Micro Structure And Performance Of AlCrSi(Y)N Coatings Deposited By Pulsed Arc Ion Plating

Al-containing transition metal nitrides?e.g.,AlCrN,AlTiN?obtain high hardness and excellent wear resistance and thus are widely used as protective coatings on cutting tools to improve their service life and performance.During oxidation,the AlCrN coating can form a dense and continuous oxide scale,which effectively retards the further oxidation of nitride,and therefore,exhibits excellent oxidation resistance.However,due to the thermal instability of the Cr-N bond and the nature of the supersaturated metastable solid solution,AlCrN will undergo the phase decomposition at elevated temperature,resulting in a sharp drop in mechanical properties.With the development of advanced cutting technology?high-speed and dry machining?and the popularization of difficult-to-machine materials?stainless steel,titanium alloy,etc.?,it is imperative to improve the high-temperature performance of AlCrN coatings to adapt to increasingly harsh requirements for use.In this work,The methods of improving the mechanical properties,wear resistance,high temperature red hardness and oxidation resistance of AlCrN coatings were studied from the point of view of the composition and structure design of tool coatings.Firstly,the alloying elements Y and Si were introduced to the AlCrN coatings,respectively,and investigated with respect to their structure and properties.Second,based on the alloying method,the nano-multilayer coating is further deposited and studies concerning mechanical and high-temperature properties with combining AlCrN sublayers.Finally,the cutting performances of different AlCrN-based coating tools were investigated for difficult-to-machine materials.The main research results obtained are as follows:1)Al_0.70Cr_0.30N and Al_0.70Cr_0.28Y_0.02N coatings were prepared by pulsed arc ion plating technique,and the coating structure,mechanical properties,thermal stability,oxidation resistance and friction and wear properties were compared.Both AlCrN and AlCrYN have single-phase face-centered cubic structures.After annealing at 1100°C,the AlCrYN coating still maintained a high hardness?30.22 GPa?and elastic modulus?392.8 GPa?,while the hardness and elastic modulus of the AlCrN coating decreased rapidly to 20.1 GPa and 302 GPa.After oxidation at 1100°C for 2 hours,the oxide thickness of the two coatings was only 0.52?m?AlCrN?and 0.47?m?AlCrYN?thick.The wear rate of AlCrYN coating at normal temperature and 600°C is lower than that of AlCrN coating,mainly because the addition of Y is beneficial to the preferential formation of Cr₂O₃ and CrO₂,which reduces the friction and wear of the corresponding oxides,and is beneficial to improve the coating of AlCrYN.The wear resistance of the layer.2)To explore the effect of Si addition and arc discharge mode?DC and pulse?,Al_0.68Cr_0.27Si_0.10N coatings were prepared at different duty ratios.The results show that the arc discharge mode and duty cycle have no significant effect on the phase structure and chemical composition of the coating,but the pulse arc mode can effectively improve the surface quality of the coating.With the decrease of the duty cycle,the hardness of the coatings increases gradually,with the best surface roughness and the highest hardness at1%,which are 47 nm and 31.45 GPa,respectively.Due to the addition of Si,the AlCrSiN coatings show better thermal stability and oxidation resistance than the AlCrN coatings,and can still maintain a high hardness of more than 30 GPa after vacuum annealing at950°C for two hours.Also,the oxidation resistance temperatures of AlCrSiN coatings are all over 1000°C,and the oxidation resistance of coatings prepared by the pulsed arc is slightly higher than that of DC arc.3)Based on the above research,the multilayer structure was designed.The modulation periods of AlCrN/AlCrSiN and AlCrN/AlCrYN nano-multilayer coatings were 21 and 16 nm,respectively.Among them,AlCrN/AlCrYN coating has a higher hardness?36.46 GPa?,elastic modulus?517.3 GPa?,bonding force?78 N?and wear resistance than AlCrN/AlCrSiN coating,while its oxidation resistance is slightly worse than that of AlCrN/AlCrSiN coating.The nano-multilayer structure is helpful to improve the hardness,wear resistance and oxidation resistance of the coatings.The comprehensive properties of the coatings are superior to those of the single-layer coatings.The service life of stainless steel?SUS304?and titanium alloy?Ti-6Al-4V?in coated tool turning is AlCrN<AlCrSiN<AlCrYN<AlCrN/AlCrSiN<AlCrN/AlCrYN,respectively.The main forms of turning stainless steel?SUS304?are flank wear,crescent depression wear,groove wear,plastic deformation and adhesive oxidation wear.The main forms of turning titanium alloy?Ti-6Al-4V?are adhesive wear,abrasive wear,oxidation wear,and plastic deformation wear.