Basic Research On Deposit Morphology Control Technologies In Jet Electrodeposition By Smoothing, Multicomponenting And Interlacing

Jet electrodeposition (JED) has the good properties of large applicable current density, highcurrent efficiency, refined grains, compact deposited layers and so on. It is able to accelerate thedeposition speed by tens or up to hundreds of times which provides a new method for preparation ofnanocrystalline pure metals, alloys and composite deposits. But, the instability of crystallization underhigh current density would easily create defects of accumulated burls or dendrites on the depositsurfaces, which will seriously aggravate surfaces smoothness. It has already become the bottleneck inthe development of the technology. Morphology control is one important content during thepreparation procedure of materials. In this paper, a new method of deposit morphology control by aspecial process and guided flow fields is presented which can solve the long-standing problems andexplore the applications of JED. The mechanical grinding is introduced into JED, so that a newgrinding JED technology is developed. This technology can be used to change growing morphology,effectively inhibit the buildup of accumulated burls or dendrites. On this basis, the single jet unit istransited to a spatial jet units array, thus a novel "multicomponent arrayed jet electrodeposition"technology is proposed for the first time. This technology is expected to handle the processcomplexity, costly equipment and other inconveniences in current nanomultilayer film preparationmethod. Meanwhile, a research is done on the mechanism and method of crystal morphology controlachieved by promoting the growth of dendrites and guiding flow fields. The main research of thepaper is as follows:1. A research into the behavior mechanism of jet electrodepositing metal Ni usingelectrochemical testing techniques is conducted, which includes: the kinetic procedure of JED isinvestigated using Tafel curves; the polarization characteristics on cathode is analyzed through linearscanning curves; different cathodic polarization types are determined using electrochemical cyclicvoltammetry technology, etc. Test results indicate that implementing the high-speed jet willsignificantly reduce the concentration polarization, increase diffusion rate, reduce diffusion layerthickness, greatly raise limited current density and electrodeposition speed on the cathode, meanwhileenable great electrochemical polarization, increase the forming probability of crystal nuclei, andeventually help acquire better refined grain deposited layers with good quality. However, theinstability during crystallization under high current density in JED will speed up the evolution or propagation of the surface bulges. Moreover, under the relatively high exchange rate of electrolyte inJED, once the bulges are formed, they will grow at a large speed, then deteriorate surface flatness, andconsequently cause the deposition procedure to halt.2. An equipment system is developed for the research on grinding JED, multicomponent arrayedJED and controllable growing of the crystal, meanwhile feasible operation method and process floware designed and implemented. The system consists of machine tool, power source control system,electrolyte temperature control system, electrolyte jet and circulation system, step motor controlsystem, and deposition units for grinding JED or multicomponent arrayed JED. Step motor controlsystem consists of industrial computer, control software, servo drive, etc. The main function of thesesections is to control the motion trail of the nozzle and cathode.3. Influence factors (like current density, cathodic rotation speed, pulse ratio and frequency, etc.)on microstructure (surface morphology, texture, grain size), microhardness and anticorrosive propertyof the deposited Ni layers are researched and analyzed, and compared with Ni layers prepared bytraditional JED method. Investigation and property tests through SEM, contourgraph, XRD and TEMare carried out, and it is found that consecutive grinding and impact of hard particles brings obviousbenefits for burl trimming, making macroscopic surface relatively flat and smooth throughout thedeposition process, and they can also refine grains, affect the crystal growing, remarkably changemicrostructure and property of the deposited layers. Microhardness and anticorrosive property of thelayers have increased significantly. Magnetic property has been changed in that coercive force andremanence ratio are much greater. Meanwhile, with the application of pulse JED, grains areenormously refined, as well as the structure and property of the deposition layers are furtherimproved.4. Cu/Ni nanomultilayer films are successfully prepared in different process conditions usingmulticomponent arrayed JED, and the organization structure and mechanical properties are researched.SEM, XRD are used to characterize the periodic structure of the films, and to analyze the relationshipbetween interfacial structures of the films and the mechanical, anticorrosive property. Test resultsshow that the application of multicomponent arrayed JED suggests an easier method to design andprepare nanomultilayer films that can be of two or more components or alternately shifted structures,and in the meantime, make precise regulation and control to the components, modulation wavelengthsand cycle numbers.5. Mechanism and test research of the crystal morphology control using JED is achieved. The fractal theory is introduced to JED to investigate on the two dimensional dendrite growing procedure.In the meantime, theoretical analysis is made to investigate the flow field around the cathode in JED,mechanism of the crystal controllable growing is discussed. The controllability of growingmorphology of the dendrite is explored by regulating specific process parameters such as swingingtimes, swinging step lengths, etc, and porous metal structures of different morphology aresuccessfully prepared.