| Electrodeposition method has attracted much attention because of its simple equipment, flexible operation, and prepared coatings with excellent performances. At present, there are more mature researches on application of electrodeposited binary alloys, while the study on ternary alloys, electrodepositing S135drill pipe materials is relatively limited. At the same time, amorphous materials are different from crystalline materials with excellent properties because of their special structure. Therefore, research on the structures and properties of ternary amorphous alloys electrodeposited S135drill pipe materials and prepared by electrodeposition method will have certain guiding significance and application value.In this paper, an orthogonal test method was adopted to optimize electroplating parameters. The amorphous Fe-Ni-W alloy coatings were successfully made on the surface of S135drill pipe steels by using the optimized formula. In order to further improve process formula, ICP-AES was used to explore the influence of pH of plating solution, current density and additive content of sodium citrate on composition, microhardness and deposition rate of Fe-Ni-W alloy coatings. XRD, SEM, DSC and hardness test were also used to analyse the effect of different heat treatment on the microstructure, micro-morphology, crystallization characteristic and properties of the amorphous Fe-Ni-W alloys. In addition, electrochemical experiment and weight loss method were used to research corrosion behavior of samples of S135drill pipe steel which were electroplated Fe-Ni-W alloy coatings in3.5%sodium chloride solution, simulated formation water and high temperature and high pressure corrosive environment respectively.The electroplating process results showed that the optimized preparation process of electrodepositing Fe-Ni-W alloy coatings were obtained. That was as shown:FeSO4·7H2O10g/L, NiSO4·6H2O40g/L, Na2WO4·2H2O90g/L, plating temperature is65deg C, plating solution is6pH, current density is15A/dm2, Na3Cit·2H2O30-40g/L, the right amount of additives, electroplating time is50min.S135steel specimens electrodeposited with Fe-Ni-W alloy coatings after different heat treatment tests. It found that the solid solution of Ni3Fe and Fe7W6was precipitated from alloy coating after heat treatment at150deg C and alloy hardness increased. When heat treatment temperature was250deg C, diffraction peak became more sharp, and alloy was further crystallizing, precipitating solid solution of Fe7W6accompanied with hard brittle phase particles desolution. At this point, alloy was mixed crystal dispersion state and microhardness reached the maximum of506HV. Temperature continued to increase, phase was gradually precipitated from Fe7W6solid solution, and alloy had eventually transformed from amorphous to crystalline. At this time, dispersion structure disappeared, and grains grew rapidly under the high temperature, coating hardness fell sharply. By the above range of structure and hardness changes, ideal high hardness about alloy coating on the surface of S135drill pipe steel was obtained under the process formula of preparation for Fe-Ni-W amorphous alloy coating after heat treatment by250deg C.S135steel specimens electrodeposited with Fe-Ni-W alloy coatings after different corrosion tests. The experimental results indicated that passivation phenomenon appeared on the polarization curves of samples after heat treatment at250deg C in3.5%NaCl and simulated formation water, accompanied with wide passivation range and small passivation current density, and had strong ability of passivation. Learned from the Bode diagram, the impedance value of samples after heat treatment at250deg C were the largest, and phase angle closed to90degrees. Micro-topographies of high temperature and high pressure corrosion test showed that smooth cellular particles gradually became rough broken debris on the surface of samples with heat treatment at250deg C. In this process of corrosion, weightlessness was the least, and corrosion rate was minimal. Compared with other heat treatment conditions, S135steels electroplated Fe-Ni-W alloy after heat treatment250deg C had excellent corrosion resistance. |
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