A new method has been developed in which Zn/Ni double-coated films were electroplated onto steel substrates, and then irradiated, using a high powered YAG laser with kaleidoscope in lieu of a CO2 laser for surface modification to alloy the Zn/Ni films. The effects of film thickness and laser treatment conditions on the alloying of the Zn/Ni double-coated film were also investigated by EPMA and X-ray diffraction analysis. EPMA line analysis revealed that with laser irradiation under optimum conditions, a double-coated Zn/Ni film consisting of an overlying Zn film having an average thickness of 10μm and an underlying Ni film having an average thickness of 1.3μm formed a Zn-Ni alloy film in which Zn and Ni were uniformly distributed. X-ray diffraction analysis showed that the Zn-Ni alloy film was mainly composed of the Ni5Zn21 (γ-phase) structure.
Recently, TiN and TiC films formed by physical vapor deposition (PVD) and/or chemical vapor deposition (CVD) have been used to improve the wear resistance of cutting tools, dies, etc, but it has been claimed that films formed at different charges have different characteristics. Accordingly, this study attempts an evaluation by means of scratch tests and residual stress measurement. Failure of TiN and TiC films under scratch testing was detected by an AE sensor and a bending load cell, and scratch traces were observed by SEM. The surface residual stress of the films was measured by X-ray technique method. The results showed that scratch tests and residual stress measurement are means of evaluating difference in the characteristics of TiN and TiC films.
The probability of surface hardening by a plasma nitriding process was investigated for tentative Cu binary alloys containing Al, B, Cr, Fe, Mn, Si and Ti at nitriding temperatures of 773 to 1173K and nitriding times of up to 43.2ks in an N2+H2 mixed gas atmosphere at 800Pa. Surface hardening was observed in Cu-Ti and Cu-Mn binary alloys at nitriding temperatures of 1023 to 1173K. Maximum surface hardness was Hv 350∼500 for alloys containing Ti and Mn containing alloys of more than 5 and 10wt% respectively. Cu-Al, Cu-B, Cu-Cr, Cu-Fe and Cu-Si binary alloys, however, were not hardened. A nitrided layer was observed in alloys showing surface hardening as Cu-Ti and Cu-Mn binary alloys. From the results of EPMA and X-ray diffraction analysis, it was estimated that a nitriding layer was formed as a nitride compound layer consisting of TiN for Cu-Ti and Mn4N for Cu-Mn. Surface hardening is thus attributed to the formation of a nitrided compound layer on the surface of the specimen.
The authors investigated a method for electroless plating of nickel with no catalyzer, onto a substrate consisting of copper foil hot-pressed onto polyimide resin, using dimethylamine borane as the reducing reagent. When the substrate surface was oxidized before plating, reduction of the nickel ion was promoted. When solution temperature was high, the copper oxide film was reduced rapidly to copper and its surface morphology was similar to that of the original oxide surface. Accordingly the authors propose mechanism for the reduction of copper oxide film in an electroless nickel plating solution whereby: 1) If reduction of the oxide film is rapid, the film partially dissolves into the plating solution, and copper ions in the solution are reduced to copper metal and deposited. Undissolved copper oxide is directly reduced to copper in the film in parallel with the above reaction. 2) If reduction of the oxide film is slow, almost all the film dissolves into the plating solution, and the copper ions in solution are reduced to copper metal and deposited. 3) The copper metal that has been reduced and deposited is in the active state and a part of it promotes the reduction and deposition reactions of the nickel ion.
A study was been made on the effect of the addition of palladium chloride on the electrical contact properties of electroless nickel-palladium-phosphorus alloy films obtained using sodium hypophosphite as the reducing agent. The following results were obtained; 1) Stable baths were obtained by adding TDG and increasing the pH. 2) Film formation was controlled easily by changing the metallic ion of the baths. 3) The films were subjected to non-working and working life test (100V-0.5A) and were found to exhibit good electrical contact characteristics.
Composite coatings of graphite particles codeposited to an electroless Ni-B matrix obtained from the bath using dimethylamine borane (DMAB) as the reducing agent were produced, and the physical properties of the coatings were studied. It was possible to obtain composites containing up to 5.5wt% of graphite particles. The hardness of the coatings decreased with increasing graphite content. Ni-B-graphite composite coatings were found to have good self-lubricating properties and their contact resistance was as low as that of Ni-B coatings.
Electroless tin plating on nickel was investigated in baths using titanium trichloride as a reducing agent and sodium carbonate as the pH controller, and it was confirmed that bright, high-density coatings could be deposited rapidly at optimum conditions of pH 6.5∼7.5 and 50∼70°C. A typical bath contained 0.08M stannous chloride, 0.09M disodium EDTA, 0.10M NTA, 0.24M trisodium citrate, 0.04M titanium trichloride, and sodium carbonate for pH control. It was found that this process is also applicable to plating on copper and nonmetallic substrates, and is suitable for making tin films with far better solderability than those made using ammonium hydroxide as the pH controller.
The mechanism of the electrodeposition of metallic chromium on partially tin-coated steel sheet is discussed from the viewpoint of cathodic polarization behavior in the plating solution. The current density required for stable deposition of metallic chromium is higher on tin than on steel, doubtless due to the higher hydrogen overvoltage of tin. Lengthening of the period after tin plating and pre-electrolysis under the third peak region in the chromium plating bath are both effective in facilitating the formation of cathodic film and in accelerating the resultant deposition of metallic chromium.
Zn-based composite plated steel sheets are expected to exhibit better corrosion resistance than zinc- or zinc-alloy-plated steel due to the existence of dispersed particles. It is of importance, therefore, to clarify the codeposition mechanism of the dispersed particles in order to control the plating structure, and thereby control the corrosion resistance. A study was conducted on the electrodeposition behavior of Zn-Ni-SiO2 composite plated steel sheets that were electroplated from an electrolyte containing Zn ion, Ni ion and SiO2 colloid. It was found that the SiO2 content of the plated layers increased rapidly with an increase in the SiO2 concentration in the bath, showing that Guglielmi's two-step codeposition mechanism did not hold in this case. The cross-sectional structure of the plating layer was studied by grow discharge spectrometry (GDS) and transmission electron spectroscopy (TEM). It was found that Zn-7.4wt%Ni-1.6vol%SiO2 composite plating had a double-layered structure: an under layer consisting mainly of Zn-Ni alloy and an outer layer of segregated SiO2 thin film. Zn-12.1wt%Ni-20.5vol%SiO2 composite plating, on the other hand, had a laminar structure, consisting of aggregated layers of SiO2 and Zn-Ni alloy, and Zn-Ni alloy layers. It was concluded that these codeposition behaviors depended on the peculiar properties of SiO2, which adsorbs Ni ions in the bath selectively, and agglomerates at the cathode.
Heavy electrodeposition of silver from conventionally concentrated cyanide baths was studied in terms of bath composition, the range of appropriate current densities and cathodic polarization curves. It was found that the orientation indexes of silver deposits approached unity when the molarity ratio of KCN to AgCN was 5, and the appropriate range of potassium carbonate concentration varied with the molarity ratio of KCN to AgCN. Both potassium hydroxide and potassium carbonate must be added to baths for heavy silver electrodeposition. The appropriate range of potassium carbonate concentration increased with increases in the concentration of potassium hydroxide. Cathodic polarization also increased with increases in the concentration of potassium carbonate, but changed little with the addition of potassium hydroxide. The recommended conditions for heavy electrodeposition of silver in cyanide solutions with conventional concentration are AgCN: 40g/L, KCN: 98-107g/L, K2CO3: 10-70g/L, KOH: 10-40g/L at current density of not more than 1.8/dm2.
The effect of rinsing immediately after plating on the surface oxidation and solder wettability of bright nickel-plated surfaces has been studied. Nickel plating was carried out in a Watts bath with brightener by an electroplating technique, and the nickel-plated specimens were immediately dipped and rinsed in deionized water. The dissolved oxygen content in the deionized water was controlled by several methods such as aeration, exposure to open air and deaeration with nitrogen. Water temperature was varied from 5 to 100°C. The oxide films on the rinsed surfaces were examined by ellipsometry (ELL), X-ray photoelectron spectroscopy (XPS), and reflection high-energy electron diffraction (RHEED). The thickest oxide film was observed near 80°C with rinsing within 5 minutes. The amount of dissolved oxygen did not significantly affect oxide film thickness below 80°C. The surface oxide film was composed mainly of Ni2O3, its structure being controlled by water temperature. Oxide structure changed from amorphous to crystalline at about 40°C. Both the thickness and structure of the oxide films were found to be important factors for controlling the solder wettability of bright nickel-plated surfaces, and amorphous structure played a particularly decisive role in improving solder wettability. Rinsing in water containing ethyl alcohol dramatically improved solder wettability.
Corrosive wear between a mild steel coated with TiN and an uncoated mild steel was investigated in NaCl solution. The mass loss of uncoated mild steel in abrasion tests was higher than that of the coated mild steel at both stator and rotor position, due to mechanical abrasion against the harder TiN film, and to galvanic corrosion by contact with the TiN film of nobler potential. The attack at defects in the TiN film was weaker compared with the case where two mild steels coated with TiN were in contact. This is ascribed to the decrease in galvanic current by dispersion to an opposite mild steel, and to the coverage of the defects in the TiN film with wear debris or corrosion products.
The wide use of organic solvents, in recent years, has given new importance to the study of pitting corrosion of stainless steel in organic solutions, but reports on pitting corrosion behavior in ethanolic solutions are few and far between. This paper thus reports on a technique using a potentiostat to investigate the pitting corrosion behavior of SUS 304 stainless steel in HCl/ethanol and NaCl/ethanol aqueous solutions. The experimental results obtained are summerized as follows: 1. The pitting potential shifted to the high side with increases in scanning rate. 2. The pitting potential shifted to the low side with increases in the mole concentration of hydrochloric acid and NaCl. 3. The pitting potential shifted to the high side with increases in the percentage concentration of ethanol. 4. Ethyl ion in ethanol served as a kind of organic inhibitor of pitting corrosion within the limits of the present study.