Analysis of CrN/AlN/Al2O3 and two industrially used coatings deposited on die casting cores after application in an aluminum die casting machine

In aluminum die casting damage mechanisms, such as abrasive and adhesive wear, corrosion due to metallic melt as well as heat-shock cracks by thermo-cyclical load, have significant influence on tool life and product quality. Multilayer coatings like CrN/AlN/Al2O3 based on transition metal nitrides such as CrN and AlN and oxide toplayers such as Al2O3 deposited via physical vapor deposition (PVD), offer high potential to be used as protective coatings due to their high hardness and chemical inertness. The present work deals with the investigation of a CrN/AlN/Al2O3 coating deposited by using pulsed cathodic arc evaporation and two industrially used hard coatings on AISI H11 (1.2343) hot work steel. In a first step the coatings were investigated after application related tribological rotating immersion tests. In a second step a damage analysis of coated die casting cores after application in an industrial aluminum die casting machine was carried out. In order to investigate the temperature stability of the Al2O3 toplayer of CrN/AlN/Al2O3, the coating was annealed at T = 600 °C for t = 2 h and analyzed by means of high-resolution transmission electron microscopy (HRTEM) and selected area diffraction (SAD). For the purpose of analyzing the corrosion resistance of the coatings against aluminum die casting melt A333.1 (EN AC-46000), rotating immersion tests at T = 680 °C were conducted. The tested samples were analyzed by means of SEM and electron probe micro analysis (EPMA). Further, the coated die casting cores were applied in an industrial aluminum die casting machine. After 5884 shots the coated cores were analyzed by means of SEM and energy-dispersive X-ray spectroscopy (EDS). Analyses of the thermal stability by means of TEM showed that the Al2O3 toplayer of the CrN/AlN/Al2O3 coating was deposited in an amorphous state and transformed into partially crystalline γ-Al2O3. Nevertheless, the results of the core analyses after 5884 die casting shots indicate a good performance of CrN/AlN/Al2O3, also in comparison to industrially used coatings.