Preparation And Property Research Of AlCrN Hard Coatings Containing Rare-earth Elements

AlCrN coatings are extensively used in cutting tools and forming molds owing to good mechanical properties and wear resistance.However,the rapid development of modern cutting technologies and the widespread application of difficult-to-machine materials have placed higher requirements on tool coatings,involving not only high hardness and wear resistance but also smooth surface and low friction.The thesis firstly aims at improving the surface quality of AlCrN coatings by optimizing the cathode magnetic field configuration and deposition parameters.Then,the influence of rare earth elements,Y and Sc,on mechanical,anti-oxidative and tribological properties of AlCrN coatings was investigated.The main research results are summarized as follows:1.The intensity of the cathode magnetic field in the horizontal and vertical target directions will significantly affect the erosion of the target during deposition.Increasing the current of the electromagnetic coil will cause the arc spot to concentrate on the edge of the target,and the enhanced magnetic field will make the arc spot move faster and thus improve the surface quality of coatings.As the horizontal component of the magnetic field increases,the hardness of the AlCrN coating increases,the coefficient of friction against the stainless steel ball decreases slightly at room temperature,and the wear resistance increases.During high-temperature oxidation,the AlCrN coating prepared after the magnetic field is strengthened is more dense with small size and number of macro-particle defects,so its oxidation resistance is better.2.The increase of the substrate bias voltage can further improve the surface quality of the AlCrN and AlCrYN coatings,and can inhibit the formation of Al N hexagonal phases to improve the mechanical properties.The Y-addition will introduce more macro-particles defects and reduce the solid solubility of Al N in Cr N.In addition,alloying with Y significantly improves the mechanical properties of the Al₅₀Cr₄₈Y₂N coating,but due to the precipitation of wurtzite Al N,it has little effect on the hardness of the Al₇₀Cr₂₈Y₂N coating.At high temperatures,the oxidation rate of the Y-containing coating is faster.3.Al_0.739Cr_0.261N and Al_0.736Cr_0.238Sc_0.026N coatings were deposited by cathodic arc evaporation and comparatively studied concerning structure,mechanical properties and oxidation resistance.The addition of the rare earth element Sc reduces the metastable solid solubility of Al and promotes the formation of the hexagonal phase Al N.However,even with the presence of hexagonal Al N,the solid solution of large atoms Sc in AlCrN significantly increases the hardness.The preferential oxidation of Sc at high temperature breaks the formation of dense(Al,Cr)₂O₃ oxide layer,thereby reducing the oxidation resistance of AlCrN coating.