The passive-active transition behavior of a 304 stainless steel was investigated by observing the self-activation behavior and nano-scale galvanostatic cathodic reduction experiment. The self-activation time, τ0 was dependent remarkably on concentration of sulfuric acid. It was appeared that applied nano-scale cathodic current density dissolved the passive film on a 304 stainless steel surface and shortened the activation time in galvanostatic cathodic reduction experiments. The applied cathodic current density was proportional to the reciprocal of activation time. From this linear relationship, the rate of the self-activation process, i0 was obtained. The i0 increased with increasing H2SO4 concentration. And i0 also increased with increasing passivation potential and passivation time. The stability of passive film increased in accordance with increasing τ0 and decreasing i0. Therefore, it was concluded that the stability of passive film on austenitic stainless steel is evaluated by the kinetic parameters of the self-activation rate i0 and the self-activation time, τ0.

The effects of W content and heat treatment on the hardness of Ni-W alloy deposits were investigated by XRD and Vickers microhardness test. The surface characteristics were also evaluated with respect to the surface roughness and glossiness. With increasing W content, the surface glossiness increased, but the surface roughness decreased. And the amorphous Ni-49wt.% W and 58wt.%W deposits had higher glossiness and lower surface roughness than crystalline Ni-W deposits. The hardness of Ni-W alloy deposits increased with increasing W content because of the solid solution hardening and grain size refinement. As the heat treatment temperature was increased, the hardness increased to reach the maximum of 1300VHN at 600 for Ni-58wt.%W deposit. The precipitation of intermetallic compounds such as Ni 4 W and NiW seemed to contribute to the increase of hardness. However, the hardness decreased at higher temperature than 600 owing to the precipitation of pure W, which was supersaturated in Ni matrix.

In order to investigate the corrosion behavior of TiNi shape memory alloy, especially electrochemical behavior of pitting and crevice corrosion in a human body, current density contour(CDC) map of TiNi alloy was constructed by potentiodynamic polarization technique in simulated physiological sodium chloride solutions of pH ranging from 1 to 13 at 37oC. Morphology of pits and corrosion products in sodium chloride solutions of various pH were analyzed by SEM and EDX, and susceptibility and mechanism of localized corrosion were also discussed.

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