Attempts have been made to improve the thermal and wear resistance of electroplated nickelsilicon carbide composite coatings. Coating methods have been investigated by adopting an up-flow bath system, and the coated surfaces have been examined by using scanning electron microscopy. The amount of co-deposited silicon carbide was reduced by increasing the electrolyte flow rate. Films with 2.5-4.0 wt% co-deposit of silicon carbide were obtained at a current density of 30A/dm2, in the bath containing 200g/l of dispersed silicon carbide with 100cm/sec of flow rate. Addition of 0.2g/l of phosphorous, e.g. phosphorous acid, hypophosphorous acid, or sodium phosphite, to the electrolyte provided the film with greater thermal resistance. In the application of this composite film to a cylinder bore of 2-stroke engine, it turned out that wear loss of this coating was approximately 60 percent of that of conventional cast iron sleeve cylinder. After more than 20, 000km test running, the wear loss of the cylinder bore was less than 2.5μm in depth, around the top end position of the piston. Both the protruded silicon carbide powders on the nickel matrix surface produced by electrolyticpolishing and the hard nickel matrix obtained by adding phosphorous compounds have thus made the improvement of wear resistance possible.
Magnetic properties of Permalloy films consisting of nickel and iron are influenced significantly by their compositions. It is necessary, therefore, to understand the relationship between the plating conditions and the resulting compositions. The conditions for obtaining Permalloy films of regular compositions from sulfamate solutions are discussed. It is concluded that the electroplating at relatively low ferrous ion concentrations and low current densities is most favorable.
The effects of the surface morphology of zinc-phenol resin composite coatings and of the surface area of the particles entrapped in the surfaces have been investigated for the adhesion of polyethylene or polyamide layer to the composite coatings. The bond strength was determined by using 180°peel test, while the fractured surfaces were examined by SEM. SEM observations of the fractured surfaces revealed that cohesive failure took place in polyethylene layer in the polyethylene and composite substrate system, but adhesive failure at the interface in the polyamide and composite substrate system. Bond strength of the composite coatings obtained at a current density of 5A/dm2 and having scale-like projections of zinc deposit was found to be greater than that of the coatings (30A/dm2). A maximum in peel strength was obtained with the coating the surface of which was covered with the particles to the extent of 17-25%. These can be explained in terms of an increase in real contact area between the polymer layers and the substrates due to increased roughness zinc surface, and also of the presence of phenol resin particles on the composite film surfaces.
Ni-P films electrodeposited on an aluminium alloy substrate have been investigated for the purpose of developing a plated magnetic recording disk. A plating equipment was designed to keep the plating solution thoroughly clean and to heighten the effect of air agitation at the plating surfaces. In addition, a cathodic shielding technique was employed to secure uniformity in film thickness and phosphorous content. The films obtained by using these techniques showed high Vickers hardness (Hv=600-700), low residual stress (σ=1.4-5.4kg/mm2), and high non-magnetic stability (activation energy E=1.78eV, relaxation time T=103 years at 50°C), which are suitable for the substrate of the plated magnetic disk. Thickness deviation was within 5% irrespective of the film thickness. This uniformity developed a mechanical finishing efficiency of the plating surface. Signal errors under the read-write operation were avoided by using the non-defect plated substrate. The electrodeposited Ni-P films thus can be practically utilized for the plated magnetic recording disk and surely have an economical merit of high recording density.
Electrodeposition of Ni-Al2O3 and Ni-ZrO2 from a Watts nickel bath has been studied to determine the factors affecting the codeposition of the oxide particles into nickel matrix. The amount of the oxide particles codeposited into the nickel deposits was found to increase linearly with decreasing pH of the plating bath under the constant current density. Higher content of the oxide particles in the deposits was observed at lower current densities. The surface appearance and hardness of the composite coatings as well as the contents of the oxide particles were affected by the organic cations such as fluorescent dye or crystal violet. It was confirmed that nickel ions, protons, and/or organic cations are adsorbed on the oxide particles bringing about the positive surface charge, and thus they promote the entrapment of the oxide particles into the nickel deposits. Codeposition of the oxide particles into nickel matrix can be explained by the hydrodynamic transport of the particles and the field-assisted electrosorption of the oxide particles to the cathode, and finally by the electrochemical entrapment of the particles into the growing crystal.
As part of the investigation of electroforming of ceramic dispersed metal matrix composites, the electrodeposition of Ni-Al2O3 composites on rotating cylinder cathode in alumina dispersed Wattstype electrolyte has been studied. Previous investigations have dealt almost exclusively with stationary cathode. In this study, a seamless tube of 1mm thick and 10mm inner diameter was electroformed using a copper-plated plastic cylinder cathode. A new relationship between the volume percent of codeposited alumina (α*), which was determined by the apparent density measurement, and the alumina content in bath (C) was observed. For the data obtained with stationary cathode, the Langmuir plot of C/α* vs. C gives a straight line. For those with rotating cathode, however, this plot is not successful but a direct plot of α*vs. C shows an S-shaped curve. As the revolution rate of the cathode increases, both the amount and the size of dispersed alumina in the compositedecreases.