INVESTIGATION OF NANO-STRUCTURED PVD COATINGS FOR DRY HIGH-SPEED MACHINING

Abstract

The objective of this paper is to investigate the performance of different categories of hard PVD coatings in terms of friction and tool wear under dry high-speed machining (HSM) conditions. In this study five different categories of commercially available coatings (nano-composite AlTiN/Si₃N₄, nano-crystalline Al₆₇Ti₃₃N and mono-layered Ti₁₀Al₇₀Cr₂₀N) and experimental nano-multilayered coatings (Ti₂₅Al₆₅Cr₁₀N/BCN and Ti₂₅Al₆₅Cr₁₀N/WN) were studied by machining hardened steel AISI H13 (HRC 50). The coefficients of friction against steel versus temperature were measured. Tool wear and cutting forces were measured in-situ under dry high speed machining conditions. The morphology of the worn tools and the chips collected during cutting were studied using an SEM (Scanning Electron Microscopy) and the EDX (Energy Dispersive X-ray analysis). The cutting temperatures were estimated based on the color of the chips generated during cutting. The comparison among these categories of coatings was conducted based on tool wear, coefficient of friction, cutting forces and chip formation. From this study, it was revealed that the solid self-lubricating layers, automatically formed in the cutting zone under elevated temperatures, play a key role in leading to a significant improvement of tool performance under dry high-speed machining.