Although aluminide coatings have good oxidation resistant properties, their hot corrosion resistance is not satisfactory. It is thought that Cr-Al coatings may improve the high temperature corrosion resistance over that of aluminide coatings. Is it possible to produce a Cr-Al coating by a single step pack process? How good is the corrosion resistance of the Cr-Al coatings? These problems are discussed in this article. The experimental results show that it is difficult to obtain Cr-Al coatings on pure Ni by a single step pack cemenation process because aluminium deposited on nickle specimen and chromium powder reduces activity of chromium greatly, thereby hampering the chrominizing process. It is possible to form Cr-Al coatings by two-step pack processes. However the order of coating steps is very essential: a useful Cr-Al coating which can resist oxidation and hot corrosion can be produced by means of aluminizing after chrominizing, but an uncompact Cr-Al coating which contains many holes and doos not well resist oxidation and hot corrosion well be formed by chominizing.

The stress field around the notch tip of a mode Ⅱ notched specimen was analyzed by means of finite element method and the stress intensity factor K_(?)was calculated by J-integral. The results indicate that the maximum shear stress is located at 0=80°and its direction is α=5°, the maximum principal stress σ_1 and the maximum hydrostatic stress are both atθ=-110° and the direction of σ_1 is α=10°. Hydrogen induced cracking (HIC)and stress corrosion cracking (SCC) of a high-strength steel 34CrNi3MoA(T. S=1500MPa)under Mode Ⅱ loading were investigated using notched specimens. The results show HIC and SCC under Mode Ⅱ loading initiated at the maximum hydrostatic stress site. However, cracking is oriented along the shear stress direction at the site, not normal to the direction of maximum principal stress component. On the contrary if the specimens are loaded to fracture in air under Mode Ⅱ loading, cracking oringinates at the maximum principal stress site around the notch tip and the cracking direction coincides with the direction of the maximum shear stress. The above mentioned facts indicate that hydrogen induced delayed plastic deformation is a necessary condition for HIC; and the nature of SCC for high-strength steel in 3.5% NaCl solution is HIC. The results show that HIC and SCC under Mode Ⅱ loading can occur during dynamic charging with hydrogen and in 3.5%NaCl solution respectively. The normalized threshold stress intensity factors under Mode Ⅱ loading during dynamic charging in 1N H_2SO:+0.25g As_2O_3/l solution and in 3.5% NaCl solution are K F/K_(?) X=0.1 and K_Ⅱ SCC/K_(?) X=0.45, respectively. The corresponding values under Mode Ⅰ loading are K_Ⅰ H/K_Ⅰ X=0.02 and K_(Ⅰ)SCC/K_(Ⅸ)=0.37, where K_(ⅡⅩ)and K_(Ⅸ)are critical values loaded to failure in air under Mode Ⅱ and Mode Ⅰ loading respectively. Thus, (K_Ⅱ H/K_(ⅡⅩ))/(K_(Ⅰ) B-/K_(Ⅸ))=5 and (K_Ⅱ SCC/K_(Ⅸ))/(K_Ⅰ SCC/K_(;Ⅸ))=1.2 A typical intergranular fracture was observed during HIC and SCC under Mode Ⅱ and Ⅰ loading. But the fracture surfaces of specimens failed in air are composed of dimples for both kinds of loading.

The pit growth law has been derived in consideration of the ohmic potential drop inside a pit. The changes of the pitting corrosion current, Ⅰ, of the radius of the pit, r, and of the current density inside the pit, i_p, with time, t, can be expressed as Ⅰ∞t~b, r∞t~b_r, i_p∞t~b_i, respectively. The ranges of b, b_r, and b_i are 0.5～2, 0.5～1, -0.5～0. respectively. The pitting corrosion on the scratch scar of stainless steels in chloride solution has been investigated. In the early stage of the pit growth, the pitting current is proportional to tb and values of b fit well with those values calculated theoretically. It can be concluded that the ohmic potential drop is an important factor which has the influence over the pit growth kinetics.

Hydrogen induced cleavage fracture for Fe-3% si single crystal and polycrystals was investigated. The results showed that a cleavage fracture occurred during dynamic charging at the slow strain rate test or under constant load at room temperature, and hydrogen induced cracking under a Ⅰ+Ⅱ combined loading propagated along the(001)cleavage plane insead of the direction predicted on the basis of the fracture criterion under the combined loading. Macroscopic hydrogen intergranular fracture was a result of cleavage fracture along the (100), (010) and (001) planes in the immediate vicinity of the grain boundary. For the Fe-Si single crystal,da/dt vs K_1 curve also consisted of three parts and the plateau velocity under mode Ⅰ loading was larger than that under combined loading. Fractographic study and stress analysis indicated that a set of the<001> Sessile dislocation was just acleavage microcrack for the Fe-Si alloy. Hydrogen carried by the gliding dislocations would enter into the microcrack and the hydrogen pressure in the mierocrack could augment the external stress and promote the formation of a stable cleavage crack.

The effect of indium on the dissolution of aluminium sacrificial anode was studied. Results showed that the potential of Al-Zn-In anode shifted towards negative and its electrical efficiency descended with increasing amount of indium in alloy; indium segregated in such alloys; corrosion pits distributed uniformly on the whole surface of the anode, and the In-rich islands were discovered in these pits. U shaped curves of time versus the amount of indium dissolved were obtained. It is proposed that the In-rich segregated phase particles activate the dissolution process of aluminium sacrificial anode.

The chemical composition and crystallographic structure of chromate conversion coating on the surface of aluminum and its alloy were investigated by using infra-red(IR), X-ray diffraction, electron diffraction and DTA methods. It was found that the spectra of chromate conversion coating on the surface of aluminum and its alloy are similar to those of γ-CrOOH. Furthermore, a comparison of the IR spectra of the chromate conversion coating on the surface of aluminum with those for Cr_2O_3 indicates that the amount of Cr_2O_3 in the coating does not exceed 5％. The results of X-ray diffraction and electron diffraction measurements show that these chromate conversion coatings are non-crystalline. An appreciable exothermic peak at 310℃ was found on the DTA curve and it is due to the transformation of chemical composition and structure of chromate conversion coating on aluminum. The IR and X-ray diffraction spectra of samples subjected to DTA measurement(range of temp. 20-600℃, heating rate 10℃/min.)indicate the existence of crystalline Cr_2O_3.

The corrosion of cast iron by various sulphurous gases at high temperature follows the parabolic law, In this paper, the kinetics of corrosion of cast iron at high temperature in S, CS_2, H_2S and SO_2 of gaseous state are discussed with the principle of thermodynamics of irreversible process. Formulas of parabolic law are derived, and the mechanism of reaction is intererpreted.

The stress corrosion cracking(SCC)behavior of low carbon steel with hardness HRC less than 22, in 15% ethanolamine aqueous solution aerated with CO_2 gas at 100℃ was investigated using slow strain rate testing ((?)=6.4×10~(-6)s~(-1))under applied constant potentials. The experimental results show that carbon steel is susceptible to SCC in the "ethanolamine+CO_2" environment. The susceptibility to SCC occurs in the potential range of active-passive transition region, -0.40～-0.70V(SCE), of fast-slow sweep rate polarization curves, with highest susceptibility to SCC at potential of-0.65 V(SCE). The mechanism of SCC is mainly anodic dissolution. The SCC is characterized by decrease of reduction in area at fracture , appearance of secondary cracks on the surface of specimens, intergranular cracking mode and formation of passive film Fe_3O_4 during the polarization process. Based on the similarity between the main experimental results obtained under simulating conditions and the cracking characteristics of regenerating column, it could be concluded that the oeeurrance of cracks in the part of regenerating column for desulphurization operated at high temperature was mainly caused by the susceptibility to SCC of low carbon steel in the "ethanolamine+CO_2" solution.

The electrochemical behavior of alloy of Cu-Ni30 with film produced in 3％NaCl solution was studied by means of the electrochemical methods. This film prohibites anodic dissolution, it is just like a resistance. The cathodic reaction is stitl the reduction of oxygen in spite of being inhibited by the film, The difference between films produced by electrochemical polarrization and by immersed in 3％ NaCl solution are discussed.

The authors attempt to explore the corrosion tendency of metals in Fuzhou geothermal water with fhe aid of potential-pH diagram from the view of thermodynamics. This article reports the study of copper-geothermal water system. A programme has been worked out for using BASIC language to calculate the high temperature thermodynamic data on APPLE Ⅱ microcomputer, and the E-pH diagram of this system has been drawn with DXY-800 plotter. Simultaneously, the practical corrosion potential of copper in Fuzhou GW2 well geothermal water has been determined. The results show that in this water, a Cu_2O film probably grows on the surface of copper when the temperature is below 318K, and a CuO film when the temperature is above 318K. Both are situated in the passive. region.