目的发展具有空间分辨的腐蚀电化学研究方法。方法用电沉积方法在铜基体上制备Ni和Ni-P涂层,应用扫描电镜和XRD检测涂层表面形貌和晶体结构,采用扫描电化学显微镜(SECM)研究Ni和Ni-P涂层在不同浓度Na Cl溶液中的失效行为,并结合COMSOL多物理场软件建立二维和三维模型,模拟量化活性点大小和反馈机制。结果低浓度Cl-对于纯Ni涂层具有活化作用,增加Cl-浓度会促进腐蚀发生。Ni-P合金涂层在低浓度Na Cl溶液中,短时间内保持良好的稳定性,浸泡6 h后,低P合金涂层出现典型的活性点和腐蚀产物,而高P合金涂层在浸泡24 h后出现腐蚀产物和活性区域。0.1 mol/L的Na Cl溶液促进低P合金涂层局部腐蚀的发生,而涂层在0.3 mol/L Na Cl溶液中则以发生均匀腐蚀为主。逼近曲线及其模拟结果表明,腐蚀产物对于Fc Me OH的电化学过程完全失活,而新鲜Cu表面对Fc Me OH氧化还原过程受扩散控制。三维模拟结果显示,低P合金涂层失效过程中活性点大小接近10μm。结论 Ni和Ni-P合金涂层的失效过程中活性点的形成、腐蚀产物的生成和累积过程与SECM面扫描图谱中正负反馈效应相关,Cl-促进腐蚀发生,其浓度影响腐蚀类型。COMSOL多物理场模拟明确反馈效应与探针和基底的距离有关,Ni-P涂层失效活性点大小在微米级。
In order to improve the corrosion resistance and microhardness of AZ91D magnesium alloy, TiN nanoparticles were addedto fabricate Ni-P-TiN composite coating by electrodeposition. The surface, cross-section morphology and composition wereexamined using SEM, EDS and XRD, and the corrosion resistance was checked by electrochemical technology. The results indicatethat TiN nanoparticles were doped successfully in the Ni-P matrix after a series of complex pretreatments including activation, zincimmersion and pre-electroplating, which enhances the stability of magnesium alloy in electrolyte and the adhesion betweenmagnesium alloy and composite coating. The microhardness of the Ni-P coating increases dramatically by adding TiN nanoparticlesand subsequent heat treatment. The corrosion experimental results indicate that the corrosion resistance of Ni-P-TiN compositecoating is much higher than that of uncoated AZ91D magnesium alloy and similar with Ni-P coating in short immersion time.However, TiN nanoparticles play a significant role in long-term corrosion resistance of composite coatings.
