TiN coatings with thicknesses of 4 to 6μm were deposited by the DC glow discharge method from mixed gases of TiCl4, N2, H2 and Ar at a total pressure of 4Torr onto M2 steel and pure iron at temperatures of from 405°C to 600°C. X-ray microanalysis and microvickers hardness measurement revealed a correlation between the composition and hardness of the coatings. The results obtained were as follows: 1) The hardness of the coatings deposited at 550°C and 600°C was more than Hv 2000, while that of coatings deposited below 550°C decreased with decreasing substrate temperature, dropping to Hv 300 at 405°C and 465°C. 2) The chlorine content in the coatings increased with decreasing substrate temperature below 550°C, and amounted to more than 30at. % at 405°C and 465°C. 3) The hardness of the coatings decreased with increasing chlorine content. 4) In coatings containing less than 10at. % chlorine, in which there was a compensative relation between nitrogen and chlorine content, both the titanium and the sum of the nitrogen and chlorine content were constant at 50at. %.
Using a rotating disk electrode, cathodic current-potential curves that were free from concentration over-voltage (ηc) were obtained. At potentials of -0.75∼-0.90V (SCE) on the cathodic polarization curves, the Tafel slope was 0.73 and the reaction order of gold ion was l. The following electrodeposition mechanism was inferred. Na3Au(SO3)2_??_3Na++Au(SO3)23-……(1) Au(SO3)23-_??_AuSO3-+SO32-……(2) AuSO3-+e_??_Au+SO32-……(3) That is to say, Eq. (3) is the rate determinig process in the deposition of gold.
Electrolyte composition and the plating conditions of aluminum plating from 1-butylpyridinium chloride-AlCl3 molten salt were investigated at room temperature. The following results were obtained, (1) Electrolyte density increased with greater AlCl3 content, but conductivity and viscosity decreased. (2) The deposition potential of Al from the electrolyte changed suddenly at 50mol % AlCl3 content, and this was attributed to the difference in reduction potential between AlCl4- and Al2Cl7- (3) The current density range in which an adhesive Al plating could be obtained became wider with greater AlCl3 content. In baths with 67mol% AlCl3, dense and adhesive Al plating was obtained at 2.0A/dm2. (4) In the case of pulse plating, a very dense Al deposit was obtained at a small number of duty cycles.
Ag-ZrB2 dispersion plating was carried out from Ag cyanide plating baths containing suspended ZrB2 particles. Such plating has such advantageous properties as high melting point, excellent hardness, high electrical conductivity and good corrosion- and oxidation resistance. Some properties of the composite surface were investigated. The content of the ZrB2 particles in the composite layer, which was obtained under the conditions of 5A/dm2, 1200rpm, 1.0g/25mL and room temperature, was about 6wt% by gravimetric analysis. The hardness Hv of the Ag-ZrB2 composite layers was ranged from 105 to 120, about 1.3∼1.5 times those for pure Ag plating layers. In abrasion tests using a tester of our own devising, erosion of surface layers was less than 10% for Ag-ZrB2 composite and 20% for pure Ag deposit after the same number of rotations of the rub head. Electrical contact resistance between the Cu substrate and the composite layers was not different from that between the Cu substrate and deposited Ag, and it was shown that contacts was ohmic. Some test pieces of the Cu substrate plated with Ag-ZrB2 were set in the contact points of relay switches and a 100-VAC, 50Hz, 60-W resistive load (incandescent light bulb) was switched on and off. After 5×105 switching cycles no change was detected in contact resistance and the change in surface roughness was very slight in spite of the heat of arc discharge. These facts indicate that the composite layer of Ag-ZrB2 has many of the advantages of ZrB2, and that surface so plated may be suitable for use as contact material for electronic devices.
This study has been conducted to elucidate the thermal interfacial reaction between dispersed 1μm WC particles and the Watts Ni matrix. The reaction was characterized by chemical analysis and ductility testing of the composite after 1h annealing at temperatures up to 1000°C, as well as by transmission electron microscopy of the extracted particles. A particle-matrix bonding reaction occurred at temperatures above 300°C, and the bonding strengthened increasingly at higher temperatures. The reaction was found to be comprised by the dissolution of tungsten at the particle surface into the matrix, and the formation of a graphite carbon film, which enveloped the WC particles. Thus the bond strength comes from the WC/Graphite/Ni interface. Once the graphite film had grown to a thickness of only about 70Å at the expense of the approximately 160Å-thick WC surface layer, it functioned as a reaction barrier inhibiting further progress in tungsten dissolution and thereby in the size decrease of the WC particles.
This study was conducted on the insoluble anode materials that are required to prevent the degradation of a citric acid-ammonia Ni-W alloy plating bath of pH 6, 70°C. Bath degradation occurs by anodic oxidation of citric acid. It accompanies the evolution of CO2 gas from the anode and leads to the formation of highly stressed brittle deposits. Anode materials such as Pt, Pb, graphite, Ni and SUS 304 stainless steel exhibited a problem in terms of vigorous CO2 gas evolution. A specially baked RuO2/TiO2 mixed oxide electrode on a Ti substrate exhibited a problem in terms of service life. Finally, a low polarization, amorphous, insoluble electrode, which completely prevents CO2 gas evolution and possesses a reasonably long service life (∼4000h, at ia=20A/dm2) was found in Ir/Ta mixed oxide system. Pretreatment of the substrate, oxide composition, solvent selection and the baking temperature for the electrode were described. It is expected that the development of such a high performance electrode will render bath maintainance practicable.
It was hypothesized that in the absence of the action of the Lorentz force (rotary motion of an electrolyte) would be very small, and the influence of magnetic fields on redox reactions would show clearly. A low temperature plating bath including 26.7g·dm-3 of nickel hypophosphite, 12g·dm-3 of boric acid, 2.6g·dm-3 of ammonium sulfate and 4.9g·dm-3 of sodium acetate was adjusted to pH 6.0 with acetic acid or ammonia water. The amount of nickel deposition was inhibited and at a magnetic flux density of 0.2T its effect increased the deposition time to 12% after 1 hour and 26% after 12 hours. The inhibition effect after 12 hours was strongly apparent at a magnetic flux density of 0.1T, with the amount deposited was decreasing by about 20%. At magnetic flux densities over 0.1T, there was virtually no change in the effect. In terms of the crystal orientation of nickel deposits, the (220) face was more affected by the magnetic field than the other faces. Crystal orientation was relatively less as magnetic flux density became large, but deposition time and crystal orientation were not affected by magnetic field. Long-term change in spontaneous electrode potential was not influenced by a magnetic field in the plating bath, and no change was observed in deposition potential due to magnetic field in polarization curves in the plating baths. In nickel hypophosphite solutions, deposition potential was shifted by about 0.035V in the negative direction. Irrespective of whether a magnetic field was present or not, deposits exhibited adhesion and a lustrous appearance. In the absence of magnetic field, the deposits included 4.8% phosphor, and with a magnetic field present, phosphor content decreased to 3.6%, an inhibition ratio of 25%. It was concluded that magnetic fields exert an influence on the oxidizing reaction of hypophosphorous acid.
The adhesion strength between alumina ceramics and electroless Ni-P or Cu films was investigated in order to analyze the mechanism of adhesion between plated films and ceramics. The glassy parts, such as SiO2 located at the intergranular region in ceramics were selectively and effectively etched by HF solution. There is no clear relation between the mechanical properties of the metallized films and their adhesion strength, The etching amount greatly affected the adhesion strength, especially for the initial stage of etching, but the adhesion strength of the Ni-P film was always higher than that of the Cu film. The factors D/D0 and R/R0 were proposed as indicating the deposition condition at the interface between the plated films and ceramics, where D, D0 are the amounts of deposition at the substrate with and without etching, and R, R0 are film resistance on substrate with and without etching, It was confirmed that factors D/D0 and R/R0, effectively indicate the conditions of throwing power into minute etching pore at the initial deposition stage. From the values of D/D0 and R/R0, it was concluded that plated Ni-P film is deposited more effectively, and create a better anchor effect than plated Cu film.
Anodic coatings were formed on aluminum in 10wt% chromic acid solution by pulse current with a negative component to examine the effects of anodizing voltage, temperature and negative current density. It was found that thick coatings cannot be obtained when negative current is high, can when negative current controlled. The coating grows at the highest when the negative component is held to 11%. The cells of coatings formed by pulse current with a negative component were of more uniform size, pores were branching, and larger in size than with DC coatings. Many pores were observed in the barrier layer of anodic coatings formed by pulse current.
Specimens were electrolyzed by AC with various current waveform (sine wave, square wave and saw-tooth wave) and frequencies (10∼kHz) in NH4OH-NH4F system bath and NaOH-H2O2 system bath at a current density of 2A/dm2 for 30min, at 20°C. The use of a 10Hz square waveform resulted in a formation of a thicker film (5∼6μm) in both the NH4OH-NH4F and NaOH-H2O2 system baths. In the former case (NH4OH-NH4F system bath), film thickness decreased at frequencies above about 200Hz, reaching about 1∼2μm at frequencies above 1kHz. In the latter case (NaOH-H2O2 system bath), film thickness decreased according to increase of frequency, and it was about 0.5∼1μm in thickness at high frequency more than about 500Hz. The films anodized in the NaOH-H2O2 system bath with square current waveform was much rougher than those fromed using with sine or saw-tooth waveforms and larger pores were observed by microscope. Many large pores were observed in the coatings formed at high frequency and those formed in NaOH-H2O2 system bath had larger pores than those fromed in NH4OH-NH4F system bath.
Composite oxide films were formed anodically on hydroxide-covered aluminum in a boric acid/borate solution at 40, 60, 80, and 95°C, and then relaxed by allowing water to penetrate into the voids in the oxide films. After relaxation, specimens were re-anodized with a low current to measure the time-variation in the anode potential, Eref. The void distribution in the composite oxide films was determined by analyzing the Eref vs. tref curve. It was found that the penetration of water started after an induction period, and that the apparent activation energy for the relaxation of composite oxide films was 69.5KJ/mol. Voids were observed in high concentrations at the inner layer/outer layer interphase, and at the center of the outer layer in the composite oxide film. The total volume of voids increased with anode potential, Ea, during anodizing at all temperatures except 95°C; at 95°C, the void volume increased with Ea up to Ea=300V, and then decreased to a small value at Ea=400V. The void volume showed a maximum at 60°C for all values of Ea. Film formation mechanisms are discussed to explain how void distribution is established.