Study On The Structure And Properties Of Al-Cr-O Hard Coatings Deposited By Cathodic Arc Evaporation

The application of high-speed cutting and dry cutting technologies puts forward higher requirements on the overall performance of the tool coating.In recent years,corundum（Al,Cr）₂O₃ coatings can be synthesized by cathode arc evaporation technology at lower temperatures（<600°C）and in a wide composition range and exhibit good mechanical properties,thermal stability,and chemical inertness,which have attracted much attention.However,（Al,Cr）₂O₃ coatings still face some challenges in industrial application.First of all,the negative effect of"target poisoning"during the preparation of the coatings on the process stability and coating growth,and the second is to achieve effective control of the structure and properties of（Al,Cr）₂O₃ coatings.Therefore,the thesis optimized the cathode magnetic fields and deposition atmosphere to reduce the"target poisoning"with a stable coating process.Then,the energy of the film-forming particles is controlled by substrate bias.Finally,the influence of Cr content on the structure and properties of（Al,Cr）₂O₃ coating were studied.The main research results of this thesis are as follows:1.As compared to the MAG1 magnetic fields generated by a permanent magnet and electromagnetic coils,the MAG2 magnetic fields generated only by electromagnetic coils effectively slows down the degree of"target poisoning",improving the stability of the preparation process and utilization rate of the target,while did not improving the surface quality of（Al0.5Cr0.5）2O3 coatings.The introduction of argon to keep₂:=1:4 can also effectively slow down the degree of"target poisoning",but the higher partial pressure of argon increases the splashing of the large particles,which resulted in increased particle defects.In the atmosphere of pure oxygen within 0.75～3.0 Pa,lower pressure is more conducive to avoiding the aggravation of"target poisoning"and the incorporation of particle defects.2.With the increase of the substrate bias voltage,the macro-particle defects on the surface of the(Al_0.5Cr_0.5)₂O₃ coatings were reduced,and the residual stress and adhesion strength first increase and then decrease.When the substrate bias voltage is-100 V,the coating has the highest adhesion force of 60.5 N.Appropriately increasing of substrate bias voltage increases the ion energy and bombardment effect,can obviously promote the crystallization of the(Al_0.5Cr_0.5)₂O₃ coatings and is conducive to the formation of thermodynamically stableαphase.With a substrate bias of-150 V,(Al_0.5Cr_0.5)₂O₃ coatings have the highest hardness and elastic modulus of 32.4±1.2 GPa and 376.2±16.3 GPa,respectively.The friction coefficient of the coatings decreases with the increase of the substrate bias voltage.When the substrate bias voltage is-200 V,the coating had the smallest coefficient of friction of 0.45.3.There were apparent differences in the erosion of Al-Cr alloy targets with different compositions.The target with Al₅₀Cr₅₀at.%has the most severe"poisoning".The increase of Cr content can promote the crystallization of（Al,Cr）₂O₃ coatings.The high Al-content(Al_0.7Cr_0.3)₂O₃ coating mainly consisted of the amorphous phase,α,andγphase.(Al_0.5Cr_0.5)₂O₃,(Al_0.3Cr_0.72)O₃,and Cr₂O₃ coatings shown a singleαphase structure.(Al_0.5Cr_0.5)₂O₃ coating had the highest hardness and elastic modulus of 32.3±1.6 GPa and374.1±21.6 GPa,respectively.Whereas,the friction coefficient of Cr₂O₃ coating is 0.37,lower than～0.55 of Al-containing （Al,Cr）₂O₃.