Corrosion-wear behaviour of PVD Cr/CrN multilayer coatings for gear applications

Abstract

At present, one of the most important problems in automobile engines and transmission components is due to tribological processes (friction and wear) that in many cases come accompanied by corrosion processes due to the environmental conditions to which these materials are exposed during their lifetime. Both mechanisms can be minimized by means of the development and the application of adequate coatings that combine low friction with a high corrosion and wear resistance. The new tendencies in industrial PVD coatings to improve their properties are focused in the development of new multilayer and nanostructured coatings. These structures allow in a relatively simple way enhancing their tribological properties and the corrosion resistance that can not be reached by means of the traditional monolayer coatings. The background of this type of coatings consists of the stacking up of several layers with good individual tribological and mechanical properties, but every individual layer has a thickness that can be from hundreds of nanometres down to only 5-10 nm. The properties of these nanostructured coatings depend strongly on the thickness modulation of every individual layer. Concerning PVD coatings, the chrome nitride coatings have demonstrated to possess excellent wear resistance properties. In this work, multilayer Cr/CrN coatings with different individual layer thickness have been deposited on substrates of steel F1272 and silicon. The deposition has been carried out by means of the cathodic arc method alternating an atmosphere of pure Ar with a reactive mixture of N2/Ar. The multilayers obtained have been analyzed by means of Glow Discharge Optical Emission Spectroscopy (GD-OES) and in some cases by means of FE-SEM obtaining bilayer (Cr/CrN) periods of the order of 220 and 45 nm. The coating characterization has been complemented with hardness and composition measurements as well as by the performance of several wear and corrosion-wear tests. © 2008 Elsevier Ltd. All rights reserved.