Study On Preparation Process Of Fe-Cu/Ni Composite Powders With Core-shell Structure For Powder Metallurgy

In order to solve the problems of compositional segregation and difficulty in alloying due to the long diffusion distance between the powders of mechanically mixed composite powder.In this paper,Fe-Cu,Fe-Ni and Fe-Cu-Ni composites powders with core-shell structure were prepared by electroless plating.The effects of process parameters?reducing agent concentration,complexing agent concentration,temperature and pH?on the plating rate,the microstructure of the coating,the stability of electroless copper plating solution and the phosphorus content of electroless nickel plating were studied by orthogonal experiment combined with single factor experiment.Explore the key control points of electroless plating process for obtaining excellent core-shell composite powder.It provides experimental and theoretical basis for the preparation of Fe-Cu/Ni composite powder with core-shell structure by electroless plating.Research indicates:?1?For the preparation of Fe-Cu composite powder with core-shell structure,the order of influencing factors of plating rate is pH,temperature,concentration of complexing agent?EDTA-2Na?and concentration of reducing agent?HCHO?.Within the range of pH,temperature,the concentration of EDTA-2Na and the concentration of HCHO are 12 to 13,30 to 50°C,9 to 15 g/L and 10 to 14 ml/L,when the pH is 12.5,temperature is 40°C,the concentration of EDTA-2Na is 12 g/L and the concentration of HCHO is 10 ml/L,the electroless copper plating speed of iron-based powder reached a relatively fast level and the stability of the plating solution is good,the coating is tightly combined with the substrate,the coating is complete and the composition is evenly distributed.It was found that the main factor affecting electroless copper plating was pH,which had a great influence on the reduction ability of HCHO.When the pH is too low,the plating speed is slow and the coating thickness is too thin to completely coat the matrix powder,but when the pH is too high,the stability of the plating solution is poor to be easily decomposed and broken.?2?For the preparation of Fe-Ni composite powder with core-shell structure,the order of influencing factors of plating rate is:concentration of reducing agent?NaH₂PO₂·H₂O?,temperature,pH and concentration of complexing agent?C₃H₆O₃?.Within the range of the concentration of NaH₂PO₂·H₂O,temperature,pH,concentration of C₃H₆O₃ are 15 to 25 g/L,75 to 85°C,8 to 9,12 to 20 ml/L,when the concentration of NaH₂PO₂·H₂O is 15g/L,temperature is 85°C,pH is 9 and the concentration of C₃H₆O₃ is 12 ml/L,the electroless nickel plating rate of iron-based powder reached a relatively fast level,the coating is tightly bonded to the substrate and the coating is complete.The composition is evenly distributed and the phosphorus content in the coating is low.It is found that the effect of NaH₂PO₂·H₂O concentration on electroless nickel plating is much greater than other factors.With the increase of NaH₂PO₂·H₂O concentration,the plating rate increases,the phosphorus content in the coating increases,and the coating quality decreases.?3?Fe-Cu and Fe-Ni composite powders were successfully prepared by optimized electroless copper plating and nickel plating process,and they have obvious core-shell structure,uniform coating composition.The Fe-Cu-Ni composite powder was directly prepared by secondary electroless plating,and the Cu and Ni coatings were successively plated,which verified the practicability and extensiveness of the optimized process.