Effect of Al content on adhesion strength of TiAlN coatings

Ti0.5Al0.5N, Ti0.45Al0.55N and Ti0.4Al0.6N coatings were deposited on WC-6Co cemented carbide substrate by cathodic arc evaporation, and the adhesion strength of TiAlN coatings was measured by a scratch tester equipped with acoustic emission monitoring. The effect of Al content on the adhesion strength of TiAlN coatings was investigated, as well as the failure modes. The tested results show that the adhesion strength of Ti1-xAlxN (x=0.5-0.6) decreases with the increasing Al content in the coating. The adhesion strength is affected by the residual stress of coatings and the hardness difference between coating and substrate. Ti0.5Al0.5N coating exhibits the highest adhesion strength due to lower residual stress and the minimum hardness difference. The optical microscope observation of scratch channels indicates that the failure mode of Ti0.5Al0.5N and Ti0.45Al0.55N coatings is wedging spallation, whereas the failure mode of Ti0.4Al0.6N is buckling spallation. The increase of Al content decreases the adhesion strength, but helps to improve the toughness of coatings. Especially the toughness of Ti0.4Al0.6N coating increases obviously owing to a small amount of soft h-AlN phase. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.