电沉积Cr-WO_3纳米复合镀层及其性能研究

Electrodepositing Cr-WO_3 Nano-composite Coating and Its Performance Evaluation

目的提高表面Cr镀层的耐腐蚀性能和热稳定性。方法将纳米WO_3颗粒充分分散于镀Cr液中。用直流电沉积的方法在低碳钢表面电沉积Cr-WO_3纳米复合镀层。通过金相显微镜、X射线衍射仪分别观察镀层表面微观形貌和测试镀层的物相结构。通过维氏硬度测试、极化曲线和电化学阻抗测试,分别评价Cr-WO_3纳米复合镀层的硬度和耐腐蚀性能。结果 Cr镀层和Cr-WO_3纳米复合镀层表面均呈现层片状的晶粒结构,Cr-WO_3纳米复合镀层的晶粒度更细小。在5%Na Cl溶液中进行电化学测试,相对于Cr镀层,Cr-WO_3纳米复合镀层的腐蚀电流密度下降至0.38μA/cm2,电化学阻抗值有所增大,其电化学活性相对Cr镀层更低,耐蚀性能更好。Cr镀层和Cr-WO_3复合镀层的硬度十分接近,纳米WO_3的加入并未明显提高其硬度值,但是能够抑制镀层在退火过程中裂纹的产生和扩展,减少镀层表面状态的变化。结论纳米WO_3颗粒的加入可以有效掺杂在镀层中,降低镀层的晶粒度。Cr-WO_3纳米复合镀层的电化学活性更低,耐蚀性性能更好。WO_3纳米的加入对未退火的镀层硬度的影响不显著,但能降低退火后镀层硬度降低的幅值,提高了镀层的热稳定性。

The work aims to improve corrosion resistance and thermal stability of chromium coating on low carbon steel. Nano WO3 particles were dispersed in chromium plating bath, and the Cr-WO3 nano composite coating was electrodeposited by direct-current electrodeposition from citric acid-sulfate bath. Then surface microtopography of the coating was observed by metallographic microscope and X-ray diffractometer （XRD）, and phase structure of the coating was tested. Hardness and corrosion resistance of the Cr-WO3 nano composite coating were evaluated by virtue of Vickers hardness test, polarization curve and electrochemical impedance test. Lamellar grain structure was present on the surfaces of Cr coating and Cr-WO3 nano composite coating, the grain size of Cr-WO3 nano composite coating was smaller than that of Cr coating. Electrochemical testing was performed in 5wt.% NaCl solution. Compared with the Cr coating, corrosion current density （Jcorr） of Cr-WO3 nano-composite coating decreased to 0.38 gA/cm^2, electrochemical impendence increased, electrochemical activity was lower and corrosion reistance was better. The hardness of Cr-WO3 nano-composite coating was close to that of Cr coating. Addition of Cr-WO3 did not contribute to higher hardness, but it could prevent presence and expansion of cracks on the coating during annealing, and reduce changes of coating surface states. Cr-WO3 particles could be mixed in the coating effectively to reduce grain size of the coating. The lower electrochemical activity of the Cr-WO3 nano-composite coating is, the better the corrosion resistance will be. WO3 nano has minor influence on the hardness of unannealed coating. However, it can reduce the value of amplitude of annealed coating and improve its thermal stability.