直流与脉冲电沉积Ni-Cr合金镀层的结构及耐蚀性

用直流电沉积(DC)、脉冲电沉积(PC)技术在低碳钢表面制备Ni-Cr合金镀层,采用X射线衍射(XRD)、扫描电镜(SEM)、原子力显微镜(AFM)等方法,研究了电沉积方式对合金镀层晶粒结构和表面形貌的影响;用浸泡法和电化学极化法测试了合金镀层在3.5%(质量分数)Na Cl溶液中的耐蚀性。结果表明,电沉积方式对镀层结构和性能有较大影响:PC方式得到的合金镀层,其纳米晶尺寸更小(由45 nm减小为26 nm),镀层表面致密性更高;表现在性能上,与DC相比,PC合金镀层的显微硬度更大(由7000 MPa增加到8250 MPa),耐蚀性更好(自腐蚀电位由–0.624V正移到–0.477 V,腐蚀电流密度由1.911×10~(-4)A/cm~2减小到2.587×10~(-5) A/cm~2)。

Microstructure and corrosion-resistance performance of Ni-Cr alloy coatings by direct and pulse current electrodeposition

Ni-Cr alloy coatings were obtained on mild carbon steel surface by direct current (DC) and pulse current (PC) electrodeposition. X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) and atomic force microscope (AFM) were used to analyze the phase structure and surface morphology. The corrosion behaviors of Ni-Cr alloy coatings in the 3.5% (mass fraction) NaCl were investigated by soak method and electrochemical polarization method. The results show that microstructure and performance of the coatings were greatly affected by electrodeposition methods. The pulse electrodeposition can increase the amounts of new nuclei and reduce grain size, so the PC alloy coatings exhibit a relatively uniform and fine structure. The self-corrosion potential (Ecorr) of PC alloy coatings is increased from -0.624V to -0.477V and the corrosion current density (Icorr) is decreased from 1.911?0-4 A.cm-2 to 3.789?0-5 A.cm-2 compared to those of the DC alloy coatings. The PC alloy coatings have better corrosion resistance than DC alloy coatings.