Study On Electroforming Process And Mechanical Properties Of Low Stress Nickel And Nickel-Cobalt Alloys

With the increasing of the size of x-ray focusing telescope,the mechanical properties of traditional electroformed nickel no longer meet the demand,and electroformed nickel-cobalt alloy with higher mechanical strength becomes the top candidate intead of pure nickel metal.However,nickel cobalt alloy produces higher internal stress than pure nickel in the process of electroforming,which is easy to cause lens deformation.In this paper,low internal stress nickel and nickel cobalt alloy electroforming process parameters,the relationship between internal stress and structure the electroforming process simulation were researchrd,which provide experimental basis and model for regulating the internal stress of lens.The effects of cobalt sulfamate content,current density and pH value on the internal stress of electroformed layer in sulfamic acid system were studied.The optimal conditions were as follows:nickel sulfamate 400 g/L,cobalt sulfamate 6 g/L,nickel chloride 5 g/L,boric acid 35 g/L,sodium dodecyl sulfate 0.5 g/L,pH=3.75,current density 1.40 A/dm~2.Compared with the pure nickel coating,the elastic modulus,non-proportional elongation strength,ultimate strength and hardness of the electroformed coating increased by 25.88%,23.74%,40.96%and 16.59%,respectively.The mechanical properties of the electroformed layer were significantly increased by process optimization.Then BP neural network algorithm was used to train the experimental data,and the mechanical properties of 2310 samples were predicted according to the training model.The optimal conditions were as follows:cobalt sulfamate content 4 g/L,pH=3.9,current density 1.65 A/dm~2.The mechanical properties of the electroformed layer were significantly increased by process optimization.By characterizing the microscopic morphology and crystal structure of the nickel electroformed layer,it was found that the coating gradually transformed into Ni{200}surface texture during the growth process.When the current density was reduced or the cobalt content of coating is increased,the surface of the electroformed layer became denser.With the increase of current density,the grain size of the coating gradually increased,while first increasing and then decreasing with the increase of cobalt content in the coating.The internal stress of electroformed layer was cumulative,which was closely related to the structure,composition and morphology of electroformed layer.The results showed that the internal stress increased with the increase of current density and Co concentration in electroforming solution.COMSOL was used to simulate the electroforming process of the X-ray focusing mirror with average current density of electroforming setting to 2.00 A/dm~2.The results showed that the maximum current density difference along upright of X-ray focusing mirror surface was 1.15 A/dm~2 without auxiliary cathode.And the maximum difference of electroforming layer thickness was 127.85μm with the average thickness up to222.01μm;After adding the auxiliary cathode,the maximum current density difference was about 0.06 A/dm~2,and the maximum thickness difference was 6.00μm.The uniformity of current density distribution on the surface of electroformed layer was significantly increased through adding auxiliary cathode.