Preparation And Corrosion Resistance Of Cr-Al-C Coatings

Corrosion will not only seriously reduce the service life of metal materials,but also cause huge economic losses and environmental pollution.Therefore,how to effectively improve corrosion resistance has become a research hotspot in the industrial application of metal materials.Binary Cr-C coatings are widely used as surface protective coatings due to their high hardness,good corrosion resistance and excellent chemical stability.However,because of its high brittleness,the Cr-C coating is prone to cracks and other defects during the preparation process,which greatly reduces its stability and durability as an anti-corrosion coating.In this work,a ternary CrAlC coating was prepared by adding Al to the binary Cr-C coating based on the magnetic filtered ion plating（FCVA）technology to effectively improve the corrosion resistance of the coating.In addition,in order to optimize the preparation process of ternary CrAlC coatings,the effects of acetylene ventilation,alloy target composition,annealing temperature and film structure on the coating microstructure,mechanical and electrochemical corrosion properties were systematically investigated.The main work and conclusions are as follows:（1）The results of the study on the influence of C₂H₂/Ar flow ratio and Cr Al alloy target composition on the performance of CrAlC coatings show that the surface of the coating prepared by different processes is uniform and compact but with a small number of particles and holes.With the increases of C₂H₂/Ar flow ratio from 1/12 to 1/4,the content of Al₄C₃ and Cr₂₃C₆ increased,while the content of Al₃Cr₇ decreased.Due to the increase of hard carbide phase,the hardness of the coating increases,the elastic modulus decreases,and the corrosion resistance is enhanced.In addition,with the increases of Cr/Al atom ratio from 1:2 to 2:1,the content of Al₄C₃ in the coating gradually increases while the content of Cr Al decreases,and the corrosion resistance of the coating gradually increases.When the alloy target Cr/Al atom ratio is 2:1 and the flow ratio of C₂H₂/Ar is1/4,the CrAlC coating exhibits the highest hardness and the best corrosion resistance.（2）The results of the study on the influence of annealing temperature on the performance of CrAlC coatings show that with the increase of annealing temperature from 700°C to 800°C,the contents of Cr₂₃C₆ and Al₄C₃ gradually increase.However,when the annealing temperature rises to 900°C,the content of Al₄C₃ decreases,and Cr₂₃C₆ changes into a small amount of Cr₇C₃ and Cr₃C₂,which is mainly attributed to the diffusion and volatilization of Al element with low melting point under high temperature annealing.After annealing at 800°C for an hour,the coating exhibits the highest hardness and elastic modulus,and has the best corrosion resistance.（3）Al/CrAlC multilayer coatings with different Al layer thicknesses were prepared.The results of the study on the influence of multilayer Al/CrAlC structure on the performance of CrAlC coatings show that the deposited coatings were mainly Cr₂C phase and Al elemental,with the increase of Al layer thickness,Al content increases,Cr₂C content decreases,and the corrosion resistance of the coating decreases.After annealing at 800°C for 1 h,the content of Cr Al phase in the coating increases with the increase of Al layer thickness,and the corrosion resistance of the coating gradually improves.When the Al layer thickness increases to 0.15μm,the annealed coating mainly exhibits Cr₅Al₈ phase and a small amount of Cr₂Al C phase,which has the best corrosion resistance.