pH值对Cu-Co合金镀层结构及中温氧化行为的影响

Effects of pH Value on Structure and Medium-Temperature Oxidation Behavior of Cu-Co Alloy Coating

为探索适合用作铁素体不锈钢表面的保护涂层,在不同pH值条件下,通过电沉积法在SUS430铁素体不锈钢表面共沉积Cu-Co合金镀层,并在750℃下进行中温氧化试验,利用X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)等手段,分析镀层及氧化膜的形貌和组成,结合增重法研究Cu-Co合金镀层的中温抗氧化性能。结果表明:随着pH值的增加,镀层中Co元素的含量逐渐增大,Cu元素含量逐渐减小;在750℃中温氧化时,pH=6试样氧化速率最小;经400 h氧化后,基体表面的氧化物为Cr_2O_3和Fe_3O_4,pH=4镀层的氧化物主要为CuO,pH=5镀层的氧化物开始形成(Cu,Co)_3O_4尖晶石氧化物,pH=6镀层的氧化物中(Cu,Co)_3O_4和CuO成为主相;随着氧化时间的延长,pH=4,5镀层的氧化物晶粒缓慢长大,pH=6镀层的氧化物颗粒逐步细化;Cu-Co合金镀层氧化后的氧化层与SUS430钢的热匹配性较好,且镀层中Co含量较高时,其抗氧化性也较好,因此,pH=6镀液中获得的合金镀层适合用作铁素体不锈钢表面保护涂层。

In order to explore suitable protective coatings for ferritic stainless steel, Cu - Co alloy co - deposition coatings were prepared on the surface of SUS430 ferritie stainless steel by composite electrodeposition at different pH values. The medium-temperature oxidation resistance of Cu-Co alloy coatings was studied at 750℃. The microstructure and composition of Cu-Co alloy coatings were studied by X-ray diffractometer （XRD）, scanning electron microscopy （SEM） and energy spectrum analysis （EDS）. Results showed that with the increase of pH value, the content of Co in the coating gradually increased while the content of Cu decreased gradually. The oxidation rate at 750 ~C of the sample at pH = 6 was the lowest, and after the oxidation of 400 h the oxides on the substrate surface were Cr203 and Fe304. The oxides were mainly CuO at pH = 4, began to form （Cu, Co）3O4 spinel oxides at pH = 5, and became the main phase （Cu, Co）3O4 and CuO of the coating oxide at pH = 6. Besides, as the oxidation time was prolonged, the oxide grains grew slowly at pH = 4 and 5. At pH = 6 the particles of the coating were progressively refined. The thermal expansion coefficients of the Cu- Co alloy coating were matched well with those of SUS430, and when Co content was higher in the coating, the better oxidation resistance was obtained. Consequently, the alloy coating at pH = 6 was suitable as the ferritic stainless steel surface protective coating.