CrN/AlN and CrN/AlN/Al2O3 coatings deposited by pulsed cathodic arc for aluminum die casting applications

• High compressive stresses were induced into the substrate by means of a specific pretreatment process.
• Aluminum die casting application-related rotating immersion tests were conducted.
• Deposition of amorphous Al2O3 by means of modified pulsed cathodic arc evaporation
• CrN/AlN/Al2O3 exhibits no damages after application-related immersion tests in 333.1.

In aluminum die casting applications corrosion and wear resistance have significant influence on tool life and product quality. Multilayer coatings based on transition metal nitrides such as CrN and AlN deposited via physical vapor deposition (PVD) have shown great advantage as protective coatings on tools and components subject to high loads in tribological conditions. Al2O3 coatings offer high potential to be used as protective coatings on die casting applications due to their high hardness, high chemical inertness and thermal stability. However, the deposition of Al2O3 onto steel substrate demands the use of a bond coat such as CrN/AlN in order to improve its adhesion on the substrate. The present work deals with the investigation of a specific pretreatment process of the substrate material AISI H11 hot work steel, consisting of quenching and tempering, plasma nitriding and pressure blasting, as well as the investigation of CrN/AlN and CrN/AlN/Al2O3 coatings deposited using pulsed cathodic arc evaporation (CAE). The chemical composition, morphology and structure were analyzed by means of energy-dispersive X-ray spectroscopy (EDS), electron probe micro-analysis (EPMA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. Mechanical properties were determined by means of nanoindentation. The coating adhesion was studied using the Rockwell (HRC) indentation method and scratch test. The wear and corrosion resistance of the coated substrates were investigated using a rotating immersion test in the aluminum based alloy A333.1 (EN AC-46000) at T = 680 °C for t = 2 h and t = 6 h and EDS linescans. The material is an aluminum based alloy with a high silicon content, which is used for aluminum die casting applications such as engine blocks or die casting core inserts. The results revealed that a high adhesion of the CrN/AlN and CrN/AlN/Al2O3 coatings to the steel substrate was achieved. The CrN/AlN/Al2O3 showed a reduced wettability affinity to the aluminum melt and a high wear resistance. Furthermore, the Al2O3 top layer prevented corrosion from liquid metal between the aluminum based melt and the hot work steel substrate. Based on these results the CrN/AlN/Al2O3 coating is a promising candidate to be applied on aluminum die casting tools.