Research On The Performance And Influence Factors Of Mwcnts Reinforced Ni-W Composite Coatings

With continuous increasing demand for energy in production and daily life,the exploitation and production of oil and gas shifted to deeper layer and ocean.Environment of the oil and gas well is turning worse,and extreme conditions are increasing.Therefore,maintaining the safety and service life of the tools and equipment is critical for the production of oil and gas.In the corrosion protection technologies,surface treatments are widely employed due to their cost-effective.As a typical method,electrodeposition shows a great potential in electronics,aerospace,chemical and other fields.In recent years,nano-composite electrodeposition is becoming an important development in plating fields.The nano particles are firmly and uniformly embedded into the metal coatings,and various properties of the composite coatings are improved.During the numerous metal plating,nickel tungsten alloy has already attracted much attention for its hardness,corrosion and oxidation resistance.Furthermore,Ni-W alloy deposit is recently developed as one of the surface treatments to substitute the environmentally harmful hexavalent hard chromium film.However,undesired residual stress frequently increases with the increasing of hardness and wear resistance due to low current efficiency and hydrogen evolution reaction on cathode.In severe cases,micro-cracks were found on the deposit surface.As an ideal reinforcement,multi-walled carbon nanotubes were considered,and MWCNTs composites exhibited high modulus,high strength and friction reducing lubrication.MWCNTs composite deposits showed great potential in high temperature,oxidation and corrosion resistance.In this paper,we first systematically studied the preparation and properties of MWCNTs reinforced Ni-W composite deposits.The effective dispersion method and preparation systems of Ni-W/MWCNTs coatings were developed.Firstly,the dispersion stability and aggregation scale of MWCNTs in Wegramyan plating bath was investigated by technologies,such as spectrum,Zeta potential,particle size analysis and electrochemical polarization curves.The adding of surfactants can improve the dispersion stability of MWCNTs in the plating bath to a certain extent,and reduce the aggregation scale at same time.From the analysis of cathodic current efficiency and deposition kinetics,the anionic surfactant sodium dodecyl sulfate can improve the dispersion stability of MWCNTs without decreasing the current efficiency.Polyethylene imine polymer like dispersant can significantly improve the dispersion stability of MWCNTs in the electrolyte solution,and significantly reduce the size of the aggregates.However,PEI directly mixing would seriously inhibit the deposition process on cathode surface.The dispersion stability of MWCNTs in the plating bath will be improved without decreasing the current efficiency by the pre-coated of MWCNTs with PEI.Ni-W/MWCNTs composite deposit was fabricated on the C45 carbon steel surface by DC electrodeposition.Effects of surface coating on composition and structures were studied before and after the incorporation of MWCNTs.As a result,surface morphology of the composite coating is more compact.Besides,grain size of the surface film is decreased,and the co-deposition of MWCNTs has greater influence on the deposition of tungsten.On the other hand,the influence of the field emission effect of MWCNTs leads to a more rough composite coating surfaces.The results show that the hardness and bonding strength of the Ni-W/MWCNTs composite coating are improved,and the electrochemical corrosion resistance of the coating is excellent.In order to further improving the properties of the coated specimen,Ni-W/MWCNTs composite deposits were fabricated on the C45 steel surface by pulse electrodeposition technique.The effects of pulse parameters on the content of MWCNTs,tungsten and the micro-hardness of the coatings were discussed.Besides,the relationship between the pulse parameters and coating properties was optimized by response surface method,and the optimal pulse parameters were obtained.Surface morphology of the as-prepared Ni-W/MWCNTs composite coating with pulse current is smooth,dense and uniform.Compared with the direct current electrodeposition sample,the average surface roughness is reduced,and the film grain size is further decreased.When the concentration of MWCNTs in the bath is 0.1-0.3g/L,composite coatings have a smaller crystal composition from 8.1-8.3nm.From the results of XPS,both metal and oxidation state of Ni,W was found.After etching,the SEM shows that MWCNTs and the metal matrix can be well fused,and there is no obvious interface.Finally,the physical and mechanical behaviors of pulsed electrodeposition deposits showed that the porosity and friction coefficient of the film were further decreased,and the hardness and adhesion were further increased.The tests of corrosion and electrochemical curves exhibited that the as-prepared coatings presented excellent corrosion resistance in different pH NaCl solution.Dispersion stability of the PEI-coated MWCNTs in the plating bath is significantly improved without decreasing the cathode efficiency.Ni-W/MWCNTs composite coating with high MWCNTs content was prepared by pulse plating on the surface of C45 steel.When the concentration of MWCNTs in the bath was 0.3g/L,the amount of MWCNTs in the composite coating was nearly 17wt.%.As a result,the uniform region of the film layer is more distinct than that of the micro convex region,and the grain size is smaller.In the experiments of bending and extrusion,squeezing of the specimen at 180 degree does not cause the surface film to be peeled off or the micro cracks produced.Therefore,the MWCNTs composite coating exhibits excellent strength and plasticity with eliminating the influence of residual stress.Besides,the composite coating with high content of MWCNTs exhibits similar corrosion resistance.In final,the corrosion resistance of C45 carbon steel coated with the composite coating was investigated by simulating several representative conditions of high temperature,high pressure,carbon dioxide and hydrogen sulfide in the process of oil and gas production and transportation.Results show that the Ni-W/MWCNTs composite coating has excellent corrosion resistance,and effectively prolongs the service life of C45-like common steel.