Electroless Composite Plating Ni-P/Ni-P-PTFE Double Coating

Electroless Ni-P alloys are the surface protective technology that have developed rapidly and been widely used in recent years. The composite sedimentary of the PTFE powder which with self-lubrication to Ni-P alloy formed a Ni-P-PTFE composite coating of low friction coefficient, this study prolonged the service life of Electroless Ni-P alloys and expanded their application. As the additives which with self-lubricating composite platings, the particle size of the PTFE powder and its dispersiveness in the chemical plating solution have direct impact on the technology of Ni-P-PTFE composite electroless plating and the performance of the coating ,so that, it is important to our production practice and academic research. The main work of this thesis is: (a) The combination conditions of the two surfactants system containing cetyl-trimethylammonium bromide and OP Emulsion searched, and the effects of the concentration ratio of the two surfactants on the improvement of PTFE powder hydrophobic were discussed through the full-factor tests. (b) The effects of the PTFE concentration in the plating solution on the deposition rate of the technology of Ni-P-PTFE composite electroless plating and the performance of the coating were studied, at the meantime the PTFE content in the coatings were tested. (c) The effects of Ultrasound on the technology of Ni-P-PTFE composite electroless plating and the performance of the coating were studied, and then the effects of Ultrasound on the structure of the Ni-P-PTFE composite coatings and the morphology of the coatings were analyzed through X ray diffraction and SEM. (d) By experiments the improvement of the properties of Ni-P-PTFE Electroless Plating were discussed when Ni-P/Ni-P-PTFE composite electroless plating technology was used.The experimental results and theoretical analysis show as below.(1)Cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and nonionic surfactant alkylphenol polyoxyethylene ether (OP emulsifier) should decrease the PTFE powder hydrophobic, and it is better to use the two surfactants together. The best concentration ratio was OP～2.0mL/L; CTAB～15mg/L.(2) The PTFE powder have very low friction coefficient and good self-lubricating, so it can greatly improve the abrasive resistance of the Ni-P-PTFE composite coatings . The wear rate of Ni-P-PTFE composite coatings could be reduced to 70% of Ni-P coatings, when impressed ultrasound it can be reduced to 60% ,but the hardness, bonding force, porosity of the coatings were all reduced . When the PTFE concentration is 10g/L, the Ni-P-PTFE composite coating cam achieve high hardness and dense structure.(3) Using ultrasound could improve uniform dispersion of PTFE powder in the plating bath and could improve performance of Ni-P-PTFE composite coating. Using ultrasound,the deposition rate of Ni-P-PTFE alloys could be increased by about 1.35 times.Using ultrasound could make microhardness, bond strength, abrasion resistance, corrosion resistance of Ni-P-PTFE composite coating could also be improved. The XRD results suggested that the amorphous structure of alloy transform into amorphous and microcrystalline mixture structure of of alloy. And the SEM photos showed that the composite deposition layer was layered growth macroscopically and cellular growth in the catalytically active point microscopically. Using ultrasound, the granular protuberance on the coatings become more fine-grained and more uniform, the densification degree of coating microstructure was further increased, and the bonding force become more stronger.(4) The electroless composite plating Ni-P/Ni-P-PTFE double coating could make up for the defects of the Ni-P-PTFE composite coatings performance. The comprehensive properties of the double-layer composite coatings were best when it is 60min (Ni-P bottom) / 60min (Ni-P-PTFE surface).