carbon, diamond) in order to lend greater surface hardness to the cutting wedge and an improvement in the state of the surfaces to facilitate the sliding of the chip.
Coating is most effective when the tool substrate is harder and uniform. Elements and methods of contribution depend on the materials which have to be processed and on the tool material.