Abstract
Thin hard coatings are widely known as key elements in many industrial fields, from equipment for metal machining to dental implants and orthopedic prosthesis. When it comes to machining and cutting tools, thin hard coatings are crucial for decreasing the coefficient of friction (COF) and for protecting tools against oxidation. The aim of this work was to evaluate the tribological performance of two commercially available thin hard coatings deposited by physical vapor deposition (PVD) on a high speed tool steel (S600) under extreme working conditions. For this purpose, pin-on-disc wear tests were carried out either at room temperature (293 K) or at high temperature (873 K) against alumina (Al2O3) balls. Two thin hard nitrogen-rich coatings were considered: a multilayer AlTiCrN and a superlattice (nanolayered) CrN/NbN. The surface and microstructure characterization were performed by optical profilometry, field-emission gun scanning electron microscopy (FEGSEM), and energy dispersive spectroscopy (EDS).
Highlights
The evolution of industrial processes makes them faster and more demanding from a material resistance point of view
Concerning the perspectives of productivity and cost-effectiveness, there are different critical factors that certainly deserve to be considered, such as: (i) the need to increase the productivity by raising the cutting speed, (ii) the need to extend the lifetime of tools, and (iii) the need to lower the cost of tooling, which is typically in the range of 2–5% of the total manufacturing costs [4]
Given the results reported on the thermal stability of these two coatings published by some of the authors in the present study [64], where the superlattice coating showed degradation of its mechanical properties at around 873 K, this temperature was chosen as the highest to be set in order to evaluate the tribological performance of the two commercially available coatings
Summary
The evolution of industrial processes makes them faster and more demanding from a material resistance point of view. This draws attention to the technological and environmental issues that still affect the crucial production steps such as cutting and machining. Thin hard coatings have been successfully employed in a variety of applications, from tools, dies, and molds to aerospace and automotive fields [4,7,8,9,10]. The deposition of hard and tough coatings helps prevent brittle failure when tools are subjected to external stresses [11] and, Metals 2019, 9, 332; doi:10.3390/met9030332 www.mdpi.com/journal/metals
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