Studies On Preparation Technology And Performance Of Ni-W-P Amorphous Alloy Coating

For the purpose of preparing high performance amorphous Ni-W-P alloy plating,this paper,on the basis of analyzing and studying of technology research status home and abroad,took full consideration of influence factors during the experiment,and discussed the preparation of high performance amorphous Ni-W-P alloy plating on copper substrate by using conventional electro-deposition method and jet-electro-deposition method.For the electro-depositing amorphous Ni-W-P alloy plating,this paper studied the performance and maintenance scheme of the plating solution,the influence of the composition and technological parameter of plating solution on the structure and performance of the amorphous Ni-W-P alloy plating,,the influence of introducing Tungsten and heat treatment temperature on the structure and performance of amorphous Ni-W-P alloy plating.For the jet-electrodeposited amorphous Ni-W-P alloy plating,the paper analyzed the influence of technological parameters on the composition and structure of the jet-electrodeposited amorphous Ni-W-P alloy plating,such as jet velocity,current density,temperature and pH value etc,and defined the structure and performance of Ni-W-P alloy plating before and after heat treatment.In addition,by combining flux progress and DCS,the author further studied the deep undercooling melt technique of Ni-W-P alloy,non-isothermal solidification crystallization kinetics law during this process,and the influence of plastic deformation on the crystal structure and crystallization activation energy of jet-electrodeposited amorphous Ni-W-P alloy plating.The results showed that for conventional electrodeposited amorphous Ni-W-P alloy plating,the optimum plating solution is NiSO4·6H₂O 16 g/L,Na2WO4·2H₂O 60 g/L,NaH₂PO2·H₂O 4 g/L,C₆H₅Na3O7·2H₂O 90 g/L,H3BO3 36 g/L and moderate saccharin and lauryl sodium sulfate.This plating solution shows excellent performance: the cathode efficiency is 32.52%,the average plating ability is 84.7%,the deep plating ability is 100% and the homogeneous plating ability is 47.68%.The optimized technological factors are: temperature 50±2℃,pH value 6±0.2,and current density 4±0.2 A/dm².The obtained Ni-W-P alloy plating is amorphous,which composition is Ni 70.94 wt.%,W 20.35 wt.%,and P 8.71 wt.%.Compared with Ni-P alloy plating,the introducing of tungsten makes Ni-W-P alloy plating have more homogeneous and smaller surface cell structure and higher deposition rate,with the crystallization initiation temperature as high as 429.2℃.The performances including thermal stability,corrosion resistance and hardness are all significantly improved.During the electro-deposition,with the increase of the content of sodium tungstate,the plating will be harder and the corrosion resistance will be better for a same structure.The deposition rate and the current efficiency will reach their maximum,8.2 μm/h and 32% respectively,when the sodium tungstate’s concentration gets to 70 g/L.When the content of sodium hypophosphite increases,the current efficiency will gradually drop,the corrosion resistance of the plating will be slowly enhanced and the scale of the surface cell structure will be reduced significantly.With the drop of hypophosphite’s content,the current efficiency gradually declines,and the alloy coating hardness also slightly decreased.The deposition rate can be 8.7 g/L when the sodium hypophosphite’s concentration is 10 g/L.With the increase of the content of sodium citrate,current efficiency and the plating’s hardness will also drop.When the concentration of the sodium citrate is 80 g/L,the deposition rate can reach its maximum,8.6 μm/h,and the plating’s corrosion resistance will be the best.With the increase of saccharin’s content,the hardness of the Ni-W-P plating will increase,and the corrosion resistance will be strengthened firstly and then weakened,and the scale of the surface cell structure will be reduced gradually.With the increase of the heat treatment temperature,non-crystallization plating starts crystallizing,and Ni3 P and Ni-W will be separated out,and the corrosion resistance will get worse.After 1h insulation at 700℃,The natural corrosion current of the coating is about 30 times that of the plating.When increase the heat treatment temperature,Ni-W-P plating’s hardness will increase firstly and then decrease.The hardness will reach its maximum,1099.2 HV,at 600℃,which is promoted nearly twice compared with the plated state.The better plating solution for the jet-electro-deposition amorphous Ni-W-P alloy is jet velocity at 3.33 m/s,current density at 25±0.2 A/dm²,temperature ranging 50±2℃ and the pH value at the range of 6.5±0.2.Then the amorphous Ni-W-P alloy plating is obtained,in which Ni is 79.24%,P is 13.96%,and W is 4.28%,whose nano-indentation hardness is 4.6 Gpa.After 1h insulation at 400℃,non-crystallization plating turn into crystalline,and the hardness of nano-indentation is 13.3 Gpa,which is significantly improved.For the jet-electro-deposition Ni-W-P alloy melt（W 3-5 wt.%,P 10-14 wt.%）,when the cooling rate increases from 10 K/min to 50 K/min,the degree of undercooling increases rapidly and the maximum value is 359 K.The increase of superheat can efficiently raise the degree of undercooling when superheat increases in the range from 20 K to 160 K.For the jet-electro-deposition amorphous Ni-W-P alloy（W 3-5 wt.%,P 10-14 wt.%）,it will start crystallization when the degree of cold deformation is more than 20%,and the crystallization temperature and the crystallization activation energy will gradually decrease with the increase of the cold deformation.