Comparison of (Ti,Al)N and (Ti,Al)N/γ-Al2O3 coatings regarding tribological behavior and machining performance

Over the last decade the amount of application of difficult-to-machine materials has increased considerably due to the demand on new innovative products. (Ti,Al)N coatings deposited using PVD technology have already proven their capabilities by improving tool life over the years in the machining industry. γ-Al2O3 coatings by PVD technology are relatively new but provide good features. However, the deposition of γ-Al2O3 onto cemented carbide demands the use of a bond coat such as (Ti,Al)N in order to improve its adhesion on the substrate. In the present work (Ti,Al)N and (Ti,Al)N/γ-Al2O3 coatings were deposited on cemented carbides by means of Magnetron Sputter Ion Plating (MSIP) in order to compare their tribological behaviors and machining performance in face milling operation against austenitic steel 1.4571 (X6CrNiMoTi17-12-2) under dry condition. The analysis of deposited coatings was carried out with thin film characterization methods. The coating morphology and thickness were determined using Scanning Electron Microscopy (SEM). Glow Discharge Optical Emission Spectroscopy (GDOES) was used to determine the chemical composition. Mechanical properties were analyzed by using the nanoindentation. The further development of (Ti,Al)N applying γ-Al2O3 as top layer leads to a considerable reduction of abrasive and adhesive wear even at elevated temperatures. It could be shown that the (Ti,Al)N/γ-Al2O3 coating offers notable advantages for the application in dry milling operations of austenitic steel.