| The domestic development in precision devices electroforming starts relatively late, as to stable molding process being rather scarce. Especially the r&ds of the cold-shield material used in the second generation of infrared detector’s dewar and the miniature corrugated pipe are more less. At present, research to the cold-shield material and the miniature corrugated pipe is still in the primary stage. There are many problems in the precision thin-wall parts such as the low accuracy, big stress, and instable organization composition, physical and mechanical performance etc. So it is particularly important that independently to investigate stable molding process method to produce the cold-shield material and the miniature corrugated pipe which have high precision, stability organization composition and good mechanical properties. But the conventional processing methods can’t satisfy the precision devices requirement.Therfore, adopting special process methods for its production is very necessary, and the electroforming is one of the most ideal methods to produce such precision devices.Ni-Co alloy material has been applied in electroforming technology in taking the place of the traditional pure nickel for its good physical, chemical and mechanical properties such as wear resistance, corrosion resistance, high rigidity, high hardness and electric magnetic. Stable electroforming Ni-Co alloy technological process is achieved in this way. The cold-shield material and the miniature corrugated pipe are successful prepared consistent with the actual production requirements. The influence of electroforming Ni-Co alloy process conditions on the casting layer’ organization and properties has been discussed. The influence of sulfamate root to Ni-Co alloy anomaly codeposition behavior has been analysed and the electrodeposition Ni-Co alloy anomaly codeposition mechanism has been discussed. Meanwhile the finished products of the cold-shield material and the miniature corrugated pipe have been tested and investigated.The main subjects and results in this dissertation are as follows:The cold-shield material with cobalt content in7%to15%,the biggest wall thickness uniformity less than10%, the surface roughness Ra≤0.4and its micro-hardness HV>400can be prepared by electroforming Ni-Co alloy from Sulfate electrolyte. Composition of the casting solution and operating conditions are as follows:NiSO4·6H2O250-350g/L, CoSO4·7H2O9-15g/L, NaCl20-25g/L, H3BO335-45g/L, Surfactant0.05-0.1g/L, Complexing agent TN15-15g/L, Additive TN20.08-0.15g/L, Dk2-6A/dm2, pH value4-5, Temperature55-65℃, magnetic stirring.In the above technological process, the concentration of CoSO4·7H2O has certain influences to the electroforming layer’s cobalt content, morphology, stress, hardness and microstructure. With the increasing of the Co2+concentrations in the electrocasting liquor, the casting layer’s cobalt content will increase, the casting layer’ stress and micro hardness shows ascendant trend, and the casting layer’s grains became much smaller, more uniform and flat. The casting layer’s diffraction peaks are gradually widened, but no other phase diffraction peak appears when the Co2+concentrations increasing in the electrocasting liquor. The current density has great influences on the casting layer’s cobalt content and stress. With the increasing of the Current density, the casting layer’s cobalt content has a down trend; the Casting layer’s stress has the trend of at first increasing, then decreasing; the Casting layer’s micro hardness is slightly decreased and the casting layer’s grains increase gradually.No other phase diffraction peak appears in the casting layer’s diffraction figure and the diffraction peaks (111),(200) all appear the phenomenon of strengthening when the current density increasing. The casting layer’s Crystal nucleuses have the preferred orientation and its growth direction are mainly along the [100], partly along the [111] direction. The additive TN2and TN3have great influence on the casting layer’s grain size. The impacts of additives on the casting layer’s stress have a relationship with the additives’ species. TN2can make casting layer produce pressure stress; the casting layer’s stress gradually decreases when its concentration increasing. But additive TN3can make casting layer produce tensile stress; the casting layer’s stress gradually increases when its concentration increasing.The additive TN2which is synthesized independently can make casting layer morphology more bright and flat. It can reduce casting layer’s stress at the same time, and it can improve the micro hardness of casting layer. It has stable performance and good application prospect in the electroforming Ni-Co alloy from Sulfate electrolyte.The additive TN3can make the casting layer full bright and increase the casting layer’s micro hardness obviously. But we should be careful when we use it because of its join will increases the cast layer’s stress.The miniature corrugated pipe which has low Leak rate, high fatigue limit (more than2×105), high wall thickness uniformity (0.03mm±0.0040), uniform Elongation (2.5mm±0.3) and high stiffness(＞700g/mm) can be prepared by electroforming Ni-Co alloy from sulfamate electrolyte. Composition of the electrocasting liquor and operating conditions are as follows:Ni(SO3NH2)2·4H2O500-650g/L, NiCl2·6H2O10-15g/L, Co(SO3NH2)2·4H2O,10-16g/L, H3BO335-40g/L, Surfactant0.15-0.2g/L, pH value3.5-4.5, Temperature40-50℃, Stir Magnetic stirring, Pulse peak current density2-6A/dm2.If the miniature corrugated pipes which have a bright surface and higher stiffness are needed, the additives HP1and HP2should be added into the electrolyte.The concentration of Co(SO3NH2)2·4H2O has certain influence to the electroforming layer’s cobalt content, morphology, hardness and microstructure. With the increasing of the Co2+concentrations in the electroforming solution, the casting layer’s cobalt content will increase, the casting layer’s grains get refinement, and the micro hardness increases continuously. The casting layer’s crystal structure isn’t obvious changed, but all diffraction peaks are widened and the Crystal (200) is reduced when the increasing of the Co2+concentrations in the electroforming solution. The Pulse peak current density has great influences on the casting layer’s cobalt content and morphology. When the pulse peak current density increases, the casting layer’s cobalt content and cauliflower crystal cell continuously increase; the crystal cells’ interfaces gradually become clearer. The casting layer’s microscopic hardness and microstructure are less affected by the increasing of the pulse peak current density. The additive HP1and HP2have great influence on the casting layer’s morphology, microscopic hardness and microstructure. The additive HP1has the function of refining grain and the additive HP2has a very good leveling effect for the casting layer. Both of them can make the casting layer’s microscopic hardness strengthen and diffraction peak width. The additive HP1has selectivity to the casting layer’s crystal plane and the casting layer’s crystal nucleus mainly grows along the [100] direction. But the additive HP2has different selectivity to the casting layer’s crystal plane. The casting layer’s crystal nucleus mainly grows along the [111] direction. The miniature corrugated pipes are produced by using pulse current from sulfamate electrolyte. To a great extent, the pulse current can enhances the casting solution’s dispersion ability and penetration power. The additive HP1and HP2that are developed by ourself have a very high application value and can increase the casting layer’s surface smoothness and microscopic hardness.Both in the Sulfate system and sulfamate system, Ni-Co alloy electroforming all belong to abnormal codeposition. The existence of the sulfamate root will aggravates the Ni-Co alloy anomaly codeposition phenomenon for it is a weak field ligand. Based on the crystal field theory, two mechanisms of Ni-Co alloy anomaly codeposition are discussed.(1)The weak field ligand existence will lead to the cobalt ions d orbital electron split for its stronger adsorption ability. The Co2+and weak field ligand will easily form octahedron high spin complex. It is easier decomposition than the complex which formed by Ni2+with the weak field ligand. So the Co easier electroplating prior to Ni.(2) due to the precipitation of the H+on the cathode,the pH value of the cathode local is increased. The Co(OH)2colloids which are easy formed from OH-and Co2+can adhere to the cathode surface. The reduction reaction of Nickel ions will be restrained by the Co(OH)2colloids.The cold-shield material used in the second generation of infrared detector’s dewar andd the miniature corrugated pipe used in self-adjusting throttling refrigeration are successful development. These technologies fill the domestic blank on the research techniques of precision devices and independently guarantee production of the major defense equipment key parts in China. The military career and precision manufacturing industry development in our country are promoted by this research, so it has great significance.The main innovation points of the research work:(1) The stable processes of the sulfate system and sulfamate system electroforming nickel cobalt alloy have been independently developed.(2) The additives which have good performance and good stability are developed.(3)The nickel cobalt alloy anomaly codeposition mechanism has been discussed on the basis of the theory crystal field.It has reference value for future research.(4) The electroforming nickel cobalt alloy technique has successful applied to the research of the precision devices.This technique fills the blank in domestic and breaks the foreign blockade. |
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