Effect of nitriding pretreatment on adhesion and tribological properties of AlCrN coating

• A nitriding pretreatment increases the adhesion of AlCrN coating on 4140 steel. • The adhesive failure mode of AlCrN is changed to cohesive by the nitrides layer. • The COF of AlCrN is reduced to 50% due to the nitriding pretreatment. • The specific wear rate of AlCrN is greatly reduced by the nitriding pretreatment. In this work, a gas nitriding pretreatment (iron nitrides layer) formed on the surface of 4140 steel is proposed to improve the adhesion and wear resistance of the AlCrN coatings deposited by arc cathodic PVD. AlCrN, Fe x N and AlCrN/Fe x N (duplex) systems were formed with total thicknesses of 3, 10 and 13 µm, respectively. Using spherical instrumented indentation, hardness more than 22 GPa were determined for the AlCrN-based coatings, meanwhile 10 GPa for the iron nitrides. The adhesion of the coatings were evaluated by progressive load scratch tests (PLST) where the duplex coating reduced the CoF and changed the failure mode from adhesive to cohesive for the AlCrN coating. The AlCrN/Fe x N coating exhibited the lowest specific wear rate and the severity of damage was reduced in multipass scratch wear tests (MPST). The duplex system presented the best adhesion and wear resistance.