电沉积nano-Al_2O_3/Ni+Co梯度复合镀层

nano-Al_2O_3/Ni+Co gradient composite coating by electrodeposition

采用电沉积方法以灰铸铁为基体制备了金属与纳米陶瓷复合镀层,基质金属为镍钴,第二相纳米陶瓷颗粒选用Al2O3。通过表面形态观察可知,由于纳米颗粒的高活性表面为沉积过程提供了大量的核心,使得复合镀层较金属镍钴镀层组织致密,晶粒细小。线扫描成分分析表明:镀层中纳米颗粒含量呈梯度分布。对其显微硬度进行测量,结果显示:复合镀层显微硬度由表层到里层呈梯度分布。耐磨性试验表明:复合镀层中Al2O3纳米颗粒产生的弥散强化效应和晶粒细化效应使复合镀层耐磨性显著优于纯镍钴镀层。对复合镀层和纯镍钴镀层磨损形貌的观察分析表明:复合镀层磨损表面出现沿摩擦副运动方向的犁沟,而纯镍钴镀层磨损表面呈现大片剥落,磨损机制为黏着磨损。

The metal and nano-ceramic nanocomposite coatings were prepared on gray cast iron surface by electrodeposition method.The nickel and cobalt were used as metal matrix,and the nano-Al2O3 was chosen as secondphase particulates.To avoid bad interface bonding and stress distribution,the gradient composite coating was prepared.Due to the high actively surface of nanoparticles provides an amount of nucleus the morphology of composite coatings was flatter and microstructure was denser than pure nickel and cobalt coatings.The result of line scan content indicated that nano-Al2O3 content distributed gradient.The measure data of microhardness indicated that the microhardness changed in gradient from outer layer to inter layer in coating.The wear experiments indicated that wear-resistance of the composite coating was well than pure nickel cobalt coating evidently.The reason was that nano-Al2O3 caused dispersive strengthening and grain refining.The wear morphologies of composite coating and pure nickel cobalt coating were observed.The results indicate that the composite coating abrasive grooves could be found alongside some cracks which were parallel to the sliding direction,severe plastic deformation could be observed on pure nickel cobalt coating wear surface and the wear mechism was ahension wear.