Research On Electrolytic Etching Technology Of Nickel-Based Superalloys For Small Pores

Nickel-based superalloys based on nickel,behave well in strength,oxidation resistance,corrosion resistance in the range of 65°C to 1000°C.Due to high strength,high toughness,and other characteristics,the traditional methods are limited when machining little holes.Therefore,further study on machining small pores on nickel-based alloy is of great significance.Electrolytic machining works by anode dissolution to remove materials so that to obtain products that meet the size and shape requirements.The technology is relatively mature and can overcome the disadvantages of traditional methods when machining superalloys.In this paper,the mask combining with fixed-double cathode are used to machining small diameter through holes in nickel-based alloys.The specific contents include establishing the electrolyte system,obtaining the optimal machining parameters,analyzing the anode dissolution process and mechanism,and discussing the possibility of electrolyte circulation.（1）The performance of the three electrolyte of sodium chloride,sodium nitrate and cerium ammonium nitrate is analyzed by electrochemical method,and the processing speed and small pores processing effect of nickel-based superalloy under the three systems are compared.Due to the great machining accuracy and surface quality,cerium ammonium nitrate is proposed as the electrolyte system for nickel-based alloy machining.（2）Sodium chloride,sodium nitrate,sodium chlorate,nitric acid,hydrochloric acid and tartaric acid are taken as the research object.Comparing the effects of different additives on the electrochemical behavior of nickel-based alloy anode dissolution,it shows that in the cerium ammonium nitrate system,nitric acid can effectively improve the processing speed and processing accuracy.Through single factor experiment and orthogonal experiment,the optimal process of electrolytic machining is obtained as cerium ammonium nitrate 16%,nitric acid 1mol/L,current density 50A/cm²,temperature 35℃.（3）The electrochemical reaction process and the anodic dissolution mechanism are studied by experimental method and theoretical simulation.The electrode reaction process in electrolytic machining is analyzed,and the mechanism of anode dissolution is explored.It is found that the cathode Ce⁴⁺is reduced to Ce³⁺during electrolysis,meanwhile hydrogen is produced.While the surface of the anode undergoes selective corrosion,with the extension of the electrolysis time,the pits are superimposed on each other eventually tend to be flat,and there is no residual corrosion product on the anode surface.The COMSOL simulation results show that the distribution of the flow field has a great influence on the shape of the little holes,and the electrolyte flow parallel to the anode surface is not conducive to the machining of little holes with a certain depth.（4）Research on the recycling performance of electrolyte anounces that the longer the electrolyte is used,the worse the machining effect will be.The consumption of the Ce⁴⁺reduces the machining speed.In order to realize the reuse of the electrolyte,the electrolytic machining waste liquid is treated by double-cell anodic oxidation.It is found that the machining speed is 10%higher than that before oxidation.