沉积参数对阴极等离子电解沉积Ni涂层的影响

Ni Coating Fabricated by Cathodic Plasma Electrolytic Deposition withDifferent Deposition Parameters

采用阴极等离子电解沉积(CPED)技术制备了金属Ni涂层,研究了单次沉积和循环沉积两种模式下的沉积参数对Ni涂层沉积过程的影响,讨论了CPED制备Ni涂层的沉积机制。结果表明,采用单次沉积模式时,在沉积电压为100~110 V范围内,适当的增加沉积电压有助于平滑涂层的表面形貌;而沉积电压超过110 V会加剧等离子放电的强度和密度,引起孔洞和缺陷;随着沉积时间的增加,涂层生长经历了形核-熔融两个交替过程。涂层厚度先增加后趋于稳定,沉积时间为10 min时,涂层厚度最大(10.77μm)。采用循环沉积模式时,随着提拉速度的增加,涂层的表面粗糙度呈先减小后增加的趋势。在900μm·s^(-1)的提拉速度下制备的涂层具有最平坦和最均匀的表面(表面粗糙度(S_(a))=2.11μm,最大高度(S_(z))=21.13μm);浸没时间的增加导致涂层表面的熔融态形貌特征更明显。与浸没时间为10 s的涂层相比,浸没30 s所得涂层的S_(z)和S_(a)分别降低了40.7%和52.9%,涂层厚度增加了18%以上;随着沉积道次的增加,涂层的表面粗糙度和厚度不断增大。与沉积5道次得到的涂层相比,沉积20道次所得涂层的S_(a)和S_(z)分别增加了约5.5倍和2.8倍,涂层厚度可达24.24μm,但致密性较差,涂层中存在直径约为2μm的孔隙。

Ni coating has engendered considerable interest as an attractive candidate for functional coating,which has good oxida⁃tion,excellent corrosion,and wear resistance.Ni coatings are widely used in aeronautical coatings,biomedical devices,and marine engineering.Thermal spraying,hot dip,and other methods have been used to manufacture Ni coatings.Those technical means are complicated in process,strict in equipment requirements,and high in cost,which restricts the development and application of Ni coat⁃ing.Cathodic plasma electrolytic deposition(CPED)has attracted more and more attention in coating preparation and surface modifica⁃tion in recent years due to the ability to produce effectively clean surfaces,good coating adhesion,high deposition rate,relatively sim⁃ple and environmentally friendly.The quality of CPED-prepared coatings is affected by various parameters,such as electrolyte parame⁃ters,treatment time,electrolyte temperature,and power supply parameters.To realize the controlled processing of CPED technology,it is necessary to deeply study the effect of these deposition parameters and optimize the coating preparation process.Pure Ni coatings were prepared using the cathodic plasma electrolytic deposition technique.The effects of deposition parameters on the deposition pro⁃cess of Ni coatings in both single deposition and cyclic deposition modes were systematically investigated using the field emission scan⁃ning electron microscope(FESEM),the energy dispersive spectrometer(EDS),and the laser confocal scanning microscopy(LCSM).In addition,the deposition mechanism of Ni coatings prepared by CPED was summarized and discussed.The results showed that in the single deposition mode,an appropriate increase in deposition voltage in the range of 100~110 V helped to smooth the surface morphol⁃ogy of the coatings.The arithmetic mean deviation(S_(a))and maximum height of profile(S_(z))of the coatings gradually decreased with the increase in voltage.With the increase of voltage,the diameter of spherical particles in Ni coatings decreased,which could be attribut⁃ed to the increase of the nucleation rate due to the shortening period of the bubble generation and collapse.When the voltage exceeded 110 V,the intensity and density of the plasma discharge were intensified,causing holes and defects.In the single deposition mode,the nodules morphology alternated with the flat melt morphology after more than 3 min of deposition time.The appearance of the two al⁃ternating morphologies could be attributed to the nodules induced a distortion of the local electric field,which became the dominant re⁃gion of the plasma discharge under the action of the tip discharge.Under the action of partial high-density plasma discharge,the nod⁃ule gradually melted with the appearance of typical melt morphology.With the increase of deposition time,the coating thickness first increased and then tended to stabilize.The coating thickness was maximum(~10μm)at a deposition time of 10 min.In addition,the coatings were flat and dense with good coverage when deposition time were less than 10 min.With deposition time over 10 min,the de⁃fects of the coatings became obvious,and even the substrate was exposed.In the cyclic deposition mode,when the lifting speed was 1200μm·s^(-1),the area of cathode instantaneous conduction was relatively large,and the establishment process of gas film was easily interfered with by large bubbles,which led to abnormal deposition.At a lifting speed of 600μm·s-1,the deposition time at the same point of the cathode was relatively long,which increased the possibility of forming dendritic morphology,thus affecting the uniformity of the coating.S_(z) and S_(a) of Ni coatings first decreased and then increased with the increase of the lifting speed.The coating prepared at a lifting speed of 900μm·s^(-1) had the flattest and most uniform surface(S_(a)=2.11μm,S_(z)=21.13μm)with a coating thickness of 5.62μm.An increase in the immersion time led to more pronounced melt state morphology and smoother coating surface in the cyclic depo⁃sition mode.Compared with the coating prepared at an immersion time of 10 s,S_(z) and S_(a) of the coatings obtained at 30 s decreased by 40.7%and 52.9%,respectively,while the coating thickness increased by over 18%.Increasing the depositions passes resulted in the preferential growth of the dendrites,which could be attributed to the vapor gaseous envelope periodically underwent build-up and change,and the tip discharge was significantly weaker than single long-time deposition.As the deposition passes increased,S_(z) and S_(a) continuously increased,and the porosity of the coating gradually increased,forming a three-dimensional porous rough morphology.Compared with the coating obtained by depositing 5 passes,S_(a) and S_(z) of the coating obtained by depositing 20 passes increased about 5.5 times and 2.8 times,respectively.There was no significant increase in the thickness of the dense zone by increasing the depositions passes,and the increase in coating thickness was almost entirely contributed by the growth of the dendritic loose zone.The thickness of the coating obtained at 20 deposition passes was up to 24.24μm,but the densification was poor,with pores of about 2μm in diameter between the dendrites.