The corrosion behavior of Zn and Zn-Al plating samples was investigated based on the measurement of anodic and cathodic polarization curves, the change in potential with use of a constant current of 2mA, the observation of structures in a cross section after a corrosion test, and the identification of corrosion products in the samples. Two plating samples were examined. One was fabricated by the dipping of the steel in a Zn bath at 743K for 60s, and another was fabricated by dipping steel in a secondary Zn-Al bath at 693K for 60s after first dipping in a Zn bath. The potentiostatic corrosion was carried out in a 3% by NaCl aqueous solution at 303K with a potential scan rate of 30mv/min and Ag/AgCl was used for the reference electrode. The galvanostatic corrosion was carried out in a 0.5% by NaCl aqueous solution with a constant current of 2mA/dm2. The change in the potential of the sample was measured, After the corrosion test, the samples were examine using EPMA and X-RD, Polarization curves obtained indicated that the reaction of Zn and Zn-Al coatings was controlled by control of the cathodic reaction. The rate of the cathodic reaction was faster for the Zn-Al coating than for the Zn coating. The same tendency was observed with Zn-Al alloy layer (Fe4Al13-Zn) and Zn alloy layer (ζ). During galvanostatic corrosion, corrosion proceeding through the η phase was observed between the lamellar ζ phase in the Zn plating sample. The contrast, the Fe4Al13-Zn phase dispersed in a Zn-Al matrix in the Zn-Al plating sampls, and the corrosion path was more complicated than with in the Zn plating sample. The time to reach galvanosttic corrosion of the base metal is thus believed to be determined by the difference in the corrosion path.
Aluminized steel sheets are promising materials for use as maintenance-free roofing or siding because of their superior corrosion resistance in comparison to galvanized steel sheets in a corrosive atmospheric environment. In this paper, the corrosion behavior of aluminized steel sheets has been investigated using test panels exposed for over 30 years. Corrosion of aluminized steel sheets was slight and their surfaces were covered with corrosion products mainly containing Fe. This Fe corrosion product seems to improve corrosion resistance by restraining the cathodic reaction. Corrosion products containing Fe seem to form minute α-FeOOH due to the effects of Al cations solved from the plating layer, preventing sources of corrosion like oxygen from diffusing into the plating layer.
Electrodeposited tin-silver eutectic alloy is a promising candidate to replace tin-lead solder coatings and provide superior thermal fatigue resistance. Eutectic tin-silver alloy film was deposited at 0.2∼5A/dm2 and at 25°C in a methane-sulfonate bath using the additives L-cysteine, 2, 2′-dithiodianiline, and polyoxyethylene-α-naphthol. The coexistence of these additives markedly inhibited preferencial deposition of silver over a range of low current densities. Tin and silver ions in the effluent were separated as hydroxide, and the residual concentration of tin and silver ions decreased to less than 0.01mg/L. Eutectic tin-silver alloy film consists of β-Sn and ε (Ag3Sn) phases, and its solidus temperature was 221°C. Whisker were not observed on the alloy film of the copper substrate after one year of aging at 50°C.
To improve the corrosion resistance of Ni-PTFE composite film, electrodeposition of Au, Cr and Sn on it to form Metal/Ni-PTFE (polytetrafluoroethylene) composite film was attempted in this study. Ni-PTFE composite film which was water repellent was wet enough under cathodic polarization in the electroplating solution for electrodeposition of the metal to take place. The contact angles of the waster drop of Ni-PTFE and Metal/Ni-PTFE composite films (Meta=Au, Cr, Sn) were 155°, 153°, 145°and 151°, respectively. The electric resistance on the surface of Ni-PTFE and Metal/Ni-PTFE composite films were 1.44×10-3, 5.25×10-4(Au), 3.61×10-1 (Cr), and 9.33×10-4 (Sn) ohm m-1, while that on Ni was 5.41×10-4 ohm m-1. The significantly larger electric resistance of Cr/Ni-PTFE composite film is through to be caused by the formation of an oxide such as Cr2O3 on its surface after the electroplating. This is also reflected in the fact that Cr/Ni-PTFE composite film has the smallest corrosion current among the Metal/Ni-PTFE composite films in this study. From the results of the corrosion test in 1mol dm-3 HCl aq., the amount of Ni dissolved from sample increased in the order of Ni-PTFE, Sn/Ni-PTFE, Cr/Ni-PTFE, Au/Ni-PTFE. The change in the wettability of the sample might affect the corrosion behavior in this case.
After the possibility of penetration hardness measurements by using a nanoindenter was examined, the penetration hardness of silicon nitride thin films produced under various depositing conditions was measured. Adhesion of thin silicon nitride to a stainless steel of SUS310 substrate was done through use of an arc ion plating process. For this process, the voltage of the substrate bias was changed ranging from -200V to -600V, the gas pressure in the plating chamber was 1.3×10-2∼6.7×10-2Pa, and gas formation was examined comparatively for 100% N2 and mixed gas of 50% N2/50% He. The substrate temperature remained constant at 580°C and electrode voltage was 50V. The following conclusions were obtained. 1) A high pressure and a mixture of N2 and He in the chamber resulted in superior hardness for the deposited films. 2) The maximum penetration hardness of the silicon nitride films was 45.0GPa. When converted into microvickers hardness, the maximum value became 2410.