The history of protective coatings for superalloys is traced, and the traditional high temperature protective coatings presently used in gas turbine airfoils are described，including diffusion coatings, MCrAlY overlay coatings and thermal barrier coatings. Several new concept coatings, such as microcrystalline coating, equilibrium coating (EQ coating), functionally graded coatings and smart coatings, and glass-based high temperature coatings are briefly introduced. Recent progresses in high temperature protective coatings are reviewed, including oxidation and /or corrosion resistant coatings, thermal barrier coatings and diffusion barrier coatings. The most fruitful progresses achieved were in the field of thermal barrier coatings, not only promising top ceramic materials but also advanced processing routes have been extensively investigated. Finally the development prospect of high temperature protective coatings is also discussed.

Abstract：Sulfur deposition had the effect on corrosion of N80 carbon steel, which was studied in high acid environment of Puguang gas field, then the corrosion production was analyzed by E-SEM. The mass loss method compared the effects of sulfur in various forms (blank, sulfur powder and molten sulfur coverage on the carbon steel) for carbon steel corrosion in environment, and the electrochemistry method discussed the corrosion process. The results showed that: the wet sulfur is mainly for local corrosion, sulfur had the direct contact with steel which would accelerate carbon steel corrosion. The electrochemistry method showed that elemental sulfur deposition accelerated carbon steel corrosion by promoting cathode polarization reaction process. The possible reason is that the sulfur catalyzed acid corrosion, thus resulting in the carbon steel corrosion.

The corrosion inhibition of gemini surfactant (12-3OH-12) and thiourea for Q235 steel in CO₂-saturated brine solution was investigated using mass-loss method, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results indicated that a synergistic effect is founded for the gemini surfactant and thiourea. The optium mixing ratio of the gemini surfactant to thiourea is 1:2.

A comparative study about growth characteristics of biofilm on the surface of Q235 carbon steel immersed in sewage from the gathering transportation pipeline of Shenli oilfield, was performed by using environmental scanning electron microscope (ESEM), energy disperse spectroscop (EDS), X-ray diffraction (XRD), while its influence on the corrosion behavior of the carbon steel was also examined by means of open circuit potential (OCP) and electrochemical impedance spectroscop (EIS). The results showed that a film of iron oxides formed in the initial stage of immersion. As the biofilm matured, the initial iron oxides were gradually converted to iron sulphides, to be a dense inner layer of the corrosion products scale, then numerous extracellular polymeric substances (EPS) containing carbohydrate appeared in the mature biofilm on the 8^th day. As a result of exfoliation of the films after 11 d immersion, pits ocurred on the surface. EIS data revealed that corrosion resistance of the steel increased while the dense biofilm formed on the surface. The charge transfer resistance R_ct decreased dramatically on the 11^th day was ascribed to the protective film cracked and thereby the corrosion was enhanced. During the later immersion period, a Warburg diffusion slope appeared at low frequency region instead of initial semicircle at high frequency region, which revealed that mineralization products might induce the increment of the diffusion barrier of the biofilms. In the meawhile, localized corrosion was activated due to the exfoliation of the biofilm.

A composite passivation film was prepared by using rare earth cerium salt and organic silane. Then the morphology and phase constituets of the film were characterized by scanning electron microscopy (SEM), X-ray scanning (XRD), and its corrosion performance was evaluated by measuring the hydrogen evolution in 3 mol/L HCL solution and immersion test in 0.2 mol/L NaOH. The results show that a pretreatment with saline solution was benefitial to the deposition of the rare earth Ce on the surface of galvanized steel, thereby a thicker conversion film containing rare earth Ce could be obtained. The corrosion resistance of the composite conversion film was superior to the single cerium salt conversion film without pretreatment with silane, as well as to the traditional chemical conversion film with chromate.

Abstract：The influence of DC stray current on corrosion behavior of grounding grid materials,Q235 flat steel,Q235 galvanized flat steel, copper in soil with 15% or 20% moisture content was investigated by means of electrochemical impedance spectroscopy(EIS), polarization curve technique and mass loss measurement. Results showed that in soil with 15% moisture content diffusion impedance of grounding grid materials showed a similar diagonal section with a 45° angle except Q235 galvanized flat steel, while all the EIS presented double capacitive loops with two time constants. Capacitive loop of three kinds of grounding grid materials were shrinked with 20% moisture content, meanwhile corrosion current density and mass loss rate were increased. In soil with the same moisture content, the capacitive loop of grounding grid materials were smaller with DC stray current rather than none, meanwhile the corrosion current density and weight-loss rate were increased. The corrosion resistance of the test materials may be ranked that copper is the best, Q235 galvanized flat steel is the second, Q235 flat steel is the worst.

Electrochemical corrosion behavior of a CT80 coiled tubing steel was studied by potentiodynamic polarization, electrochemical impendence spectroscopy and immersion test in an artifitial high salinity brine simulated Changqing’s oil well water at 60 ℃. The open circuit potentials of CT80 steel were changed with the corrosion time. The process of electrochemical corrosion was activation- and diffusion-controlled and the CT80 steel sample had a high corrosion rate. After pre-corrosion, a film formed on the surface of steel after a pre-corrosion treatment, therewith the polarization resistance was increased while the corrosion rate was decreased of the steel. The average corrosion rate of CT80 steel by the immersion test was decreased gradually with the increase of the immersion time, but serious pitting corrosion appeared on the surface of the sample.

Electrochemical impedance spectroscopy (EIS) was used to study the electrochemical corrosion behavior of carbon steel with a rust scale in 3.5%NaCl solution under UV irradiation. The results show that the UV irradiation may induce photocatalytic effect for the rust scale, which then accelerate the corrosion rate of the steel electrode. It is not clear yet whether all the three components γ-FeOOH, Fe₂O₃, Fe₃O₄ or one of them is responsible to the photocatalytic effect. In the long-term corrosion process, the corrosion of the rust electrode is heavier than the bare electrode; with the prolongation of time, the photocatalytic effect became stronger gradually with the increase of thickness of the rust scale, therewith the corrosion of the electrode was gradually increased. However, after 40 d exposue the rust sacle grew to a certain thickness, the corrosion of the electrode was slow down, whilst the photocatalytic effect of the rust scale maintained at a certain level.

The compatibility of a molten Al-4%Cu-12%Mg-7%Si alloy with several candidate vessel shell materials such as 304 stainless steel, 321 stainless steel, Ti6Al4V alloy and Ni plate for phase-transformation thermal storage facility was evaluated by means of immersion corrosion test at 650℃ for 360 h. The results show that corrosion mass loss of Ti6Al4V alloy was the least, followed by stainless steels, and Ni plate had the highets weight loss due to its dissolution reaction in the molten Al-alloy. An examination of the corroded alloys after immersion test was carried out by means of scanning electron microscopy (SEM). It was revealed that Ti enriched at the interface between Ti6Al4V alloy and molten Al-alloy, restricting the further growth of the interdiffusion layer; Ni element diluted and Cr enriched at the interface between stainless steel and molten Al-alloy. Ni-Al compound generated at the interface between Ni plate and molten Al-alloy, which then solute into the molten Al-alloy, therefore, Ni plate exihibits the worst compatibility to the molten Al-alloy.

Influence of cold-rolled deformation on the electrochemical performance of a cast Al-Ga-Sn-Bi anode alloy in 4 mol/L KOH solutions was investigated by measuring the corrosion rate, hydrogen evolution rate, discharge time, etc. The results show that cold-rolled deformation can improve the electrochemical performance of Al anode alloys. The alloy with 80% cold rolling reduction exhibits a lower rate of corrosion and hydrogen evolution, as well as a longer discharge time and thereby a good electrochemical performance.

Combination of high-energy ball milling mechanical alloying and spark plasma sintering was used to obtain ultrafine-grained stainless steel materials.The corrosion behavior in a mixture solution of ferric chloride and hydrochloric acid, alkali (NaOH), and formic acid were studied by potentiodynamic polarization technique. SEM and EDS are used to reveal the microstructure characteristics of corrosion products. The results show that in comparison with the ordinary rolled 316 stainless steel, the ultrafine-grained stainless steel showed a higher corrosion resistance, and among the three solutions the corrosion rate of the two steels in mixture of ferric chloride and hydrochloric acid is the highest.

The relationship of the probe potential and the real pipe potential have been set up experimentally and theoretically, which could be used to modify the potential recording of the polarized probe and obtain the real potential of the buried pipe.

n-Dodecytrimthoxysilane (DTMS) modified TiO₂ nanoparticles were prepared by the liquid phase deposition method. The surface morphology and particle size distribution of TiO₂ nanoparticles in the base oil were examined by transmission electronic microscopy (TEM) and Malvern laser particle analyzer respectively. The anticorrosion property of the lubricating Oil with addition of the DTMS modified TiO₂ nanoparticles was studied by electrochemical method and humidity cabinet test. The results showed that the agglomeration of particles was inhibited effectively by DTMS modification, and the particle size distribution in base oil exhibited a statistics distribution with a mean grain diameter of 60 nm. According to the results of electrochemical experiment and humidity cabinet test, the anticorrosion property of oil film was improved evidently by adding 5%TiO₂ to the base oil.

The effectveness of a chemical cleaning agent from Russia for removal of the deposits at the secondary side of steam generator of Tianwan nuclear power station was evaluated in this paper. The safety in the cleaning liquor for the structure materials at the secondary side was also concerned. The results showed that the dissolution rate of deposits in the cleaning liquor with the cleaning agent was about 14.80% at 90℃for 24h. In the liquor with the cleaning agent at 90℃, the corrosion rate of 0Cr18Ni10Ti stainless steel was very low, however, SA 508-Ⅲ was corroded severely; whilst, 0Cr18Ni10Ti was found to be insensitive to stress corrosion cracking.