Here - the ESAFORM 2008 Conference - INSA de Lyon

Performance enhancements of die casting tools trough PVDnanocoatingsM. Rosso 1 , D. Ugues 1 , E. Torres 1 , M. Perucca 2 , P. Kapranos 31 Politecnico di Torino – Cso Duca degli Abruzzi, 24, 10129 Turin (Italy)URL: www.polito.it e-mail: mario.rosso@polito.it; daniele.ugues@polito.it;eloy.torres@polito.it2 Clean NT Lab, Environment Park - Via Livorno, 58/60, 10144 Turin (Italy)URL: http://www.cleanntlab.com/e-mail: massimo.perucca@envipark.com3 The University of Sheffield - Mappin Street, Sheffield, S1 3JD, United KingdomURL: www.shef.ac.uk/materialse-mail: p.kapranos@shef.ac.ukABSTRACT: Wear and failure of die casting dies involve a complex interaction between variousmechanisms. The most important wear and failure modes are summarized as follows: (i) the so-calledwashout damages on working die surfaces are attributed to erosion, corrosion and soldering; (ii) thermalfatigue is the most important failure mode in die casting. The sector of surface thin PVD coatings isconstantly enhancing in order to meet the increasing demand for improved performances of tooling.Advanced PVD coatings are designed to withstand severe mechanical and thermal stress conditions. ACrAlSiN nanostructured coating system was deposited on the base material, modulating the chemicalcomposition so as to increase either the chromium or the aluminium-silicon content. Then, another set ofspecimens was subjected to a cyclic immersion program in a molten aluminium bath. The washout signs weredetected and monitored in function of the increasing number of cycles.Key words: PVD ceramic coatings, aluminium die casting, washout, soldering, modulated PVD composition1 INTRODUCTIONThe process of aluminium die casting presents acomplex phenomenon of degradation, whereerosion, soldering, corrosion, thermal fatigueusually occur jointly. All of these phenomena aremajor sources of limitation to the die castingsservice life. The application of hard PVD coatingsmay result efficient against these degradationmechanisms when applied on particular parts of thedie: e.g. the inlet and the pins.The development of physical vapour deposition(PVD) has provided engineers and systemsdesigners with the ability to tailor the surfaceproperties of a range of mechanical devices to suit agrowing range of applications. Advanced PVDcoatings are designed to withstand severemechanical and thermal stress conditions.Generally, the main requirements expected byadvanced coatings are high hardness andcompression strength, high wear resistance, highmechanical and thermal fatigue resistance and lowfriction coefficient. These parameters may beattained by properly functionalising tools surfaceswith innovative targeted thin films.Furthermore, the adhesion strength at the interfacebetween coating and substrate results of majorimportance to guarantee a long endurance of the toollifetime and surface properties. In the recent years,single layer, multilayer and gradient microstructureshave been developed and now, withtesting of different coating chemistry andstoichiometry, representing the cutting edgesolutions in coating technology.The present paper reports the results of a research onthe effect of PVD films applied on a heat treated hotwork tool steel substrate. The aim of this study wasto determine the behaviour exhibited by eachcoatings in relation with the modulated chemicalcomposition. To this purpose a set of coatedspecimens with chemical composition variationsbased on the CrAlSiN system were produced