摘 要 电沉积复合镀是一种新兴的复合表面技术，它在电镀溶液中加入不溶性固体颗粒，并使其与基质金属在阴极上共沉积，形成具有优异性能的新型镀层，这种电沉积技术正逐渐成为研究焦点。本文在直流、单脉冲两种电流方式下，选取WC颗粒为增强相，钴为镀层基质金属，在W18Cr4V基体上制备Co-WC复合镀层。研究了镀液中WC颗粒的添加量、电流密度、搅拌速率、脉冲占空比、脉冲频率等参数与复合镀层的性能之间的关系，确定了电沉积Co-WC复合镀层的最佳工艺参数；利用光学显微镜、扫描电镜(SEM)、能谱仪(EDS)和X-ray衍射仪(XRD)等手段对复合镀层的截面形貌、化学成分和相结构进行了观察和分析。结果表明， WC颗粒均匀地分布在Co基质镀层内，复合镀层与基体界面清晰，且结合紧密；整个复合镀层平整均匀，厚度120μm左右；镀态下复合镀层均为晶态结构。当镀液中WC颗粒添加量为35g/L时，直流电沉积复合镀层颗粒复合量和镀速均达到最大，分别为17.4wt.%和56.3μm/h；而采用脉冲电沉积时，当占空比为50%，频率为500Hz时，镀层颗粒复含量和镀速分别为18.78wt.%和60.7μm/h；当稀土CeO2添加量为6g/L时，复合镀层颗粒复合量和沉积速率为19.9wt.%和78.2μm/h；同时研究还得出：WC颗粒的加入能显著提高复合镀层的显微硬度和耐磨性，但是降低了复合镀层的耐蚀性能。 用直流和脉冲电沉积技术分别制备了Co-WC复合镀层。研究结果表明，与直流镀层表面形貌相比，脉冲电沉积制备的复合镀层组织得到明显细化，晶粒尺寸减小，大小均匀，堆积更为紧密。探讨了不同电沉积方式对镀层沉积和生长过程的影响。结果表明，不同的电沉积方式并未使Co-WC复合镀层的晶体择优取向发生变化，脉冲电沉积使晶粒细化。直流电沉积时，基质金属的沉积连续进行，粒子在电极表面不间断的嵌入镀层，脉冲电沉积由于脉冲间歇存在使具有较大体积的粒子脱附重新回到溶液中，因此镀层中复合粒子尺寸小且均匀。脉冲电沉积得到的镀层晶粒细化，说明脉冲沉积方式阻碍了复合镀层中晶粒的长大，提高了电沉积过程中晶核的形成速率。 在直流电沉积下，研究了稀土CeO2和LaCl3对复合镀层微观组织、显微硬度及摩擦磨损性能的影响。研究结果表明，添加适量稀土提高Co-WC复合镀层中WC颗粒的沉积量，使WC颗粒在镀层中的分布更加均匀；CeO2添加量为6g/L时，复合镀层平均显微硬度比未添加CeO2时提高15.68%；而添加0.2g/L稀土LaCl3时，复合镀层平均显微硬度比未添加LaCl3时提高13.47%。摩擦磨损试验结果表明，稀土能改善复合镀层的干摩擦特性，有效防止镀层片状脱落，对镀层耐磨性有明显改善作用，CeO2添加量为6g/L时，复合镀层磨痕轻且窄，比未添加CeO2的磨损量减少了70%。在400℃高温下研究复合镀层的摩擦磨损性能得出，无论是直流还是脉冲电沉积所制备的复合镀层的磨损量较室温低，说明在高温400℃下Co-WC复合镀层的耐磨性提高。

ABSTRACT Composite electroplating is a sort of burgeoning composite surface technology which is adding particles into electrolyte or plate fluid, depositting the partials to the based metal bounding to cathode, and creating a new type of coating with superior properties. This technique is gradually becoming the plating research centre. In this paper, WC was chosen as reinforced phase and Co was chosen as based metal and Co-WC composite coatings were deposited on W18Cr4V substrates with direct current and pulse technologies. The connection among properties of composite coating and WC concentration in bath, stirring rate, current density, pulse duty cycle and pulse frequency were studied. The optimal parameters of electrodeposited Co-WC composite coatings were confirmed. The cross-sectional micrographs of the composite coatings were observed by optical microscope and scanning electron microscopy (SEM).The chemical composition and phase structure of composite coatings were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD).The results demonstrated that a relatively uniform concentration of WC particles disperse Co based mental, and the continuous and uniform composite coatings which show a clear bounding between composite coating and based metal with about 120μm of thickness indicate tight adhesion to substrate. The deposited structure of Co-WC composite coatings was crystalline. When the WC concentration in solution ascend to 35g/L, particles content in coating and deposition rate of DC composite coating reached the maximum, 17.4wt.% and 56.3μm/h, respectively. When the duty cycle was 50%, frequency was 500Hz, particles content in coating and deposition rate reached 18.78wt% and 60.7μm/h, respectively with using pulsed electrodeposition. When the Re (CeO2) concentration in solution ascend to 6g/L, particles content in coating and deposition rate were 19.9wt% and 78.2μm/h, respectively. Meanwhile, the study showed that the presence of WC particles can significantly enhance micro-hardness and wear resistance performances of composite coating. However, the corrosion resistance of the composite coating decreased. The Co-WC composite coatings were prepared by DC and pulsed electrodeposition respectively.The microstructure of the coating surface were observed by the scanning electron microscopy (SEM).The results revealed that the microstructure of the coating prepared by pulsed electrodeposition got better refinement, the grain size was decreased, the crystal size was uniform, and the accumulation was relatively tight compared with the surface Morphologies of DC plating. The microcosmic crystal-structure of the coating was analysed by XRD and the effect of the different deposition ways on the coating deposition and growth were studied. The results showed that the preferred orientation of the Co-WC composite coatings didn't change by different deposition methods, the grain refined, and lattice constant has increased, and crystal lattice distortion increase, making diffraction peaks of the coating composition reduce.The matrix metal deposited continuously, the particles embedded coating on the electrode surface uninterruptedly which prepared by DC electrodeposition. when prepared by pulsed electrodeposition, the size of the composite particles decreased in the coating as the larger-volume particles were desorbed and return to the solution owing to the off-time.The grain prepared by pulsed electrodeposition refined which demonstrated that the pulse deposition prevented the growth of grain and develop nucleation rate in deposition process. The influences of microstructure, microhardness, tribological properties which RE CeO2 and LaCl3 have effected on composite coating with direct current electrode -position were studied. The result shows that WC will distribute more homogeneous in coating if appropriate RE were added to promote WC deposition. The average microhardness of composite coating will be enhanced 15.68% with 6g/L CeO2 than the one without CeO2.Meanwhile, The average microhardness of composite coating will be enhanced 13.47% with 0.2g/L LaCl3 than the one without LaCl3. The result of friction-wear test shows that RE can improve the dry friction feature, prevent from sheet drop of coating efficiently, improved wear resistance of coating obviously. Grinding cracks of composite coating were slight and narrow and abrasion loss was reduced by 70% when 6g/L CeO2 were added. The friction and wearing properties of the composite coating under 400℃ shows that abrasion loss in high-temperature is reduced compared with room temperature with no matter direct current or pulsed electrodeposition. It demonstrates that wear resistance of Co-WC composite coating is improved under 400℃.