Ni-P-SiC and Ni-P-diamond composite films were formed by electroless plating under various plating conditions, and the content of codeposited SiC or diamond particles was measured by membrane filtration. The effect of the suspension concentration of the dispersed particles and the flow volume of air bubbling on the content of codeposition was estimated. AC impedance was measured at the rest potential in the electroless plating solution, and based on the Cole-Cole plot and Faraday impedance plot, a codeposition mechanism is suggested. The effect of the addition of Tl+ was also evaluated by this impedance method
Composite coatings consisting of SiC particles codeposited into electroless nickel, electro nickel and copper matrix were produced, and their wear characteristics were examined by an abrasive wheel wear test. When the rate of deposited depth was constant, abrasion loss increased with increasing SiC particle size. Loss decreased with excessive SiC content in the deposition. It was found that the optimum rate of deposited depth lies between 60 and 80 percent. The wear characteristics of the composite coatings obtained by electroless nickel plating were better than those obtained by other platings.
The electrochemical impedance of coated metals was measured in 5% NaCl solution continuously over 100 hours of exposure. In order to investigate what role the substrate plays in coating corrosion, seven kinds of substrates, including Zn plated steel and alloy steels having Cu, Ti additives were used as test specimens, and were exposed artificially to anodic or cathodic polarization at controlled potential The investigated system is time dependent, so one should be able to monitor it in situ. The impedance characteristics of the system were derived from the continuous measurement of impedance during exposure and discussed as a function of exposure time Comparison of the results form impedance, and visual observations of coating blisters and cross-cut tests confirmed that AC impedance data can be used effectively to evaluate the effect of the substrate. It was found that anodic and cathodic polarization exhibit different impedance characteristics in all specimens. Alloy steels with Cu, Ti were found to provide greater protection than Zn-plated steels for both interface performance and substrate corrosion-resistance properties under anodic and free corrosion conditions However, alloy steels with Cu, Ti affords less protection than Zn plated steels under cathodic polarization.
Cr-C alloy plating from Cr (III) sulfate-carboxylate baths has been studied by Hull cell tests and ESCA analysis. Bright deposits were obtained from Cr (III) sulfate baths containing carboxylates such as oxalate, malonate, glycine and some oxycarboxylates. ESCA spectra of C 1s levels for the bright deposits revealed that some of the carbon exists as chromium carbide in the deposits and the rest as adsorbed to be the most feasible complexing agent for Cr (III) resulting in deposits in containing more chromium carbide.
The carbon contents in Cr-C deposits obtained from Cr (III) sulfate-ammonium oxalate baths changed from 0.8wt% up to 3.2wt% with increases in the oxalate concentration in the bath. The structure of the deposits changed from crystalline to amorphous at a carbon content of about 1.4wt%. With the heating of amorphous Cr-C alloy two exothermic reactions occurred-one at 250∼350°C due to crystallization of metallic Cr from the amorphous alloy, and the other at 610∼630°C due to the deposition of Cr7C3 in the Cr metal matrix. The Cr-C deposition and the evolution of hydrocarbon at cathode seem to be brought about by the reduction of oxalate to carbon on the electrode surface during Cr electrodeposition.
The deposition of zinc-nickel alloy on gold plated substrates from sulfate electroplating baths was investigated by potentiostatic electrolysis with respect to the effect of electrode potential on the composition of alloy deposits. The electrodeposits were analyzed by atomic absorption spectrophotometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and, for their metal element content, by anodic chronoamperometry. We found that since both zinc and nickel dissolved as divalent ions in sulfate solution and nickel is always included as metal element in alloy deposits by XPS studies, the analytical values obtained for the zinc and nickel elements by both anodic chronoamperometry and atomic absorption spectrophotometry permitted the evaluation of the content of metallic zinc and metallic nickel and the summation of zinc monoxide and zinc dihydroxide in alloy deposits as well. The partial quantity of electricity for deposition of metallic zinc sharply increased at potentials near -0.99V (Ag/AgCl sat. KCl). Both zinc monoxide and zinc dihydroxide were always included in alloy deposits obtained at potentials more noble than -0.99V and were never found at potentials of around -0.99 to -1.00V. At potentials less noble than -1.00V, however they were included in alloy deposits again when alloy deposition current and especially hydrogen evolution current increased.
Polarization behavior of an electroless copper plating solution containing EDTA as a complexing agent has been studied and the composition, surface appearance and cross section of the deposits have been investigated by electron diffraction analysis At 70°C, polarization behavior was explicable by the mixed potential theory at low concentrations of HCHO and copper complex ion CuY2- was found to be directly reduced to metallic copper The electron diffraction analysis of the deposit showed the deposition of Cu alone At 70°C and high concentrations of HCHO, however, the additivity of the polarization curves did not hold A two-step reduction of CuY2- took place, resulting in the codposition of Cu2O This is explained by the hypothesis that the alcoholate ion from the HCHO was adsorbed on the working electrode. The results obtained at 70°C and high concentrations of HCHO, were found to hold true also at 30°C The codposition of Cu2O influenced the surface appearance and cross section of the deposits
The authors previously reported single carbide layers of VC, NbC or Cr7C3+Cr23C6 were formed on the surface of steels immersed in molten borax baths containing Fe-V, Fe-Nb or metallic Cr powder When steels, carbide-coated by immersing in the first bath containing V, Nb or Cr element, were immersed in the second bath containing element different from that in the first bath, tow carbide layers were formed on the surface of steels The inner carbide layer was formed in the first bath and the outer carbide layer was formed in the second bath. Both carbide layers had similar composition and crystal structure to those of the carbide layers formed by the single immersion method, and no diffusion of elements into each layer were observed The thickness of the outer layer increased linearly with square root of the immersion time, and the growth rate of the layer was controlled by the diffusion speed of the carbon in the carbide layer, as the case by the single immersion method
Ultramicrotomy has been employed to prepare thin cross-sections of the Ni-P alloys electrodeposited onto copper substrates. It was found that ultramicrotomed sections as thin as 10nm or even less can be prepared successfully with negligible damage to the alloys. Subsequent examination of the sections in analytical and high-resolution transmission electron microscopy has shown that the alloys of lower phosphorous contents consist of thin layers of different phosphorous content and crystallinity. Microcrystallites, several nanometers in size, were revealed clearly at high resolution in the alloy containing 15at.% phosphorous where rapid decrease in crystal size has been reported by X-ray diffraction measurements. Additionally, ordered regions, a few nanometers in size, were revealed at high resolution in the Ni77-P23 alloy which has hitherto been regarded as amorphous. Further evidence for the presence of such ordered regions has been obtained by Fourier transformation of the high resolution images.