The relationship between grain boundary segregation and crack growth of stress corrosion and corrosion fatigue in 7050 aluminium alloy was investigated under various aging conditions in moist air environment. The effect of grain boundary segregation on fracture stress was also calculated using modified quasi-chemical approach. The results indicated that with increasing aging degree, the concentration of Mg segregated on grain boundary decreased and the ability of grain boundary to capture hydrogen was weakened, thus resulting in the decreasing percentage of grain boundary fracture stress reduction. It implied that the stress corrosion cracking susceptibility of the high strength aluminium alloy decreased and its corrosion fatigue resistance was improved.

The mechanism of inhibitor desorption from an anodically polarized electrode was studied on basis of electrochemical measurements. It was indicated that the inhibitor coverage on electrode surface remained unchanged in the range of applied potential lower than the desorption potential (Edes), and decreased rapidly as it reached the Edes. It was also showed that the inhibitor with stronger adsorbility possessed a relatively high desorption potential and that increasing inhibitor concentration and addition of chloride also resulted in a positive shift in Edes. The resistance of adsorbed layer to anodic dissolution, however,had begun to decrease gradually even before the potential reached the Edes. According to the analysis mentioned above, an assumption was proposed that the inhibitor desorption was caused by the lash of dissolving metal ions against the adsorbed inhibitor layer, and the large scale desorption occurred only after attainment of the desorption potential because the reabsorption rate of inhibitor for mending the inhibitor layer destroyed was lower than the desorption rate.

In acidic solutions containing propargyl derivative inhibitors,the changes in electrochemical parameters and inhibition performance with inhibitor concentrations were investigated using electrochemical measurements．It was found that in sulfuric acid solution there existed extreme values of double layer the contrary;this kind of extreme phenomenon was not observed in hydrochloric acid medium．By analyzing the changes in desorption potentials and corrosion potentials with inhibitor concentrations,the cause for this extreme phenomenon was demonstrated to be inhibitor desorption occurring around corrosion potential in sulfuric acid solution as the inhibitor concentration reached a certain value．

Both isothermal (at 1000℃,1050℃, 1100℃) and thermal cyclic(at 1000℃) oxidation performance of superalloys M17F and M17 in air were studied through TGA, XRD, SEM/EDAX and SEM/EPMA.The oxidation rate of M17F was much lower than that of M17, and the scale on M17F was more adhesive than that on M17. Such differences might result from the difference in the microstructure and refractory elements of the two superalloys. The irregular precipitation of γ' and/or (γ+γ')eutectic plates with higher Ti/Cr ratio resulted in rapid oxidation at the corresponding areas and thereby in the uneven scale on M17, while γ' precipitates were fine and dispersed in M17F. Furthermore, the rapid oxidation of the long strip-like MC carbides in M17 prevented the alloy from developing a protective scale. Elemental Ta in M17F brought about a Ta-rich oxide ribbon keying at the oxide scale/alloy substrate interface and thereby improved the cyclic oxidation performance of the alloy. Implanted Y+ favored the formation of a protective Cr2O3 layer in the scale and was thereby beneficial to the improvement of the oxidation-resistance of the alloy.

The potential distribution on external bottom of storage tank with cathodic protection is not uniform．The finite element method was applied to calculate the potential distribution and current distribution under various conditions．In the calculations various factors were considered, including soil resistivity,surface condition of tank bottom, number of anodes and their arrangement as well as cathodic polarization performance,etc．The analysis accommodated the combination of these factors as variable parameters．The results obtained could be used to interpret characteristics of the cathodic protection system．The calculation method can be recommended to engineering design for improvement of potential distribution.

Cathodic processes of iron in Fe2（SO4）3 and H2SO4＋Fe2（SO4）3 solutions were studied in the presence of 0．4T（tesla）magnetic field at 20℃．It was found that Fe3+ reduction and H+ depolarization accelerated each other in the absence of magnetic field．Magnetic field accelerated the cathodic process of iron corrosion in Fe2（SO4）3 solution or in 0．5 mol／L H2SO4 solution but did not cnange the reaction mechanism.In 0．5 mol／L H2SO4+Fe2（SO4）3 solution a combined effect of magnetic field on Fe3+ reduction and H+ depolarization reaction was observed．The results were explained on the point of view that magnetic field changed the mass transfer process and the structure of electric double layer at the electrode-solution interface．

The influences of implanted yttrium at doses of 1×10 17； 1×10 16；1×10 15Y+／cm2 on the high temperature oxidation behaviro of aluminized Ni-15Cr-6Al alloy were studied by electric thermal balance ,scanning electron microscopy（SEM）and X－ray diffraction(XRD).The results indicated that Y－implantation at the three doses had no effects on oxidation kinetics of the alloy．However，ion implantation dose of 1× 10 17 Y+／cm2 changed the oxide morphology and facilitated plastic deformation of the oxide scale， thus it altered the ways of stress relaxation in the scale and improved the scale adhension．The change of the oxide morphology might result from the change of growth mechanism of the oxide scale， Ion implantation doses of 1×10 16 1×10 15Y+／cm2 had only a little or no effect on the oxide scale morphology.

Specimens of 1Cr18Ni9Ti stainless steel were prepared by low temperature elongation deformation at－70℃ to obtain various martensite contents．The phase transition process was examined by TEM，XRD and metallography.Pitting susceptibility of the steel in 1 mol/L NaCl was evaluated by electrochmical hysteresis technique and polarization resistance measurements. Both α’－and ε-martensite were observed after the elongation deformation.The content of α’－martensite increased with increasing degree of deformation，while the amount of ε－martensite was consistently low and remained unchanged.These ferromagnetic phases had significant effect on the pitting susceptibility of the steel.When their content was less than 4．58％ or more than 25.5％，the pitting susceptibility increased with the increasing amount of ferromagnetic phases.In the range from 4.58％ to 25.5％，however，the specimens containing more martensite were found to be less susceptible to pitting．These findings were briefly explained.

The corrosion behavior of iron electrode in H2SO4 containing thioures（C 0．1 mmol／L）was investigated with polarization curves and EIS method．Various electrochemical parameters involved were obtained．The results showed that，the rate determining step（r．d．s）for anodic dissolution reaction of iron in low polarization region was a nucleophilic additive reaction,and the corresponding kinetics parameters were VTU=1,ba≈60mV.The r.d.s for its catbodic process was a Heyrovshky Heyrovsky reaction,and the kinetics parameters were：VTU＝－0．5，VH+=1．5，bc≈－82mV．

The low frequency short－crack propegation model for 16Mng steel in hydrogen was investigsted．The crack growth rates were calculated on the basis of elasto-plastic fracture mechanics using the formula da／dN—C（△J）n．The results showed that the relation of da／dN～ △J consisted of three sections. The threshold value △Jth for crack propagation was calculated and the crack propagation path was observed by metallograpy.

The causes of corrosion of casings at "Wen Well 10-1" were studied by visual examination of the corroded casing pipe and x-ray analysis of corrosion products. Results showed that inner corrosion was the primary factor for pipe perforation. The corrosion on the upper part of the pipe was more serious while that on the lower pat was slight. That corresponded to the different kinds of iron sulfides in the corrosion products. Labroatory tests were carried out for the effect of temperature on the growth of sulfate reducing becteria (SRB) and for the role SRB played in corrosion of casing pipe steel. Conclusion could be drawn that the corrosion product on the seriously corroded pipe was loose Fe9S8 while that on the slightly corroded pipe was mainly dense FeS.

In order to improve corrosion prevention performance of epoxy coating，a new polyurea/polyurethane(ATPU)－modified epoxy coating was synthesized．The changes of bonding strength to steel plate were examined after immersion in corrosives such as water，alkali，salt and organic solvents etc．Results showed that this modified epoxy coating possessed excellent bonding strength and chemical resistance．Accderated electrocheimcal measurements of the modified epoxy coated steel bar embedded in concrete also proved that the ATPUepoxy coating was significantly superior to the conventional polyamide epoxy coating in corrosion prevention.

The effect of rare earth addition to brush plating bath on structure and corrosion resistance of electrodenosited Ni－P alloy layer was studied．The results showed that the addition of 1g／L of blent rare earth could promote non-crystallization of the resulting Ni－P（RE）alloy layer，which was amorphous with even as low as only 5％ P．The Ni-P (RE) alloy had higher corrosion resistance than Ni-P alloy without rare earth in 3．6％ HCl solution and sea water．A mechanism of improvement was proposed．The rare earth ions might be adsorbed on the eledrode surface and interfered with normal discharge and diffusion of Ni2+ so as to promote the non-crystallization.

A new surface modiffication technique by direct exposure of the native passive film on 1Cr18Ni9Ti stainless steel to electron cyclotron resonance (ECR) nitrogen plasma at room temperature was described.The modification significantly reduced its susceptibility to pitting corrosion. The pitting corrosion resistance of the modified steel in 1%NaCl solution was comparable to that of AISI type 316L stainless steel.In general, a higher self-biasing potential and a longer modification time resulted in further improvement of the corrosion resistance.The X-ray photoelectron spectroscopy (XPS) analyses showed that the modified passivating surface predominantly consisted of the stable Cr2O3,FeOx oxides, and other chromium oxides such as CrO3 and CrO2, as well as some of carboxyl species with a little chromium nitride. These chromium oxides were enriched in the modified passive films and could act as a stable corrosion resistant barrier layer.