电化学阻抗谱法研究热处理对低碳钢镍基合金涂层腐蚀行为的影响

EIS STUDY ON THE EFFECTS OF HEAT TREATMENT ON CORROSION BEHAVIOR OF NICKEL BASE ALLOY COATING ON LOW CARBON STEEL

采用超音速火焰喷涂(HVOF)方法在碳钢基体上制备了NiCrBSi喷涂层,对包覆样品进行900℃保温2h或10min热处理,利用电化学阻抗谱(EIS)研究了涂层在3.5%NaCl水溶液中的腐蚀失效过程和耐蚀性的变化规律.EIS图谱分析表明,喷态涂层抗介质渗透能力差,腐蚀20h后介质可渗达碳钢基体;900℃,2h保温热处理涂层腐蚀15 h后EIS谱发生明显变化,产生局部腐蚀;而900℃,10min处理涂层为均匀腐蚀,EIS谱形可长时间保持稳定.利用等效电路拟合,获取了涂层界面反应阻力(腐蚀抗力)随时间变化的关系,显示高温短时(10min)热处理涂层的界面反应阻力高且稳定,其耐蚀性和抗介质渗透能力远优于喷态涂层,但2h保温热处理涂层的耐蚀性比喷态涂层的差.利用组织结构分析解释了热处理影响涂层腐蚀行为的原因.

NiCrBSi alloy powders were sprayed on a low carbon steel substrate using high velocity oxy-fuel （HVOF） spraying technique and then the samples with coating were heat treated in air furnace for 2 h or 10 min at 900 ℃. The corrosion failure process and corrosion resistance of coatings in 3.5% NaCl aqueous solution were investigated by using electrochemical impedance spectroscopy （EIS）. The results show that the as-sprayed coating cannot resist the penetration of corrosive solution and after 20 h immersing the steel substrate was corroded; for the 2 h heat-treated sample local corrosion happened after 15 h immersing; for the 10 min treated sample its shape of EIS can hold stable for a long time and uniform corrosion happened. Relationships of corrosion resistance with time for assprayed and heat-treated coatings in 3.5%NaCl were obtained using equivalent circuits. The corrosion resistance of 10 min heat-treated coating and resistance to penetration of aqueous medium are far better than those of as-sprayed coating, but the corrosion resistance of 2 h heat-treated coatings is inferior to that of as-sprayed coating. The reasons why heat treatment can change the corrosion behavior of sprayed coating were discussed by analyzing microstructure.