| Electrodeposition technique has been widely used in steel protection by imparting the substrate surface with excellent physical and chemical properties without changing their mechanical properties. However, it's often existing potential difference between the electrodeposition coating and the substrate, When the coating surface is partially damaged or has local defects, which providing direct paths for corrosive species to penetrate through the coating to reach the substrate, Therefore,directly contacted coating and substrate would represent a galvanic cell at the interfaces and the galvanic corrosion might happen between them. What's more, If the coating possess more positive electrode potential than the substrate, the corrosion of substrate can be severely accelerated and the protective capability of coating might be weakened. So the study of the galvanic behavior between the coating and substrate is very important for reducing the loss of corrosion and the proper use of materialsElectrodeposited Ni-W-P alloy has characteristics of high hardness, high wear resistance, high thermal stability and good corrosion resistance, which has been used for the corrosion and wear resistance of the oilfield equipment. However, up to now,no studies have examined the galvanic corrosion processes of electrodeposited Ni-W-P alloy. For the purpose of making better use of Ni-W-P alloy. It's necessary to study the galvanic corrosion behavior between the Ni-W-P coating and the substrate, In the present study, the galvanic corrosion behavior of Ni-W-P coating when coupled to the iron-based alloy substrates of N80,P110,J55,35 Cr Mo in 3.5 wt% Na Cl aqueous solution was investigated in detail, and it also lays down an important theoretical basis for the application of Ni-W-P alloy. The more research work was as follows:(1) The galvanic corrosion behavior between the Ni-W-P alloy and iron-based alloy of N80, P110, J55 and 35 Cr Mo in 3.5 wt% Na Cl aqueous solution was systematic studied by the weight loss test and electrochemical measurements. It is found that the Ni-W-P alloy showed a more superior corrosion resistance than the iron- base alloy with the smallest corrosion current and the most positive potential in3.5 wt% Na Cl solution, The corrosion potential of iron-based alloy was lower than that of Ni-W-P coating, when they galvanically coupled,iron-based alloy always acts as anode while the Ni-W-P alloy acts as cathode; The influence of microstructure and composition of the iron-base alloys on galvanic corrosion was discussed and the galvanic effect was in the following order:J55< N80< P110<35Cr Mo, The 35 Cr Moshows the smallest potential difference(272 mv) and the maximum galvanic effect(1.9406) when coupled Ni-W-P alloy, while J55 has a large potential difference(298mv) and minimum galvanic effect(1.2098).(2) The galvanic corrosion behavior between the Fe-Ni-W alloy and iron-based alloy of N80, P110, J55 and 35 Cr Mo in 3.5 wt% Na Cl aqueous solution was systematic studied by the weight loss test and electrochemical measurements. The experiments showed that the Fe-Ni-W alloy showed a more superior corrosion resistance than the iron- base alloy with the smallest corrosion current and the most positive potential in 3.5 wt% Na Cl solution, The corrosion potential of iron-based alloy was lower than that of Fe-Ni-W coating, when they galvanically coupled,iron-based alloy always acts as anode while the Fe-Ni-W alloy acts as cathode; the galvanic effect is small between the Fe-Ni-W coating and iron-based alloy due to a large number of micro-cell corrosion distracted the galvanic corrosion current formed in the Fe-Ni-W structure and the galvanic effect was in the following order:35Cr Mo >N80 > P110 > J55?(3) The galvanic corrosion behavior and corrosion mechanism between the Ni-P alloy, heat-treated Fe-Ni-W and Ni-W-P alloy and iron-based alloy of N80,P110,J55 and 35Cr Mo in 3.5 wt% Na Cl aqueous solution was systematic studied by the weight loss test and electrochemical measurements. The results showed that tungsten alloy coating exhibit different corrosion resistance under various heat treatment conditions in 3.5 wt% Na Cl aqueous solution which was ranked in order: Ni-W-P > Fe-Ni-W >electroless Ni-P. when they galvanically coupled,iron-based alloy always acts as anode while the the heat- treated tungsten alloy acts as cathode; the corrosion rate of iron base alloy is increased with galvanic effect, but due to the difference of the structure of the coating and the potential difference, it appeared different degree of galvanic corrosion, the galvanic corrosion was shown: Ni P > Ni WP(200 ?) > Ni WP(500 ?) > Fe Ni W(600 ?). |
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