Tribological adaptability of TiAlCrN PVD coatings under high performance dry machining conditions

The application of ternary nitride (Ti,Cr,Al)N coatings with high aluminum content deposited by a new plasma enhanced cathode method results in a significant cutting tool life improvement. To investigate this improvement the tool life of end milling cutting tools was studied under severe conditions associated with the high speed dry machining of H13 steel (hardness HRC 50). Investigations of the surface structure characteristics for the different compositions of TiAlCrN as well as TiAlN coatings using SEM, EDS, AES, and XPS were performed. The coefficient of friction and oxidation stability of the coatings were also measured at elevated temperatures. It was shown that the major cause of the improved cutting tool life is the adaptability of the (Ti0.10Cr0.20Al0.70)N coating under conditions experienced during high performance machining. The tribological adaptability manifests itself through the formation of complex alumina/chromia-like tribo-films on the surface of the cutting tool. This tribo-film formation serves to protect the surface of the tool and improve its lubricity during cutting. Due to the presence of these beneficial films the tendency of the workpiece material to adhere to the tool within the cutting zone is also reduced. The shape and microstructure of the chips formed during end milling were also analyzed. Both of these characteristics indicate significantly improved lubrication properties at the cutting tool/workpiece interface when the TiAlCrN coating is applied.