《Table 3 Electrochemical corrosion characteristics data》

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《电子束熔覆WC-CoCr涂层的表面结构及耐磨性研究（英文）》

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As illustrated in Fig.10 and Table 3，the corrosion potential of untreated WC-CoCr coating is-0.702 V and the corrosion potential is-0.472 V after electron beam treatment.The corrosion potential moved forward obviously.The corrosion current density of the untreated WC-CoCr coating is 1.735×10-5 A/cm2，and that after electron beam cladding is only 2.624×10-6 A/cm2，which is reduced by an order of magnitude.It shows that the corrosion resistance of WC-CoCr ceramic coating is greatly improved by electron beam cladding.The corrosion current density of Inconel617alloy in 3.5%NaCl solution is 7.153×10-6 A/cm2 which is larger than that of the cladding layer，but their difference is little.It shows that the corrosion resistance of cladding is slightly better than that of Inconel617 alloy.The reason is that the WC-CoCr coating itself contains Cr element with excellent corrosion resistance and during the corrosion process，a small amount of chromium was added to the CoCr binder phase to form a chromium oxide passive film which can avoid the micro galvanic corrosion between the WC particles and the bonding phase.After the electron beam treatment，the addition of Ni and Mo elements with good corrosion resistance and the homogeneous distribution of Cr rich phases in the matrix are also the main reason for the increase of corrosion resistance of cladding layer.The performance of the corrosion depends largely on the elements of the material itself and on the composition of the elements[24].Some elements（such as Co，Cr，Mn，Al，etc）can improve the corrosion resistance of the material because they react with the corrosion elements to produce a dense passive film.Inconel617 alloy has higher corrosion resistance because it contains higher concentrations of Co，Cr and other elements which can improve corrosion resistance.WC-CoCr coating has a certain degree of corrosion resistance，but content of corrosion resisting elements is lower than that of Inconel617 alloy.However，after high energy electron beam treatment，the ion exchange between coating and substrate is achieved to improve the corrosion resistance of coating while the ion exchange between coating and substrate for the WC-CoCr coatings does not be achieved in the process of HVOF.Moreover，the molecular structure of the coatings is not changed by HVOF spraying and there is still a gap in the powder coating.The presence of gaps do not prevent the entry of corrosive elements.Therefore，the corrosion rate of the as-sprayed WC-CoCr coating is the highest.