It was demonstrated theoretically and identified experimentally that the protection potential against pitting or crevice corrosion (Ep) was intrinsically the reversal potential of the current between the occluded cell and the external surface (ET). Below ET, the cathodic current flowed into the occluded cell, the pH value of occluded solution increased and Cl- migrated from the occluded cell to outside, resulting in an active-passive transition inside the pit or crevice. A simulated occluded cell was used to determine the ET at different propagating stages of the occluded cell for 1Cr13 and OCrl8Ni9 stainless steels. It was found that ET dropped suddenly as the pH value of occluded solution decreased below a critical value. ET was equal to the difference between the open-circuit potential of the occluded cell and the diffusion potential of the occluded solution into the bulk. The influencing factors of the Ep determintion and its poor reproducibility were also discussed.

The internal oxidation behavior of AgCu alloys with various Cu contents at 750℃ and 850℃ was studied by means of TGA, OM, SEM and HREM. After 12h oxidation of the alloys, it was found that, all Cu was precipitated as CuO particles for Ag-0.8at%Cu but not for Ag-3.3at%Cu and Ag-6.3at%Cu alloys, and CuO particles were precipitated homogeneously in the surface of samples of the above three alloys. The exception was the alloys with Cu contents more than 9.5%, in the surface of which appeared some protrusions containing a great deal of CuO particle clusters. The metallograph of cross sections of internally oxidized samples showed that the nucleation and growth of CuO precipitation varied with the Cu contents. The number of CuO particles precipitated per unit volume decreased with the advance of internal oxidation for Ag-0.8at%Cu, Ag-3.3at%Cu at 750℃ and Ag-0.8at%Cu at 850℃ but not for the other alloys. A certain degree of Stacking Fault Tetrahedron (SFT), which was believed to be a vacancy-type fault formed by the "Kirkendall" vacancies created during internal oxidation process was observed in alloys by HREM at atomic level. It was believed that the SFT produced in internal oxidation front might promote the diffusion of Cu as the nucleation for CuO precipitation. Meanwhile, methods for homogeneous precipitation of CuO particles in internally oxidized AgCu alloys were proposed.

The effect of piperidine (PD) on inhibition from the damage of passive film of Cr25 stainless steel in NaCl solutions of various concentrations was investigated by potentiodynamic anodic polarization, P-G transient response measurements and electrochemical impedance spectroscopy (EIS). The results showed that the stability of passive film on Cr25 steel was remarkably improved by PD. In NaCl solution, the "Critical Ratio" of PD concentration to Cl- concentration was determined: PD: Cl- = l:100-170 (mol.). When the ratio of PD to Cl- concentration was greater than the "Critical Ratio", film breakdown potential was almost not influenced by PD and Cl- concentrations. On the contrary, when the ratio was less than the criterion, the notable dependence of film breakdown potential on PD and Cl- concentration was observed. The inhibition mechanism of PD was discussed in terms of the competitive adsorption theory. The similarities and dissimilarities between Cr 25 and 304 stainless steels in inhibition of PD were compared. In addition, a physical model was suggested fof the explanation of the above-mentioned results on the basis of photo-electrochemistry and Mott-Schottky plots measurements.

The corrosion fatigue behavior of carbon steel in drilling fluids was investigated with a self-made rotary type bending corrosion fatigue testing apparatus under simulated drilling conditions. The hydrogen permeation into carbon steel in drilling fluids was studied by electrochemical method.Experimental results showed that sulfide addition into drilling fluid accelerated the corrosion fatigue failure of the steel by promoting hydrogen permeation. The imidazoline inhibitor (DPI-2) suppressed the generation of hydrogen atoms and hydrogen embrittlement and thus prolonged the corrosion fatigue life of carbon steel. Cathodic protection in a specific range of potential (-300～-700mV) could increase the corrosion fatigue resistance of carbon steel in drilling fluid, but excessive cathodic polarization would promote crack propagation and therefore would be harmful.

The influence of implanted yttrium at dose of 1 × 1017Y+/cm2 on the isothermal oxidation behavior of directionally solidified alloy Ni30Cr in air at 1000℃ was studied using TGA, SEM/EDAX, SEM/EPMA and XRD. The oxidation behavior of both transversal and longitidinal samples was similar despite of their difference in microstructure. Y+-implantation reduced the weight gain by a factor of 2-3 after 20h oxidation. A finer grain size scale formed on the Y+-implanted alloy. Preferred oxidation and internal oxidation along grain boundaries were eliminated and the formation and growth of interfacial voids were inhibited. Y+-implantation improvement might be due to the change of the growth mechanism of scale from predominant outward diffusion of cations to prevailing inward diffusion of anions.

By applying electrochemical methods, the time dependence of the influence of magnetic field on the polarization behavior for Fe/aqueous solution system was investigated. The results showed that the time effect was dependent upon the controlling process in electrode reactions. For the mass transfer process, the effect was instantaneous, while for the charge transfer process, it was memorial.

As a natural extension of our previous work, the novel wire beam electrode was used to study potential fluctuation of rust preventing oil film during its degradation. As a special electrochemical sensor, it remarkably improved the reproducibility of electrochemical tests. The error of electrochemical test may reduce to less than 5%. As a non-destructive and simple method, potential measurement had some advantages over other electrochemical testing methods. For example, polarization resistance measurement could breakdown the integrity of oil coating by DC current and EIS was time consuming. The electrochemical parameter and its category related to underfilm corrosion process could be measured directly using wire beam electrode. Potential fluctuation occurred on rust preventing oil film during its degradation, and the oil film had self-repairing ability. However, for the unoiled metal electrode and the electrode with base oil film, no such behavior was observed. Inhibitors in the oil film had direct effect on the self-repairing ability.

A new aluminizing method, the paste plasma aluminizing by hollow cathode, was developed. The optimum paste composition was obtained by orthogonal test method to be 40wt% Al, 5wt% NasAlFe, 5wt% KBF4, 50wt% SiC. The aluminizing was carried out at 1050℃ for 2h. The aluminized layer was 230 μm thick. The treatment increased oxidation resistance of low carbon steel by 2-3 times. The diffusion mechanism of this aluminizing process was discussed. Its advantages included quick diffusion speed, good surface quality and the possibility of localized aluminizing.

The corrosion rates of mild steel in soil was studied by means of polarization curve measurements on steel specimens with various extent of corrosion in laboratory. The surface of the corroded specimens and corrosion products were observed and analyzed by microscopy and X-ray diffraction. Emphasis was placed on the relationship of corrosion rate variations with time. The results showed that soil corrosion of mild steel was not only influenced by surrounding media but also controlled by the amout, structure and efflorescence extent of corrosion products at different stages.

In double glow plasma surface alloys, the depletion of some alloying elements in the surface layer was observed. Ion bombardment produced a seriously distorted layer beneath the sueface. The atom diffusivity in the distorted layer was higher than that in the undistorted layer. During diffusion process, the atoms gathered at interface of the distorted and undistorted layers. At the same time, the distortion gradient in the distortion zone supported this gathering. The sputtering and sputtering attenuation also promoted the generation of this inner peak of concentration. Mitigation or elimination of the depletion could be achieved by raising voltage and current of source plate, increasing metal atoms deposited on workpiece in unit time and carrying out high temperature diffusion after the plasma alloying.

The correlation of electronic structure to corrosion inhibition properties of aniline derivatives was studied in terms of semi-empirical quantum chemistry calculation. The results showed the protenated amino species of the p-substituted anlines to be the active part which could combine with metal. A mechanism of inhibition was suggested in which the p-substituted anilines, as inhibitor of iron in acidic medium, formed a film on the iron surface.

Neural network (BP algorithm) was applied to atmospheric corrosion of carbon steel and low alloy steels. After learning, the neural network could reflect relationships between meteoric factors, metallurgical factors and atmospheric corrosion performance of the steels. As demonstration, the effects of some factors were examined. The neural network was also used for prediction of atmospheric corrosion of several other steel. The accuracy of the prediction was dependent on accuracy and typicality of training samples.

By looking though the research activities conducted at home and abroad, various experimental techniques for investigation into corrosion failure mechanism of organic coatings were reviewed. It should be pointed out that materials and their environments should be considered as a whole from the system science point of view. The extraordinarily important role of electrochemical impedance spectroscopy (EIS) was emphasized. It was concluded that an appropriate coating life model and an expert system for life prediction should be set up on the basis of further research of failure mechanism of coatings.