Study On Preparation Process And Microstructure And Properties Of Microelectroformed Bimetallic Capillary Tubes

Capillary is widely used in aerospace,consumer electronics and biomedicine.However,due to its small size,high dimensional accuracy and surface requirements,traditional forming technology is difficult to meet its preparation requirements.Micro electroforming technology is widely used in precision manufacturing industry because of its high degree of freedom and accuracy.In this study,a method for preparing Ni-Cu bimetallic capillary based on self-made mandrel was proposed by micro electroforming technology,and the feasibility of preparing capillary by micro electroforming was explored.Firstly,the effects of electrolyte temperature and p H value on the electrocrystallization behavior of Ni and Cu deposition layers were studied,and the optimal process parameters for electrodepositing Ni and Cu were obtained using single factor and orthogonal experiments;Secondly,the influence of the size of shielding baffle on the thickness distribution uniformity of casting layer was studied by combining numerical simulation with experiment;Finally,the samples after electroforming were treated,and the effects of different heat treatment temperatures on the properties of Ni-Cu bimetallic capillary were discussed.The main conclusions are as follows:Successfully prepared Ni Cu bimetallic capillary tubes with an inner diameter of0.5 mm,a length of 50 mm,and no impurities on the inner wall.The electrolyte formula and optimal process parameters for electroforming Ni on Sn core mold are:nickel sulfate 300 g/L,nickel chloride 40 g/L,boric acid 40 g/L,current density 6 A/dm~2,electrolyte temperature 60℃,pulse duty ratio 0.6,stirring speed 400 r/min and electrolyte p H 4.5;The electrolyte formula and optimal process parameters for electroforming Cu are:copper pyrophosphate 65 g/L,potassium pyrophosphate 300 g/L,potassium sodium tartrate 20 g/L,current density 3 A/dm~2,electrolyte temperature35℃,pulse duty ratio 0.5,stirring speed 300 r/min and electrolyte p H 9.Ni and Cu electrocrystallization is carried out through a three-dimensional nucleation and growth mechanism controlled by diffusion.As the electrolyte temperature increases,the current efficiency of Ni deposition process is improved;As the p H value of the electrolyte increases,the surface of the cast Ni layer gradually becomes fine and uniform,with a decrease in roughness and an increase in hardness.When the electrolyte temperature is 35℃,the electrodeposition efficiency of Cu is the highest;The increase in electrolyte p H promotes copper deposition..When t/t_m<1,the nucleation mode of Ni electrodeposition is continuous as the electrolyte temperature increases.When the temperature is 60℃,it is instantaneous nucleation;As the p H value and power supply voltage of the electrolyte change,the data points undergo a transition from instantaneous nucleation to continuous nucleation.Within the same range,the nucleation mode of Cu electrodeposition changes from continuous nucleation to instantaneous nucleation with the increase of electrolyte temperature and the decrease of p H value,and the data points change from instantaneous nucleation to continuous nucleation with the change of power supply voltage.When t/t_m>1,the nucleation mode of the sedimentary layer is instantaneous nucleation.The best parameters of shielding baffle for electroforming Ni on Sn mandrel are:inner hole length 30 mm,length 85 mm and thickness 15 mm;The best shielding baffle parameters for electroforming Cu are:inner hole length 30 mm,length 85 mm and thickness 16 mm.The variation coefficients of Ni,Cu,and Ni Cu layers cast with the optimal shielding baffle during the electroforming process are 7.84%,5.9%,and 7.67%,respectively,which is 54.23%,50.12%and 62.96%lower than that without shielding baffle.Because there are many residues on the inner wall of capillary after demoulding of Sn mandrel,hollow capillary can not be obtained,so the mandrel is replaced by self-made mandrel and Ni-Cu bimetallic capillary is successfully prepared.The prepared Ni-Cu bimetallic capillary was heat treated.The results showed that when the heat treatment temperature was 400℃,the surface quality of the capillary was the best,and the hardness value was the highest,which was 254.32 HV.With the increase of the heat treatment temperature,the diffusion area of the interface between Ni and Cu gradually increased,and the interfacial bonding force also increased,reaching 151 m N at 600℃.This study solved the problems of uneven deposition layer thickness and difficulty in core mold removal in micro electroforming technology,successfully prepared Ni-Cu bimetallic capillary tubes,and explored feasible methods for preparing bimetallic capillary tubes.