The effect of calcium sulfate deposit on hot corrosion of iron-and nickel base superalloys was studied by coating various alloy samples with salt films of calcium sulfate and heating them up to 1000 and 1150℃.Kinetics curves were run for the alloys under study.Corrosion products were analyzed by X- ray diffraction,electron diffraction and electron probe analyses as well as by metallographic techniques.Experimental results showed that hot corrosion caused by CaSO_4 is highly composition dependent.Corrosion becomes more severe with increasing temperature and larger amount of salt coating.Mo-con- taining alloys with enough Al to give protective films of Al_2O_3 show catas- traphic corrosion due probably to the formation of liquid calcium molybdate. Increasing the Cr of content of the alloy raises its hot corrosion resistance,as is also evidenced by enhanced corrosion resistance of the less resistant alloys with chromizing.The mechanism of corrosion caused by CaSO_4 deposit is proposed.

X-ray photoelectron spectroscopy(XPS)and Auger electron spectroscopy (AES)techniques were employed for analyzing the surface films formed on Mo in various solutions and under different potential-pH conditions.The measurement results show:1)The passive film of Mo formed at lower poten- tials is an oxide or hydrated oxide with a lower valence(most probably tetra- valence),which is stable in the solutions free from oxygen.This film is extre- mely thin but excellently protective;2)The stable substance in the surface films formed in the transpassive region at higher potentials is molybdic anhy- dride MoO_3;3)The surface films formed in FeCl_2 solutions in the second passive region at higher potentials contain an outer layer of Fe_2O_3 and an inner layer possibly composed of ferrous molybdate.The AES and XPS results substantiate the validity of the previously presented potential-pH equili- brium diagram for the Mo-H_2O system and mechanism of the effect of Mo on the propagation of localized corrosion of steels.

Electrochemical technique and Auger electron spectroscopy(AES)were employed for studies on the effect of aqueous corrosion of iron by means of ion beam mixing in order to envisage the possibility for developing a new approach in surface modification of materials. Fe specimens were deposited with Cr(～400)in vacuum and then bom- barded by argon ion beam at the dose range of 1·10~(14)～5~(15)Ar~+/cm~2. In comparing ion beam mixed specimens with unmixed ones,it is found that ion beam mixing reduces the anodic current I_i and I_m in anodic potentio- dynamic polarization curves by approximately one order of magnitude.This beneficial effect increases with bombardment dose of argon.AES result shows that this beneficial effect is mainly related with the formation of passive film with chromium oxide on the bombarded surface.And it is presumably associated with the formation of metastable phase on mixed boundary between the deposited layer and substrate. Transmission electron microscope examination has revealed that argon bub- bles were formed as main physical damage in mixed boundary layer and sub- strate in close vicinity to the original interface during argon bombardment.

It is shown that the penetration of chemicals into polymers can be eva- luated by the change of electrical resistance of exposed polymers.Results of bisphenol A unsaturated polyester(323 resin)in 10% sodium chloride and epoxy resin(E-44 resin)in 25% sulfuric acid as a function of temperature are in accord with Arrihenius equation.The time-dependence of diffusivity of sulfuric acid into E-44 resin can be described empirically by the formula: D=Ae~(at).The effect of concentration of sulfuric acid is rather complex:at lower concentrations,the diffusivity of acid into E-44 resin decreases with increasing concentration,which is governed mainly by physical diffusion, while at concentrations higher than 30%,an increase in diffusivity is obser- ved,which is attributed to chemical reactions.It seems that the technique described can be employed to monitor practical performance of plant equip- ments on account of its high accuracy and ease of operation.

The corrosion products on both corroded blades from service and corro- ded specimens from test rig as made of cast nickel-base superalloy K-3 and coated with aluminide are examined by optical microscope,X-ray diffraction, SEM,EDAX and chemical analyses to explore failure mechanism.It is shown that sulphurization and hot corrosion caused by molten salt are responsible to the failure of the blades,and it is suggested that the mechanism of hot eorro- sion of low chromium,refractory metal-rich K-3 superalloy is the synergism of sulphidation,basic fluxing and acidic fluxing.When the temperature is raised to about 900℃,the weight change during the hot corrosion propagation stage of this superalloy obeys a linear relationship with time after an incuba- tion period.In order to improve the hot corrosion resistance of conventional aluminide coatings,two kinds of aluminium-silicon coating technique are deve- loped.A diffusion-type slurry coating and a sintered slurry coating based on aluminium-silicon are evaluated in RFL burner rig tester by comparing with pack aluminide coatings.It is interesting to note that sintered Al-Si slurry coating as well as the diffusion-type Al-Si slurry coating exhibit a much better hot corrosion resistance than conventional pack aluminide coating. When specimens are exposed to combustion gases containing 50ppm sea salt,the Al-Si coatings protected K-3 superalloy for more than 200 hrs with- out any indication of hot corrosion,while the Al-coated K-3 snperalloy lasted only less than 50 hrs.

In this paper,the growth texture and the volume diffusion process of MoSi_2 produced in siliconizing of Mo metal have been studied by the method of x-ray diffraction and metallographic examination.The results show that MoSi_2 comprises cylindrical grains with<110>fibre texture,and that the tex- ture axis is parallel to the longitudinal axis of cylinder and to the direction of diffusion.The direction of the net volume diffusion current of Si atoms changes alternatively along[113]and [113]in a zigzag way with the appa- rent direction as<110>_o The formation of MoSi_2 primary cracks is in accord with the characteristics of diffusion.

A DTG-1 multi-purpose electrochemistry modulation spectroscopy device was assembled and constructed in our laboratory.The ECMS measurements were performed on some electrodes in different solutions.Some significant results have been obtained.In some cases,if polarized light is used,the absorption peak may become more distinct and the resolving power may increase.

A variety of metals,Fe,Ni,Mo,Zr,Nb,Cr,V,Ta,and their alloys have been tested with regard of their corrosion resistance against liquid Al-Mg alloy,which is used as a solvent for extracting fission products.Experiments were carried out at 650℃ for durations of 50-500 hours.The corrosion resis- tance was evaluated by the thickness of diffusion layer measured with metallo- graphic examination and by the weight loss measurements.This work reveals that most of the metals and alloys studied are severely attacked by liquid Al-Mg alloys.However,Nb and its alloys with small amounts of alloying elements (e.g.Nb-2Al,Nb-lCr)and Ta exhibit satisfactory corrosion resistance.