Effect Of Alloying On Microstructure And Properties Of Magnetron Sputtering Deposited CrAlN Nano-multilayer Coatings

In recent years,with an increasingly serious problem of environmental pollution,the use of cutting fluid in machining process has been unable to meet the needs of sustainable development.Dry cutting or a small amount of cooling and lubrication technology has become the development direction of green manufacturing.Because of the lack of effective auxiliary cooling lubrication in the dry cutting process,the requests on hard coatings deposited on cutting tools are more and more restrict.The widely used TiN and CrN series coatings are difficult to meet the requirements in dry cutting conditions.Therefore,it is essential to research and develop the coatings for dry cutting to improve the tool life and realize the green manufacture.CrAlN coatings have been widely used for cutting tools due to their high hardness,especially excellent thermal stability and oxidation resistance.However,the rapid development in dry cutting applications demands further improvement in toughness and wear properties of CrAlN coatings.In this paper,a series of researches about how to further improve the wear resistance,high temperature oxidation resistance and toughness of CrAlN thin films were carried out based on the design idea of nano multilayer structure and multi alloying.CrAlN,CrAlMoN,CrAlYN and CrAlNiN nano-multilayer coatings were deposited on M2 tool steel and silicon wafers substrates by closed-field unbalanced magnetron sputtering ion plating?CFUMSIP?technique.The chemical composition,microstructure and properties of coatings were studied by EDS,SEM,XRD,XPS,nano-indentation and pin-on-disk tribometer,resistance furnace,electrochemical station,respectively.The main conclusions in this work are summarized as follows:?1?Mo existed as Mo₂N forms in the modulation of CrAlMoN nano-multilayer coating.Mo alloying did not change the fcc structure of CrAlN coating.In room temperature,Nano indentation result revealed a promoted hardness and elastic modulus of the CrAlMoN coatings with enhanced Mo content from 0 to 19.47 at.%.The average friction coefficient and wear rate were observed to decrease with the increase of Mo content due to the formation of self-lubricating MoO₃.?2?In high temperature condition,the volatilization reaction rate of MoO₃ increased,breaking the dense and protective oxide layer consisting of Cr₂O₃ and Al₂O₃.The porous became clearly observable on the surface of the coating,which provided fast diffusion paths for oxygen and cations,and thus promoted the growth rates of oxide scales.The mechanical properties and adhesive strength of CrAlMoN coating decreased drastically.?3?Rare earth Y could increase the sputtering yield of AlY target and promote the growth of the coating.The hardness and high temperature oxidation resistance of CrAlN nano multilayer coatings could be improved by doping a small amount of rare earth Y into the AlN layer.The CrAlYN?Y content 1.13at%?coating could maintain high mechanical properties after 1000?oxidation at 2h.Y alloying beyond 1.13%would deteriorate the oxidation resistance of the CrAlYN coating due to the formation of Y-Al oxide within the oxide scales.?4?Ni existed as elemental and nitrides mix phase in the modulation of CrAlMoN nano-multilayer coating.With the increase of Ni content,the more elemental Ni exsited in modulation layer,the alternating modulation layer which consisted of Ni soft phase and CrN,AlN hard phase had obvious toughening effect.The conclusion of this study can provide theoretical basis for the alloying modification of CrN,TiN and ZrN series coatings.Meanwihile CrAlMoN,CrAlYN and CrAlNiN nano-multilayer coatings are expected to be used in dry cutting service environment.