镍基合金涂层包覆钢腐蚀失效过程的电化学阻抗谱研究

EIS STUDY OF THE CORROSION FAILURE PROCESS OF STEEL COATED BY NICKEL BASE ALLOY

采用超音速火焰喷涂(HVOF)方法在低碳钢表面制备NiCrBSi合金涂层,将包覆样品在真空下进行600℃热处理并保温2 h,利用电化学阻抗谱(EIS)研究镍基合金层在3.5％NaCl溶液中的腐蚀失效过程,提出了电极在腐蚀过程中的不同阻抗模型.涂层腐蚀初期为均匀腐蚀, EIS谱中存在明显的电感效应且随着时间的延长逐渐减弱并消失说明了孔蚀诱发的过程,模型为R(QR(RL)).随着腐蚀时间的延长,涂层上出现局部腐蚀,介质通过孔隙腐蚀孔内金属,模型为R(Q(R(QR))).孔蚀在涂层内的发展后期,因为闭塞电池作用使得介质在孔内的有限长度扩散过程影响显著,模型为R(Q(RO(QR))).腐蚀介质渗透通过涂层到达基体后,碳钢发生选择性腐蚀,模型为R(Q(R(QR))).按照上述模型分阶段对EIS数据进行拟合,获得了各电路参数随时间的变化关系,解释了电化学反应界面的变化特点.

The NiCrBSi alloy powder was sprayed to a steel substrate using high velocity oxy-fuel (HVOF) spraying technique and then the sample with coating was heat treated in vacuum for 2 h at 600 V. The corrosion failure process of the coating in 3.5%NaCl aqueous solution was investigated by using electrochemical impedance spectroscopy (EIS). The simulation and interpretation of EIS data with different models were carried out, and the relationships of the produced various variables with time were analyzed. The shrinkage phenomena in low frequency range of the measured impedance spectra can be well interpreted by the violent change in electrochemical parameters at the initiation stage of pitting corrosion, and the model at this stage is R(QR(RL)). At the propagation stage of pitting corrosion, the model is R(Q(R(QR))) initially, and then is R(Q(RO(QR))). Steel substrate will be preferentially corroded after the solution penetrated into the interface between coating and steel, and the model is R(Q(R(QR))).