Study Of The Mechanical Properties,high Temperature Oxidation Behaviour And Corrosion Performance Of CoCrNi-based Multi-principal Alloys

Compared to conventional alloys,multi-principal alloys are based on a new alloy design concept that has re-expanded the knowledge and understanding of phase components in alloys.Over the past century,due to its high strength,high toughness and good wear resistance,it has gradually become a research hotspot and is expected to become a potential structural material for engineering applications.At present,research into multi-principal alloys is still at a relatively preliminary stage of exploration.Corrosion,as the main mode of failure of metallic materials,is one of the factors that must be considered as a priority in the development of new structural materials.The corrosion of metals is divided into chemical corrosion and electrochemical corrosion according to the occurrence of the reaction with or without the generation of electric current.Chemical corrosion is generally the action of a corrosive medium on the surface of a material,with no current generated in the reaction,most commonly through the high temperature oxidation of the material.Electrochemical corrosion is the surface damage caused by the gain or loss of electrons in an electrolyte solution,during which an electric current is generated.This paper systematically investigates the reaction process and mechanism of CoCrNi multi-principal alloys when these two types of corrosion occur.Through comprehensive microstructural characterisation,high temperature oxidation experiments and electrochemical corrosion experiments,the relationship between the microstructure and properties of the alloy is elucidated and the following main conclusions are drawn.(1)In CoCrNiAlxY(0.02)alloy,the crystal structure of the alloy changes from FCC solid solution to BCC solid solution when aluminum content changes from 0.2 to 1.4;With the increase of Al content in the alloy,the strength of the alloy is improved,and the expansion rate of the alloy is reduced.When the Al content is 0.6,the hardness is 418.5hV,the yield strength is 482.4(±5)MPa,the ultimate compressive strength is 1758.7(±5)MPa,and the compression rate is 23%.At this time,the alloy has relatively good comprehensive mechanical properties.(2)The addition of Al content can improve the high temperature oxidation resistance of the alloy,but excessive Al will cause the peeling off of the oxide film and lose the protective effect on the alloy matrix.CoCrNiAlxY(0.02)series alloy is oxidized at 1200℃ for 60 h.CoCrNiAl0.6Y(0.02)alloy has the lowest Kp value of 4.60×10-6 mg/(cm2·h),and has the best high-temperature oxidation resistance.(3)Electrochemical results of CoCrNi alloy in 3.5wt.%NaCl solution show that the compactness and stability of passivated film formed on the surface of CoCrNi alloy annealed at 600℃ are better than those of as-cast and cold-rolled,and the MEA of CoCrNi annealed at 600℃ is more resistant to pitting corrosion.The solution strengthening effect of TiC can improve the corrosion resistance of CoCrNi alloy.However,the corrosion resistance of CoCrNi alloy decreases when the addition amount of TiC exceeds the solubility of TiC in the alloy.