Hot corrosion behavior of commercial iron and Fe-Cr,Fe-Al alloys in the presence of a thin Iayer of Na_2SO_4 deposit was studied in O_2/SO_2/SO_3 gas atmospheres at 650～750℃. The reaction kinetics were monitored and found to be dependent upon temperature, gas composition and alloy element content. XRD, SEM, EPMA and chemical analysis were employed to characterize the corrosion products. The results showed that the corrosion product scale for each material tested was composed of a compact oxide plus sulfide layer and a porous Fe_2O_3 plus salt layet. The both layers increased in thickness with the proceeding of corrosion, and the compact layer grew faster than the porous one. On the basis of experimental results, an electrochemical mechanism is preliminarily proposed, and it is used to illustrate low temperature hot corrosion processes of iron base alloys.

Low temperature hot corrosion behavior of Fe-Al alloys was studied in the presence of a thin film of Na_2SO_4-K_2SO_4 deposit on their surfaces in O_2/SO_2/SO_3 gas atmospheres in the temperature range of 650～750℃。 The reaction kinetics were measured gravimetrieally,and the alloys corroded were physically examined and analyzed. The results indicated that the binary sulfate deposit induced more severe hot corrosion of the alloys than a unitary sulfate Na_2SO_4 or K_2SO_4 deposit did. On the basis of a discussion on the effect of the addition of either K_2SO_4 to Na_2SO_4 or Na_2SO_4 to K_2SO_4 on thermodynamics of the equilibrium of mixed salts,the accelerated hot corrosion of the alloys caused by the binary sulfate deposit is attributed to the earlier appearance of a ternary sulfate eutectic, Na_2SO_4-K_2SO_4-Fe_2(SO_4)_3,on the alloy surface.

The XPS,SEM, EDAX and electrochemical techniques were used to examine the characteristics of the chemical composition, structure and surface microscopic heterogeneity of the passive film on 18-8 stainless steel treated by a new electrochemical appreach. It was evident that the relative content of bound water and Cr species with high valence increased in the modified passive film. The modification of the physical defects on surface was observed after the electrochemical surface treatment. The nature and mechanism of the extremely high corrosion resistance of the modified passive film was discussed.

The charcteristie pitting potential measurements, scanning micro-reference electrode technique, XPS, electron probe, SEM were used to evaluate the suppression of the initiation and propagation of pitting corrosion of AISI 321 stainless steel in neutral NaCl aqueous solution by addition of Na_2MoO_4, HEDP+ZnSO_4 and their mixture. The results showed that Na_2MoO_4 is an efficient inhibitor for both the initiation and the propagation of pitting corrosion and has marked synergic inhibition with HEDP+ZnSO_4. The inhibition of the mixture inhibitor is related to the formation of insoluble MoCl_3. It is found that Cl~- content markedly increase inside and outside pits of the film and that the initiation potential E_z of instable micro pits raises, the difference between breakthrough potential E_b and E_z increases.

Stress Corrosion Cracking (SCC)of H62 brass in 1N NH_4OH+5g/L CuCl_2 solution under compressive stress was investigated using notched cross specimen and medifide WOL notched sample. The results showed that SCC could occur if an applide compressive load was larger than a critical value. The threshold stress intensity nucleating SCC from the notch under compressive stress was 20.7 MPam~(1/2), but the corresponding value under tensile stress was 3.5 MPam~(1/2). The fracture surfaces of SCC under compressive stress were quite different from those under tensile stress. The latter was composed of cleavage and quasi-cleavage, but the former was intergranular characterized by parallel striation pattern when K_1<15.3 MPam~(1/2) and mixed fracture when K_1>15.3 MPam~(1/2)(cross specimen). The dislocation structure under compressive stress was also different from that under tensile stress.

Being immersed in aqueous solution with Cl~- ions,specimens made from a iow alloy steel (A537cl1)or from a stainless steel (1Cr18Ni9Ti)were tested under cyclic liad. Thetests were interrupted on schedule to measure the diameters and depths of the pits on the surfaces of the specimens. Then, by using non-linear regression method,these experimental data were expressed with five kinds of probability distribution functions. Among them lognormal function was demonstrated to be the optimal distribution function with the highest correlation coefficient (>0.99). Moreover, the probabilistic distributions and their evolution behaviours seem to coincide with the stochastic model proposed by the authors and pickering's evolution theory of pitting.

The high temperature corrosion behaviour in SO_2-contaminated atmosphere of Rene 80 superalloy with two different microstructures, i.e. equiaxed-grain structure by conventional casting (C. C.) or columnar-grain by directional solidification (D. S.) was studied. Analysis were carried out on the longitudinal sections and fracture surfaces of the tested specimens by SEM, EDAX and EPA. Similar tests were also conducted in air in order to compare with the results in SO_2-containing atmosphere. The results showed that severe sulphidation-oxidation corrosion along the grain boundaries of the conventional-cast Rene 80 alloy occurred in SO_2-containing environment, which led to premature failure of the alloy. However, owing to the elimination of transverse grain boundaries, the sulphidation-oxidation corrosion of the directionally solidified superalloy was hardly observed, and the rupture life of the alloy in SO_2-containing environment kept the same level as that in air. It is suggested that the damage of the superalloy in corrosive environment at high temperature under applied load was due to the interaction of high temperature corrosion-creep and mierostructure of the superalloy.

The corrosion behavior of Ni_3Al(0.1B) treated with different ion beam techniques has been characterized by multi-sweep-cyclic-voltammetry and optical microscopy. The results revealed that the ion implantation, ion beam mixing and ion beam assisted deposition are very effective to reduce the corrosion rate, to improve the passivability and to increase the durability of specimens in 1N H_2SO_4 solution saturated with oxygen.

The two frequency method for measurring corrosion reaction resistance based on a. c. impedance and numerical integration has been proposed. The real part and imaginary part of the impedance of corrosion system can be calculated through numerical integration, and the corrosion reaction resistance can be obtained by solving the equations. Then it could be convrted into the corrosion rate. The method has the advantages of short measurement and high precision. According to the principle, a corrosion rate measurement system composed of TP801B single board computer, TPS01 1232A/D converter and the corresponding interface circuit has been set up. Both the module circuit and practical corrosion system were measured by means of the new apparatus. The comparison of the obtained results with the data measured by solartron 1250 FRA and the theoretical values was made. It showed that the proposed method and the newly set up apparatus is reliable. Since the data collection and process is controlled only by a single board computer, the apparatus is compact and low cost. It can be applicable to corrosion monitoring.

Creep behaviour of FeCrAl and FeCrAl-ZrO_2 alloys have been investigated at 600℃ under the stress of 115.2 MPa in corrosive environment. The corrosive environments under study include air, gas mixture of N_2-10％O_2-1％SO_2 and surface salt coating (75％Na_2SO_4+25％ NaCl) of 2mg·cm~(-2) in the gas mixture. With the dispersion of ZrO_2 partitles, creep rates of the alloy remarkably decrease and creep lifes remarkably increase and sensibility of creep fracture in the corrosive environments decrease. The corrosion process facilitates crack initiation and crack extension during the creep at 600℃ for FeCrAl and FeCrAl-ZrO_2 alloy.

The diffusion of hydrogen in electro-deposited Ni-P amorphous alloys with different phosphorous contents (e. g. 8,10,12,14wt. ％) has been measured using electrochemical technique. The hydrogen diffusivities in the alloys decrease as the phosphorous contents increase. The second round permeation transients show that the hydrogen trapping effects strengthen with the increase of phosphorous contents in Ni-P amorphous alloy. The relation between diffusion co-efficient of hydrogen and temperature is in agreement with the Arrhenius curve. When the phosphorous concentration is 12wt. ％, D=9.16×10~(-2)exp (-49500/RT) cm~2/sec, diffusion activation energy is 49.5kJ/mol. Passive films formed on Ni-P amorphous alloy in 0.1N NaOH solution have some influence on the apparent diffusivity of hydrogen. It is observed that the apparent diffusivities are less affected by polarized potentials in passive region but greatly in overpassive region.

Corrosion behaviour of 316L/25-22-2 austenitic stainless steel weld system in deaerated 1 mol/L H_2SO_4 (30℃) solution was comprehensively studied by metallographical examination, electron probe microanalysis, and electrochemical method, including the measurement of corrosion at controlled-potential and potential distribution determination. Results of electrochemical research show that only slight general corrosion occurs for this weld system in the active potential region and in the active-passive transition potential region, as well as in the passive-transpassive transition potenteal region. The weld metal is subjected to the dentritical intergranular corrosion, and the base metal to the intergranular corrosion in the transpassive potential region. The nobler the etching potential in the transpassive potential region and the longer the etchion time, the greater the intergranular corrosion rate will be. The welding metal and the base metal display the same tendency of corrosion in the medium and no deterioration results from the galvanic corrosion between them. By metallographical examination and electron probe microanalysis, it is found that the precipitation of σ-phase exists at the grain boundary of the welding metal.

Constant load and potentiostatic techniques were used to study the susceptibility of SCC for H62 brass in 0.1N NH_4OH+0.1g Cu~(2+)/L solution at 30℃. It was found that a critical potential existed in this system, being about —620mV(SCE), below which the SCC would not occur. Above the critical potential, the cracks propagating along the β′ phase which dissolved prior to α phase were observed with SEM and metalloscope, and the most sensitive potential for cracking was about —200mV (SCE). Also, the simulated occluded corrosion cell designed previously by the authors was modified and used to investigate the chemical changes within S. C. cracks of this system. As anodic currents passed the cell, the pH value of occluded cell (0C) solution dropped down from about 11 to 6. 2 or less, the Zn contents of the 0C solutions increased rapidly with time, and the Cu/Zn ratio on the surface of occluded specimens increased. These facts indicate that acidification within cracks existed and dezincification occurred at the crack tips for this system.