磁控溅射制备的Cr/CrN和Cr/CrN/CrAlN涂层耐腐蚀性能对比研究

目的比较Cr/CrN/CrAlN涂层和Cr/CrN交替涂层的耐腐蚀性能。方法利用电化学极化曲线、阻抗谱和中性盐雾试验进行测量,结合扫描电子显微镜(SEM)和原子力显微镜(AFM)表征微观形貌,分析两种涂层耐腐蚀性能的差异。同时,为研究涂层在服役中的损伤工况,分析了预制划痕对Cr/CrN/CrAlN涂层耐腐蚀性能的影响。结果Cr/CrN/CrAlN涂层的自腐蚀电流密度较Cr/CrN交替涂层和TC4基体低2个数量级,腐蚀速率较小。无损伤的Cr/CrN/CrAlN涂层的极化电阻Rp为868.7 kΩ·cm^2,预制1条损伤划痕涂层的极化电阻为792.0 kΩ·cm^2,而带有5条损伤划痕涂层的极化电阻Rp仅为77.2 kΩ·cm^2,减小至原始涂层的8%。Cr/CrN/CrAlN涂层经288 h连续盐雾腐蚀后增重仅为0.1 mg/cm^2,远小于CrN涂层和TC4基体,且增重速率趋于平缓。CrN涂层在连续盐雾腐蚀24 h后,腐蚀增重速率明显增加。结论由于Cr/CrN/CrAlN涂层结构增加了微裂纹和位错运动的界面阻塞,避免孔隙的连通,阻碍了腐蚀介质进入基体,因此涂层的耐腐蚀性能提高。对于表面预制划痕的Cr/CrN/CrAlN涂层,首先发生涂层的局部腐蚀,通过阴极极化加速后,腐蚀凹坑延伸到涂层/基体界面,加剧涂层的局部剥离。

Comparison of Corrosion Resistance of Cr/CrN and Cr/CrN/CrAlN Coatings Deposited by Magnetron Sputtering

The work aims to compare the corrosion resistance performance of Cr/CrN/CrAlN coating and Cr/CrN alternating coating.Electrochemical polarization curve,impedance spectrum and neutral salt spray test were used to analyze the difference in corrosion resistance of the two coatings by characterizing the microstructure with micro-morphology of scanning electron microscope(SEM)and atomic force microscopy(AFM).The effect of pre-scratching on the corrosion resistance of the coating was investigated to simulate the damage conditions of coatings during service.The self-corrosion current density of the Cr/CrN/CrAlN coating was 2 orders lower than that of the Cr/CrN alternating coating and the TC4 substrate and the corrosion rate was reduced.The polarization resistance Rp of the non-damaged Cr/CrN/CrAlN coating was 868.7 kΩ·cm^2,and that of coating with a scratch remained 792.0 kΩ·cm^2.However,the resistance Rp of the coating with 5 scratches was 77.2 kΩ·cm^2,which is reduced to about 8%of that in the original coating.After 288 h continuous salt spray corrosion,the weight gain per unit area of Cr/CrN/CrAlN coating was only 0.1 mg/cm^2,which was much smaller than that of Cr/CrN alternating coating and TC4 substrate,and the weight gain curve tended to become flat.The corrosion weight gain rate of the Cr/CrN coating increased significantly after continuous salt spray corrosion for 24 h,and the slope of the weight gain curve increased obviously.The Cr/CrN/CrAlN coating increases the interface clogging of microcracks and dislocation motion,which avoids the connection of the pores and prevents corrosion medium from entering the substrate,so the corrosion resistance is improved.For Cr/CrN/CrAlN coating with pre-scratched surface,local corrosion of the coating firstly occurs.After acceleration by cathodic polarization,the corrosion pit extends to the interface of coating/substrate,which exacerbates the partial peeling of the coating.