Film thickness effect on mechanical properties and milling performance of nano-structured multilayer PVD coated tools

Abstract

Abstract The paper aims at clarifying whether thick HPPMS (High Power Pulsed Magnetron Sputtering) PVD coatings can be used more effectively in cutting processes compared to thin ones. In this context, nano-structured multilayer HPPMS PVD coatings with diverse thickness were deposited on cemented carbide inserts of the same specifications. The deposition of multilayer PVD coatings instead of mono-layer ones on cemented carbide tools contributes to a significant improvement of the coated tool life due to their capability to prevent the crack propagation. The coating's mechanical properties and their gradation versus the film thickness were determined by analytical results' evaluation of nanoindentations on annealed coated specimens. The films' brittleness was assessed by nano-impact tests. The strain rate-dependent fatigue endurance of the applied coatings was determined by means of impact tests with modulated force signals, resembling the developed ones during milling. The coated inserts were used in milling hardened steel. A Finite Elements Method (FEM) simulation of the contact between the coated tool and the workpiece provided information for elucidating the effect of the film thickness on the tool wear evolution. These investigations revealed that via increasing the film thickness the tool life is prolonged almost proportionally with the coating thickness augmentation, thus compensating for their higher cost compared to thin coatings.