超音速火焰喷涂WC-10Co4Cr涂层在NaCl溶液中的耐腐蚀性能

Corrosion-resistance of WC-10Co4Cr HVOF coating in NaCl solution

采用超音速火焰喷涂法(HVOF)制备高致密度的WC-10Co4Cr涂层。采用扫描电镜(SEM)、X线衍射(XRD)分析涂层的微观结构和物相变化,通过电化学极化测试和中性盐雾腐蚀试验研究HVOF WC-10Co4Cr涂层的抗腐蚀性能,并与不锈钢、电镀硬铬的性能进行对比。研究结果表明:采用这2种方法测得在NaCl溶液中各材料抗腐蚀性能由大到小顺序均为WC-10Co4Cr,电镀硬铬,不锈钢。电化学极化测试显示在3.5%NaCl溶液中WC-10Co4Cr涂层的腐蚀速率0.004 mm/a,为电镀硬铬的1/5。在35℃,5%NaCl溶液中盐雾腐蚀144 h后WC-10Co4Cr涂层仍保持良好的金属光泽,没有腐蚀痕迹。由于采用航空煤油液体燃料,喷涂过程中脱碳少,且涂层孔隙率极低(0.8%)、孔隙均匀分布,都使得Cl-不易穿透WC-10Co4Cr涂层形成微观腐蚀电池;Cr的添加促使形成耐蚀性更好的钴铬合金黏结相,能更有效地抑制黏结相在腐蚀介质中的溶解从而提高涂层耐蚀性。

A high density WC-10Co4 Cr coating was prepared by high velocity oxy-fuel（HVOF）. The microstructure and phase transformation were studied by scanning electron microscope（SEM） and X-ray diffraction（XRD）. The corrosion-resistance of the coating was investigated by electrochemical polarization test and neutral salt spray test, which was compared with that of stainless steel and electroplating hard chromium. The results show that WC-10Co4 Cr has the best corrosion-resistance, followed by electroplating hard chromium, and stainless steel the worst. The electrochemical polarization test indicates that, in 3.5%NaCl solution, the corrosion rate reaches 0.004 mm/a, which is one fifth of that of electroplating hard chromium. After immersing in 5%NaCl salt spray at 35 ℃ for 144 h, the coating still harbors metallic luster, and lays no corrosion stain. The extremely low porosity of WC-10Co4 Cr HVOF coating（porosity of 0.8%）,uniform distribution of pores and less decarburization during HVOF jointly contribute to nearly no penetration of Cl-, and further no formation of micro-corrosion cells. Co-Cr binding phase with better corrosion resistance is formed by adding Cr which reversely inhibits dissolution of the coating in corrosive media more effectively, leading to its optimal corrosion resistance.