Tribomechanical Behaviour of TiAlN and CrAlN Coatings Deposited onto AISI H11 with Different Pre-Treatments

Diego Grisales,Timo Butzke,Dominic Stangier,Wolfgang Tillmann

doi:10.3390/coatings9080519

Abstract

In the metalworking industry, different processes and applications require the utilisation of custom designed tools. The selection of the appropriated substrate material and its pre-treatment as well as the protective coating are of great importance in the performance and life time of forming tools, dies, punches and coated parts in general. TiAlN and CrAlN coatings have been deposited onto the hot work tool steel AISI H11 by means of Direct Current Magnetron Sputtering. Prior to the deposition, the steel substrate was modified by the implementation of three different pre-treatments: nitriding of the annealed substrate [Nitr.], heat treatment of the steel (quenching and double tempering) [HT] and nitridation subsequent to a heat treatment of the substrate [HT + Nitr.]. The purpose of this research is to obtain valuable information on the microstructural properties and tribomechanical behaviour of two of the most promising ternary transition metal nitride coatings, TiAlN and CrAlN, when deposited on the AISI H11 steel with different initial properties. The different pre-treatments performed to the steel prior to the deposition favour the tailoring during the design and construction of tools for specific applications. The microstructure, the adhesion and the wear resistance of TiAlN coatings were highly influenced by the substrate preparation. Contrarily, CrAlN results were more independent of the substrate preparation and no high influences were found. For instance, the adhesion of the TiAlN coating varied from 17 to 43 N for the coating deposited onto the HT + Nitr. substrate and the HT substrate respectively, while the lowest and highest adhesion of the CrAlN coating varied between 42 and 53 N for the HT and the HT + Nitr. respectively. Likewise, the wear coefficient of the CrAlN were ten times smaller than those found for the TiAlN coatings, presumably due to the presence of hex-AlN phases and the small differences on the Young´s Modulus of the substrate and the CrAlN coatings.

Highlights

Surface modifications on forming tools and metallic components exposed to tribological environments are widely extended practices in modern manufacturing to enhance their tribological performance
The severe sputtering of the surface caused by the nitrogen ions and the applied voltage increases the roughness of the surface, an effect investigated by other authors [41]
CrAlN/substrate systems have presented significantly lower wear coefficients when compared with TiAlN/substrate compounds and to the substrates

Summary

Introduction

Surface modifications on forming tools and metallic components exposed to tribological environments are widely extended practices in modern manufacturing to enhance their tribological performance. In order to increase the service life of tools manufactured using AISI H11, heat treatment and nitriding processes have been the most traditional approaches to reduce wear on the components [2,3,4,5]. With the introduction and industrial massification of protective nitride coatings, an additional overlay process has been proposed for the wear protection of sliding components. To this end, TiN and CrN are the most commonly employed coating materials due to their relatively high hardness, wear and corrosion resistance. With the inclusion of aluminium into the Coatings 2019, 9, 519; doi:10.3390/coatings9080519 www.mdpi.com/journal/coatings

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