WC-Co合金在不同介质中的电化学腐蚀行为与腐蚀机理研究

Electrochemical Corrosion Behaviors and Corrosion Mechanism of WC-Co Cemented Carbide in Different Aggressive Mediums

研究了WC-10%Co合金在Na OH(p H=13)、Na2SO4(p H=7)以及H2SO4(p H=1)等3种介质中的电化学腐蚀行为。采用电化学阻抗谱(EIS)和动电位极化曲线2种方法研究合金的耐腐蚀性能,通过传质电阻和自腐蚀电流密度2个动力学参数对合金的耐腐蚀性能进行对比。通过合金腐蚀表面扫描电镜形貌观察和表面腐蚀产物的X射线光电子能谱元素价态分析,结合EIS对应的等效电路图对腐蚀机理进行研究。结果表明,Na OH介质对合金的腐蚀性最弱;H2SO4介质的腐蚀性最强,合金表层的Co全部产生了活化溶解;在3种介质中合金腐蚀的等效电路和腐蚀机理各不相同,在H2SO4介质中,合金的动电位极化曲线中出现了伪钝化现象,腐蚀机理的复杂程度排序如下:Na2SO4>H2SO4>Na OH。

The electrochemical corrosion behaviors of WC-10% Co cemented carbide were investigated in the electrolytes of NaOH （pH = 13）, Na2SO4 （pH = 7） and H2SO4 （pH = 1）, respectively. Potentiodynamic polarization curve and electrochemical impedance spectroscopy （EIS） were used to survey the electrochemical behavior. Two kinetic parameters i. e. charge transfer resistance, corrosion current density were used to describe the corrosion resistance. Scanning electron microscope and X-ray photoelectro spectroscopy were used to characterize the corrosion surface and the surface chemical state, in comparison with the EIS equivalent circuits, the corrosion mechanisms were investigated. The results show that the alloy exhibits the best corrosion resistance in NaOH. Nevertheless, the alloy performs the worst corrosion resistance in H2SO4 in which the Co binder phase on the surface is totally oxidized and dissolved. Additionally, the EIS equivalent circuits corresponding to the three electrolytes and hence the corresponding corrosion mechanisms are different from each other. A pseudo passivation phenomenon was observed in H2SO4 electrolyte. The following ordering of the corrosion mechanisms according to the complexity was found： Na2SO4 〉 H2SO4 〉 NaOH.