Low temperature hot corrosion behavior of commercial pure iron coated with K_2 SO_4-Na_2 SO_4 was studied in O_2-0.1,0.5 and 1.0%(SO_2+ SO_3)gas environments in the temperature range of 560 to 750℃.The experimental results indicate that the low temperature hot corrosion of iron is caused by the formation of low melting ternary sulfate containing K,Na and Fe,and that the corrosion can be explained on the basis of dissolution-precipitation mechanism.

The bending method can be used to measure the stresses of the oxide scale directly in-situ during high temperature oxidation.In com- bination with the acoustic emission technique it was used to measure the critical stresses of the oxide scale of tantalum.The acoustic emis- sion can sensitively monitor ventical and parallel cracks of the oxide scale,while the weight gain curves only give information about vent- ical cracks.During the oxidation of tantalum at 500℃,550℃,600℃ in 1 arm O_2,the cracking stresses(σ_(max,c) represented by the maximum stresses)are 23.3,38.5,18,4×10~6 kgf/m~2 respectively.The cracking stresses are dependent on the oxidation temperature.SEM,X-ray diffra- ction analysis and optical microscopy show that this result is related to the density and type of cracking of the oxide scale.The less denser the oxide is,the smaller the critical stress is.The stresses causing blister-like cracks are larger than the stresses causing cracks along the grain boundaries.In a word,the oxide scale cracking not only depends on stresses,but also on other mechanical properties,

The characteristics of prior austenitic grain boundaries in tempered martensitic microstructure in relation to intergranular stress corrosion cracking of 30Cr3SiNiMoWV ultra-high strength steels were investigated mainly with Auger electron spectroscopy.The results showed that carbon and phosphorus segregated apparently at the grain boundaries.There is a very thin layer of carbide at the carbon enriched grain boundaries, where segregated phosphorus distributes randomly.The basic reason why this steel is susceptible to intergranular stress corrosion cracking is that the interface between the carbide layer and the matrix provides a strong trap for hydrogen and promotes the localization of anodic dissolution, while phosphorus hinders the formation of hydrogen molecules from hydrogen atoms.

Investigations on the features of electrochemical noises during pitting corrosion of iron and two sorts of stainless steels were carried out under potentiostatic conditions.The results show that the fea- tures of the electrochemical noises from the fluctuation of current are common to all the systems studied,namely,the fluctuation spikes rise linearly and decay exponentially.Curves of spectral power density (SPD)for all the systems studied show that the electrochemical noises are low frequency 1/f~n noise and turn to“whitenoise”at very low frequencies.The estimated values of n lie between 2 and 4 depen- ding upon the nature of metals and the applied potential.The equation of SPD proposed in a previous paper is confirmed by the data in this work and the variation of the value of n is discussed based on this equation.

The influences of applied potential,Cl~(-)-concentration and applied anodie current density on the characteristic parameters of electro- chemical noises during pitting corrosion were investigated.It was found that the effects of Cl~(-)-concentration and applied anodic current density on the apparent value of n of 1 /f~n noises were negligible, while the level of the“white noise”at very low frequencies Gw and the cut-off frequency f_c of spectral power density curves increased with increasing Cl~(-)-concentration and applied anodic current density and with raising of electrode potential if no real pits could be detected on the surface of passivated metals.It is inferred that Cl~(-)-concen- tration and applied anodic current density only influence the rate of occurrence of pit nuclei but do not influence the processes of growth and re-passivation of single pit nucleus,and that the resistance of passivated metals can be evaluated by Gw and f_(?) during pit incubation period.

A study on the dissolution of low carbon steel(AY 1,0.09C:0.37Mn; 0.22Si;0.018P;0.017S)in Zn-5%Al-RE(where RE stand for rare earth) alloy bath is carried out.The results demonstrate that severe corrosion occurswhen the dipping temperature is above 490℃(for 10min).The growth kinetics of the alloying layer can be divided int two stages,The continuod spalling-dissolving of the alloying layer at the second stage is thought to be the main cause of the serious corrosion of the steel. The incubation period of the alloying layer at the first stage is shortened by adding RE,but RE has no effects on the growth kinetics.This may suggest that RE has an ability to increase the wettability of Zn Al eutectic alloy with the low carbon steel.The apparent activation energy increases with an increasing amount of A1 in the bath,this reveals the inhibiting effect of A1.

The effective oxidation state of vanadate corrosion inhibitor is determined by rotating disk electrode(RDE)potentiometric titration using NaVO_3 and/or VOSO_4 respectively in the following deaerated aqueous solutions:(1)stainless steel in 0.5MH_2 SO_4,(2)mild steel in CO_2-saturated 20% monoethanolamine solution,and (3)titanium alloy in 3.0MH_2 SO_4.It is found that NaYO_3,as a compound of pentapositive vanadium,can passivate these active-passive metals,but VOSO_4,as a compound of quadripositive vanadium,can not,so the effective oxidation state of vanadate corrosion inhibitor in aqueous solutions is+5,not +4.It is also found that as an oxidizing inhibitor,various compounds of pentapositive vanadium are equivalent in passivation process of metals. The variation of critical passivation concentration of NaVO_3 to ω~(-1,2)(ω-angular velocity of RDE) indicates that the passivation process of titanium alloy is determined by the diffusion rate of NaVO_3 in H_2 SO_4 solutions and one electron reduction to quadripositive vanadium takes place at the surface of titanium alloy.

The effects of stress components on stress corrosion of notched brass specimens under Mode Ⅱ loading in 1N NH_4 OH+CuCl_2 5g/1 aqueous solution were investigated.Based upon the experimental results, including threshold values under static loading,the effects of alternating loading and room temperature creep,as well as metallographic observations of the fractography,it is concluded that notwithstanding stress corrosion or corrosion fatigue in aqua ammoniae,or fatigue in air,the cracks always initiate at the site subject to maximum normal stress(θ=-110°)along the notched surface,and then propagate along the maximum shear stress direction from that site(α=-35°).This indicates that normal stress component plays a dominant role in stress corrosion of this system,which is related to the anodic dissolution accelerated by normal stress component.

AC impedance techniques in a broad frequency range(0.01Hz-65kHz) are applied to some organic coatings on mild steel in 3% sodium chloride solution.The coatings studied include commercial emulsion paint,primers and electrophoretic ones.Models for the impedance behavior have been developed for different coating systems,and methods for the analysis of experimental impedance diagrams in terms of coating and interface properties and their changes during exposure to corrosive environments are discussed,and an assessment of the behavior of these coatings is made in the light of the analysis.

The electrodeposition of zirconium has been studied in molten Flinak electrolyte containing zirconium fluoride.A coherent,dense deposit of zirconium has been obtained.It is shown that there are two differ- ent mechanisms for electrodeposition of zirconium,i.e.,metalliding and electroplating,which depend on the electrode material used.X-ray diffraction analysis indicates that the microstructure in the zirconium deposit appears as a texture oriented preferably along Zr[110].A lustrous coating of zirconium with a surprisingly smooth surface may be deposited on copper substrate under appropriate conditions.The de- posit is identified by TEM as an amorphous alloy of Zr and Cu.

The effect of chemical pre-passivation and subsequent vacuum steam treatment on passive characteristics of stainless steels has been studied. Vacuum steam treatment promotes the passive film formation of the steels,and this process can be further improved by chemical prepassivity.The passive film stability of the steel treated by the new technique is much higher than that of the steel treated by classical un- vacuum steam treatment technique,its stable time at passive potential is almost 50 times as that of 0Cr18Ni19Ti and its passive current density is at least one order lower than that of 0Cr18Ni19Ti the pitting corrosion resistance in Cl~- medium is also improved a lot as compared with that of its original state.X-ray surface analysis has been used to discuss the mechanism of improving corrosion resistance by the new technique.

The effect of thermal-sprayed zinc(TSZ)and aluminium(TSA) on stress corrosion cracking susceptibility of 921 high-strength steel in seawater was studied by slow strain rate technique,with the porosity and local peeling of TSZ or TSA simulated,The test results showed that the potential of the steel coupled to zinc(about-1040mV, SCE)was in the potential range of remarkable hydrogen embrittlem- ent(HE)of the steel in artificial seawater.It would be very dang- erous to have TSZ applied on 921 steel as it might cause HE of the latter.On the other hand,the potential of the steel coupled to alum- inium(about-800mV,SCE)is in the safe and usable range with TSA providing good cathodic protection to the stressed steel component,

Mixing of Ta coating with Xe~+ or mixing of Cr coating with Ar~+ ions implantation in GCr15 bearing steel was studied.In the Ta-mix- ing case,about 6×10~(16) ions/cm~2 a dose was enough to make an amor- phous layer,and anodic polarization tests in chloric acid showed that the corrosion current was suppressed by nearly two orders.In the Cr-mixing case,a Cr_2 O_3 phase dominated layer was formed and the Cr/Fe ratio was measured after immersion test in FeCl_3.The Cr concentration decreased abruptly inside as compared with that of out- side of the pit.