CrN/AlN nanolaminates: Architecture, residual stresses, and cracking behavior

Abstract

Hard coatings deposited by physical vapor deposition are state of the art for wear and corrosion protection of manufacturing tools. Nanolaminate coatings such as CrN/AlN consist of hundreds of CrN and AlN alternating layers and stand out among nitride hard coatings by their mechanical properties, i.e., high hardness combined with high toughness. Until now, the characteristics of CrN/AlN nanolaminates deposited in large scale industrial coating units using simultaneous direct current magnetron sputtering (dcMS) and high power pulsed magnetron sputtering (HPPMS) power supplies in hybrid dcMS/HPPMS processes have hardly been investigated. In this paper, two CrN/AlN nanolaminates are compared, which were deposited on tool steel X42Cr13 in a hybrid process using an industrial coating unit with six cathodes. Analyses of the mechanical properties were performed by nanoindentation in the low and high range load regimes as well as under very high quasistatic loads using the Rockwell penetration test. The residual stresses of the coatings were investigated using a dedicated ring-core milling method based on a focused ion beam. One of the two coatings was found to have a very high compound adhesion to the steel substrate rated with the best adhesion category HF1, despite residual compressive stresses of σ ≈ −5.4 GPa. This coating system also showed significantly higher hardness, compressive strength, and crack resistance compared with the other coating for which residual compressive stresses of only σ ≈ −0.9 GPa were measured. The relationship between the adjustable residual stresses in nanolaminate hard coatings and the strength requirements in the application can be used for the targeted design of coatings for manufacturing tools. The residual stresses and the influence of the rotation and bias voltage on those were analyzed for the first time for nanolaminates using the focus ion beam ring-core milling method.