Study On The Structure And Properties Of Electroless Nickel Phosphorus NanoAL₂O₃ Composite Coatings

The functions of electroless composite deposits were introduced in this paper.The solution constitutes and its functions of electroless nickel phosphorus were introduced ,as well as their influence on the rate and properties of the coatings were studied in this paper. The configuration and properties of electroless nickel-phosphorus and electroless nickel-phosphorus composite Al2O3 deposits were investigated.Orthogonal experimentation was used to choose the technical parameter. The bath contained the main constituents: nickel sulfate (25g/l),sodium hypophosphite(25g/l),lactic acid (20ml/l),sodium acetate (10g/l),acetum(10m/l), the bath temperature was kept at 85 ℃ with the PH in range of 4~5.PH had great influence to the solution, technology of electroless nickel-phosphorus and deposits characteristics. In acid solution, the deposit rate increased with the PH rising up and reached maximum when the PH was adjusted to 4.5 .The temperature of the bath was an important dynamic parameter. Temperature affected not only the deposit rate but also the characteristics of the coatings. The rate increased quickly with the temperature exceeding 60℃. When temperature was higher than 90℃, the solution of electroless nickel-phosphorus was easily decomposed.In the bath, lactic acid and nickel ion were created complex compound that made the solution more stable, and the surface of workpiece could be actively increased .The deoxidate capability of sodium hypophosphite could be increased with its concentration going up .The deposits rate reached maximum when Ni2+/H2PO2- reached 0.4, the concentration of hypophosphite was continued going up ,there would be different concentration between the workpiece surface and inner of the bath ,which could induce the bath to decompose .The structure of the deposits was studied using X-ray diffraction technique. The deposits was a metastable supersataration as deposits condition ,whichcould be microcrystalline as the P content below wt3% ,while those in the Higher range were mixture of microcrystalline and amorphous phase, when the P content exceeded 12%,the deposits could be as amorphous. With the P content rising up ,the structure of the deposits was described as :microcrystalline-mixture of microcrystalline and amorphous -amorphous phases.The structure of the deposits was converted from amorphous phase and mixture of microcrystalline and amorphous into crystallization after heat treatment. Through heat treatment,the deposits hydrogen brittleness could be eliminated and the binding energy could be improved. The deposits microhardness was increased from HV300 as deposits condition to HV900 after heat treatment because of horniness precipitate Ni3P , while eletroless nickel-phosphorus composite Al2O3 deposits microhardness was increased from HV600 to HV1050.Deposits were dipped in acidic ,litmusless and alkalescent medium, its corrosion resistance was better in alkalescent medium than in the acidic, and the high P content was better than the low. The result was related to the amorphous phase. The deposits structure of high P content was amorphous which was single-structure ,the deposits was a definite indication of the lattice disorder .With good wear and resistance high temperature ,the composite deposits had been used in many industrial areas. Owing to new materials ,the electroless technology had a triumph prospects.