Papers by Author: Hui Fan

Abstract: Jet electrodeposition process is a very promising method in fabricating metal matrix composites reinforced with ceramic particles. In use of this method, insoluble particles suspended in an electrolytic bath are impinged onto and embedded in a growing metal layer. This paper is focused on the investigations of the copper matrix nanocomposite coatings with hard Al2O3 nanoparticles, electrochemically deposited from jet-circulated baths on 304 stainless steel substrate. The Cu-Al2O3 composite coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The effects of electrolyte jet velocity, current density, addition amount of Al2O3 in the electrolyte were analyzed on the microstructure change, surface morphology change as well as codeposited content of Al2O3 particles in the composite coating. It was found that increasing content of Al2O3 particles in electrolyte may improve composite coating surface morphology and increase the practical current density by exerting impingement effect on the cathode deposit surface, till excessive Al2O3 e.g.20g/L particles was added. Besides, appropriate amount of nanoparticles in the electrolyte also could offer grain refinement by providing nanocrystalline sized between 30~60 nm with current density in the range of 100~500 A/dm2.

Abstract: Jet electrodeposition is one of electrochemical machining methods, which is able to increase cathodic current density, therefore having high deposition rate, good locality and nanocrystalline structure. These advantages enable jet electro-deposition to integrate with rapid prototyping technology in an effort to achieve selective electro-deposition on the cathode surface. This paper combine both methods to prepare nanocrystalline copper parts. The equipment system is developed, which is mainly composed of computer control system, machine body, electrolyte circulation system, nozzle and its hoisting mechanism and other parts. Deposition rate, locality, deposit thickness distribution and forming accuracy are analyzed. A group of nanocrystalline copper parts having good shape and size precision have been prepared. Influencing factors on forming accuracy are analyzed.

Abstract: Laminated templates electroforming (LTE) is one kind of metal-parts directly forming technologies which are based on discrete/accumulation theory. This paper introduces the forming principle, equipment configuration and experimental studies. By using templates as auxiliary tool and jet electroforming as filling method, the current density of electroforming was significantly improved and a group of copper parts in specific shape were fabricated. Experimental results show that on-load voltage, nozzle diameter, spray distance, spray flow velocity have direct influence on processing speed and locality. A small diameter of nozzle and short spray distance helps to achieve a precise locality and good dimensional accuracy, after process parameters have been optimized.

Abstract: Deposit uniformity control is the key in laminated template electroforming and has direct influence on the parts shaping quality and processing cost. Accordingly, this research proposes a Assisted-Grinding pulse electro-deposition technology and designs the device and technology based on the principal. According to experimental method, a number of hard particles (ceramic beads) fill between the electrodes and are propelled by mandrels rotating movement to allow continuous impinging and grinding to the cathode surface, as an effort to instantaneously eliminate boundary effect that is caused by uneven current distribution. In comparison of the finish surface morphology and deposit thickness among the samples obtained respectively by traditional and new ways, the experimental results show that assistant friction could effectively remove the excess sediment and tumor along surface and provide a relatively flat layer with Ra 0.253μm. It shows particles-assisted-grinding has satisfactory practical values and is a novel exploration resolving the technical obstacle in electrodepositing.

Abstract: Laminated templates electro-deposition (LTE) is a new manufacturing technique aimed at a highly precise and low-cost fabrication of metallic structures through a number of planar template-patterned depositing. The ability to control deposit surface non-uniformity in each planar depositing has been proved a key to this technique. Correspondingly a 3D simulation for electrical field has been modeled using finite-element method in line with the real experimental conditions. The mapped contour of simulating proved the variedly distributed electrical field and basically match with experimental results. Three groups of LTE test by direct current, pulse and double-pulse current are introduced and assessed in term of their effect to improve uniformity. By comparison, pulse application, especially double-pulse offered a better deposit quality with optimized parameters including pulse width, frequency, working time and off time. A bulk of 10-15layers copper parts, section size 20mm×20mm and 4-6mm thick were produced using the modified parameters.

Abstract: Ni-SiC nano-composite coatings with various contents of SiC nano-particulates were prepared by means of the conventional electrodeposition in a nickel-plating bath containing SiC nano-particulates to be co-deposited. The surface morphology and structural constituent in the electrolyte layer were observed by SEM and EDS. The dependence of SiC nano-particulates amount in the nano-composite coatings was investigated in relation to the SiC concentration in bath. The effect of SiC nano-particulate incorporation content on micro-hardness as well as wear-resistance was studied too. The results showed that the nano-Ni-SiC plating layer had smooth and flat surface, uniform microstructure as well as higher micro-hardness and wear-resistance than pure Ni coating. The optimum experimental parameters were derived at condition of, addition of 6g/L SiC nano-particulates in the bath, 40°C temperature, current density of 4A/dm2 , and a stirring rate of 250rpm.

Abstract: Laminated templates electro-deposition (LTE) is a small-sized metallic-structure fabrication technique based on template-patterned depositing. Avoiding locally excessive electroplating at the template edge area has been proved crucial to this method. To improve deposition uniformity, auxiliary cathode and modulated double-pulse current were tried individually and assessed on their effects and efficiencies. By applying assisting cathode the deposition uniformity in plannar pattern depositing was significantly improved with an increased thickness ratio of edge to center for the plating sample. Pulse application, especially double-pulse was studied mainly on the proportion between anodic duty circle and cathodic duty circle. Through a group of optimized parameters, including current density ranging 8-10A/dm2, anodic and cathodic duty circle of respectively 80% and 30%, frequency 300HZ, a bulk of copper parts, section size 20×20mm and 4-7mm thick were produced with a well depositing quality.

Abstract: Laminated templates electro-deposition is an original manufacturing technology that is aimed at micro-scale metallic structures fabrication. Based on the discrete piling-up principal and electrodepositing method, it realizes a manufacturing simplification from the traditional machining to the repetition of template-assisted planar deposition in forming a three-dimensional complicated object. The ability to control the deposit surface nouniformity is a key to successful implementation for each planar depositing. Profile geometry and current configuration are alternated in experiment and thought as the major factors influencing deposit surface roughening. The results show that the surface of the deposits obtained by pulse electroforming has better performance in deposit thickness distribution and properties of the deposits. Optimized parameters have been obtained from the preliminary experiments in which 0.3millimeters-thick epoxy templates and 4~6A/dm2 current density were used at 40+ and a bulk of copper parts, section size 30mm×30mm and 7mm thick were produced and tested for their mechanical performance.