Laser coatings to improve wear resistance of mould steel

Laser surface treatments can be used as a powerful tool to repair moulds which have experienced severe damage during their service lifetime. The present paper studies the application of cladding techniques to repair moulds such as those used in the plastics industry. By means of a continuous wave diode laser operating at 600 W output power, a tool steel—annealed AISI A2—has been coated with two alloys with different protective properties: a high-speed steel with a high molybdenum content (AISI M2) and excellent mechanical properties; and a martensitic stainless steel (AISI 431) which combines good wear and corrosion resistance. After the treatment, the clad surfaces were characterised by means of optic and scanning electron microscopy. The layers showed a uniform composition across the track, similar to the initial powder composition, without damage or cracks. The mechanical properties were evaluated by hardness measurements and wear tests (ball-on-disk) at room temperature and without lubrication, in accordance with the ASTM G99-95a standard. The tribological couple was comprised by an alumina ball sliding against the clad layers. The wear rate varied with the different ball and disk combinations, and a considerable improvement in wear resistance was observed with the AISI M2 laser coatings compared with the substrate.