High Temperature Corrosion of Water Wall Materials T23 and T24 in Simulated Furnace Atmospheres

Candidate materials for water wall of supercritical and ultra-supercritical utility boilers,T23 and T24,were chosen as the experimental samples and exposed to oxidizing atmosphere,reducing atmosphere and oxidizing/reducing alternating atmosphere separately.The corrosion temperature was 450-550?C.The effects of oxygen con-tent and temperature on the corrosion in reducing atmosphere and alternating atmosphere were investigated.The scanning electron microscope(SEM) and energy dispersive spectrometer(EDS) were used to examine the corroded samples.The results show that the corrosion kinetics of T23 and T24 can be described by the double logarithmic equation and parabolic equation respectively.To describe the corrosion of materials accurately it is not sufficient to analyze the macro-mass gain and the macro-thickness of the corroded layer only,but the EDS should be applied to examine the migration depth of corrosive elements O and S.It is revealed that the corrosion becomes more severe when H2S is present in the corrosive gas.S is more active than O,and Cr can reduce the migration of oxygen but not S.The combination corrosion of S and O and pure [S] has a stronger corrodibility than pure H2S.T24 suffers the most severe corrosion at oxygen content of 0.8%.Corrosion is aggravated when the corrosion temperature is above 450 ℃ in the alternating atmosphere.T23 has better corrosion resistance than T24 and W contributes a lot to the corrosion resistance of T23.

Accelerated Corrosion of Pure Fe Induced by Gaseous ZnCl_2 at High Tempreratures

ZnCl2 is one of the dominant aggressive species in waste incinerators or other advanced combustion power generation systems. In this study, the influence of minor amount of gaseous ZnCl2 on the corrosion behavior of pure iron was examined at 600-800℃ in a pure oxygen environment. The corrosion rate usually increased markedly with increasing temperatures at a fixed ZnCl2 content or with increased ZnCl2 contents at a constant temperature. The corrosion products were composed of a thin outer layer of ZnFe2O4 spinel and an inner zone with a much thicker layer of Fe2O3, which exhibited a serious separation from the matrix. Moreover, a molten FeCl2 layer was observed at the scale substrate interface. The accelerated corrosion of pure iron was attributed to the existence of FeCl2 with low melting point on the metal surface, which destroyed the cohesion and adhesion of the oxide scale. The results are discussed in relation to the thermodynamic factors and the presence of volatile compounds in the reaction system.

Self-glazing SiC-andalusite Refractories for High Temperature Gasification Applications

The combination of SiC and andalusite with calcium aluminate binder for castables in high corrosive gasifying environments is a promising alternative refractory system for many different slag systems. After sintering,a glassy protective layer has been identified. Beside the interactions of the refractories with intermediate slag also the thermomechanical properties,the thermal shock performance and the microstructure have been evaluated as a function of different binder systems.

Colloidal Silica Sol Bonded Castables for High Temperature Applications

A colloidal silica sol bonded product range is introduced by an example targeting high temperature applications in steel making. Placement and setting characteristics are shown. The thermal mechanical properties and resulting advantages are presented as well as the performance enhancement in corrosion resistance. Properties are compared to a common ULCC product. Results of the industrial trial phase are discussed.

CO_(2) High Temperature Corrosion and Its Prevention of Chromia Forming Fe-base Alloys

High temperature corrosion of chromia forming Fe-base alloys by CO_(2) produces not only oxidation but also carburisation.The corrosion kinetics in CO_(2)-rich gas is found to be increased compared with that in air or oxygen.As a result,higher alloy chromium levels are required to achieve protective chromia formation in CO_(2).Corrosion reaction mechanisms in CO_(2) are examined and the internal carburisation of alloys in low carbon activity CO_(2) gases are analysed based on the variation of pO_(2) at the interface of oxide and metal.Carbon penetration through chromia oxide scale has been revealed by atom probe tomography.The strategies to resist CO_(2) corrosion are reviewed by alloying of Si and/or Mn,forming additional diffusion barrier layers,and by adding sulphur to modify oxide grain boundaries to reduce carbon diffusion along the grain boundaries.

INFLUENCES OF SMALL AMOUNTS OF Y AND Ce ON HIGH TEMPERATURE CORROSION PROPERTIES OF M38 ALLOY

High temperature corrosion properties of M38 alloy with and without 0.04 wt-%Y and 0.05 wt-%Ce additions were studied in equilibrated S0_(2)+0_(2)gas mixtures at 850℃and 900℃.It was found that adding Y or Ce decreased the corrosion rate of M38 and changed considerably the surface morphologies and composition of corrosion products on M38.The effectiveness of Y and Ce were also discussed.

Study of the Corrosion of High Alumina Refractories by Al_2O_3-CaO Slag as a Reactive Impregnation Mechanism

The corrosion of refractories results from reactive transport,namely,transport of agents and chemical reactions of these agents with impregnated medium. On one hand,the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand,chemical reactions may be very numerous and complex.This study focused on the reactive impregnation of Al2O3- CaO slag into porous high alumina refractory. The transport properties of the refractory material were identified by means of a dedicated capillary rising test. Chemical reactions between the solid high alumina skeleton and Al2O3- CaO slag involve successive dissolution / precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system,the kinetics of these solid / liquid reactions is not well known.Corrosion tests associated with the quenching method,XRD analyses were performed for a better understanding of the kinetics. The results of this study open up a coupling approach for predicting the corrosion wear of refractory.

Achieving ultra-high corrosion-resistant Mg-Zn-Sc alloys by forming Sc-assisted protective corrosion product film

The weak corrosion resistance of magnesium and its alloys greatly limited the industrial application.Though functional self-healing coatings have been proposed as countermeasures,repeated damages on coatings under practical installation and complex external environments could require self-adaptive cor-rosion protection against multiple abrasions.In this study,an ultra-high corrosion-resistant Mg-1Zn-1Sc(wt.%)alloy with a corrosion rate of 0.087 mm/y has been designed and prepared,which has fine grains and uniform structure of a nano-scale ScZn phase with low potential.A unique and dense corrosion prod-uct film with a three-layered structure was found and studied on Mg-1Zn-1Sc alloy,providing excellent corrosion protection.In addition,the formation and protection mechanisms of the three-layered corrosion product film on Mg-1Zn-1Sc alloy have been discussed and proposed.The growth behavior of protective corrosion product film could be driven by the synergy of Sc and Zn elements.Furthermore,with the in-crease of Sc content,the strength,plasticity,and corrosion resistance of Mg-1Zn-x Sc(x=0,0.2,0.6,1.0,in wt.%)alloys increased simultaneously.The high corrosion resistance and moderate mechanical perfor-mance qualify Mg-1Zn-1Sc alloy as a promising candidate for diverse industrial applications.

Development of a two-dimensional bipolar electrochemistry technique for high throughput corrosion screening

Bipolar electrochemistry allows testing and analysing the crevice corrosion,pitting corrosion,passivation,general corrosion,and cathodic deposition reactions on one sample after a single experiment.A novel two-dimensional bipolar electrochemistry setup is designed using two orthogonal feeder electrode arrangements,allowing corrosion screening tests across a far wider potential range with a smooth potential gradient to be assessed.This two-dimensional bipolar electrochemistry setup was applied here to simultaneously measure for the simultaneous measurement of the nucleation and propagation of pitting and crevice corrosion under a broad range of applied potential on type 420 stainless steel,which has a very short localised corrosion induction time.It reduces the error from corrosion induction to corrosion competition,and all pits and crevice corrosion have no lacy cover.Results show crevice corrosion can gain current density and easier to support its nucleation and propagation at different potential regions more easily than pitting corrosion.

Uniform corrosion behavior of FeCrAl alloys in borated and lithiated high temperature water

The uniform corrosion behavior of model FeCrAl alloys as well as commercial Zircaloy-4 as reference material were investigated in 360℃borated and lithiated water.The results reveal that FeCrAl alloys exhibited better corrosion resistance than Zircaloy-4.It is found that the oxide films formed on the FeCrAl alloys are composed of outer Fe_(3)O_(4)layer,inner layer consisting of compact spinel layer and porous spinel layer,and transition layer containing Al-Cr-rich oxides and matrix enriched with Fe°.The spinel oxides in the inner layer are FeFe_(2-x-y-z)Cr_(x)Al_(y)MozO_(4).The corrosion mechanism of FeCrAl alloys in high temperature water is discussed.

Proton irradiation assisted localized corrosion and stress corrosion cracking in 304 nuclear grade stainless steel in simulated primary PWR water

Localized deformation and corrosion in irradiated 304 nuclear grade stainless steel in simulated primary water were investigated.The investigation was conducted by comparing the deformation structure,the oxide scale formed at the deformation structure,and their correlation with cracking.The results revealed that increasing the irradiation dose promoted localized corrosion at the slip step and grain boundary,which was primarily attributed to the strain concentration induced by enhanced localized deformation and depletion of Cr at grain boundary.Further,a synergic effect of the enhanced localized deformation and localized corrosion at the slip step and grain boundary caused a higher cracking susceptibility of the irradiated steel.

What is going on in magnesium alloys？

China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin （2015） and Chongqing （2016） China, respectively. A number of crucial research inter- ests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows： i） Plastic deformation mechanism and strengthening strategy, ii） Design and development of new Mg-based materials, iii） Key service properties, and iv） New processing technologies.

Effect of TiN diffusion barrier on elements interdiffusion behavior of Ni/GH3535 system in LiF-NaF-KF molten salt at 700℃

A TiN interlayer with high electrical conductivity was prepared between the GH3535 alloy and the Ni coating as a diffusion barrier to elements interdiffusion with the goal of increasing the corrosion resistance of GH3535 alloy in molten FLiNaK salt at 700℃.Results indicated that Ni coating could be directly electroplated on the TiN coated GH3535 alloy without extra conductive transition layer.TiN layer showed excellent thermal and chemical stabilities at elevated temperature in this molten salt system,without phase decomposition.The Ni/TiN composite coating was stable enough to resist corrosion in LiF-NaF-KF molten salt at 700℃.Elements interdiffusion between the substrate and Ni coating could be effectively inhibited and the corrosion resistance of the alloy was greatly enhanced.Besides,the TiN interlayer remained continuous and well adhered to the Ni coating as well as the substrate after corrosion test.

Mechanical Property, Oxidation and Ablation Resistance of C/C–ZrB_2–ZrC–SiC Composite Fabricated by Polymer Infiltration and Pyrolysis with Preform of C_f/ZrB_2

CJC-ZrB2-ZrC-SiC composites were fabricated by polymer infiltration and pyrolysis （PIP） with a preform of G/ZrB2. The carbon fibers and the resin carbon were coated with ceramic layer after PIP in the com- posites. The composite presents a pseudo-plastic fracture due to deflection of cracks and pullout of fibers. The composite has a higher bending strength by this method in comparison with the conventional PIP process due to fewer heat treatment cycles. The static oxidation test shows that the mass loss of the composites is no more than 1% after 20 rain oxidation at 1100 ~C. The ＂core-shell＂ structure between ZrC-SiC ceramic and other phases plays a positive role in preventing the inward diffusion of oxygen. The ablation resistance of the C/C-ZrB2-ZrC-SiC composite samples was tested using a plasma generator. After ablation for 120 s, the mass and linear ablation rates of the composites are 4.65 mg cm-2 s-1 and 2.46 μm s-1, respectively. The short carbon layer shows a better ablation resistance than the nonwoven carbon fabric layer after the ceramic coating is peeled off because of its higher ceramic content.

Corrosion behavior of Ti60 alloy under continuous NaCl solution spraying at 600℃

The corrosion behavior of Ti60 alloy was investigated under continuous NaCl solution spraying at 600℃.Results indicate that the corrosion rate of the Ti60 alloy is lower than that obtained with the solid NaCl deposit film in HO+O.The outer corrosion products are compact layers mainly containing NaTiOand nanocrystalline TiO.The inner layer is mainly composed of TiO,Ti O and SnO.TiO has a lamellar structure,and TiO has a strip-shaped structure.A mixed corrosion mechanism including classic oxidation and active oxidation occurred under NaCl solution spraying environment:the first stage was controlled by the classic oxidation mechanism with the promotion by the active oxidation following parabolic curves,and the second stage was controlled by the active oxidation mechanism following a linear rise in the mass gain curve.The mixed corrosion mechanism between classic oxidation and active oxidation produced a relatively dense Ti oxides scale,which decreased the corrosion rate.

Effects of cutting parameter on microstructure and corrosion behavior of 304 stainless steel in simulated primary water

The influence of surface conditions on the corrosion behavior of engineering structures has been paid more attention.However,there is still a lack of systematic research on the effect of cutting parameters on material’s microstructure and performance in service.In this paper,the effect of cutting parameters on microstructure and corrosion behaviors of 304 stainless steel in simulated primary water is well investigated.The results show that different cutting parameters can cause the superficial layer a gradient microstructure with nanocrystalized layer on top and deformation band structures underneath.With the similar surface roughness,the deformation microstructure can be very different due to the different cutting parameters.The effect degree on the depth of deformation zone is feed rate>cutting depth>cutting speed.The larger feed rate,lower cutting depth,lower cutting rate may induce a deeper deformation zone.With the increasing depth away from the machined surface,the localized corrosion rate is decreased,and at the same depth the localized corrosion rate along the deformation bands is higher than that along the grain boundaries(GBs).The nanocrystalized surface has a smallest general corrosion rate due to the quick formation of Cr rich oxide film.However,once the corrosion penetrates through this nanocrystalized layer,subsequent preferential corrosion at deformation bands and GBs will dominate and may lead to the significant increase of corrosion rate of the component in high temperature pressurized water.

Effect of Zn on mechanical and corrosion properties of Mg-Sc-Zn alloys

The effect of different Zn concentrations(0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)on the microstructure,cor-rosion property,and mechanical property of Mg-0.3Sc-x Zn(x=0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)alloys was investigated.Here,MSZ1 alloy exhibits the highest corrosion resistance(0.194 mm/y)and appropriate mechanical properties with an ultimate tensile strength of 228 MPa and elongation of 19%.The superior corrosion resistance of Mg-0.3Sc-1Zn alloys is attributed to the homogeneous volta-potential distribution and the dense corrosion product film.With the increase in zinc content,the strength and plasticity of Mg-0.3Sc-x Zn alloys(x=0 wt.%,1 wt.%,3 wt.%,6 wt.%)improved to some extent.The precipitated ScZn phase plays the role of the second phase strengthening,which enables MSZ6 to obtain the maximum tensile strength.However,the ScZn phase with low volta potential intensifies the galvanic corrosion,re-sulting in the decline of the corrosion performance.

Effect of temperature on corrosion behavior of alloy 690 in high temperature hydrogenated water

The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves, electrochemical impedance spectra （EIS）, scanning electron microscopy （SEM）, X- ray photoelectron spectroscopy （XPS） and transmission electron microscopy （TEM）. The corrosion rate of Alloy 690 reaches a local maximum at 250℃. The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200-300 ℃. A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.

Effects of surface grinding for scratched alloy 690TT tube in PWR nuclear power plant:Microstructure and stress corrosion cracking

Alloy 690TT tube samples with different scratch depths were repaired by grinding treatments using abra-sive papers of two different particle sizes.The microstructure and stress corrosion cracking(SCC)behavior were studied in detail.During grinding,the plastic accumulation zone vulnerable to SCC was removed.Meanwhile,some residual slip steps remained in the scratched area.Corrosion tests lasting 1000,2000,3000,and 4000 h show that the sensitivity and risk of SCC in the scratched area are decreased by grind-ing.Treatment using abrasive particles of a smaller size is more effective.Nevertheless,deep scratches remained hazardous even after the grinding.

Evaluation of Ni-Fe base alloys as inert anode for low-temperature aluminium electrolysis

Isothermal oxidation behaviors of Ni–Fe(wt.%)and of the same alloy with additions of 10 and 15%Cr alloys in the air at 800℃and 900℃and their anodic behaviors in aluminum electrolysis system at 800℃were evaluated.The composition morphologies of oxide scales were characterized by XRD,SEM,and EDS.Results show that the scales formed on Ni–Fe alloy at both temperatures consisted of an inner(Ni,Fe)Olayer and an outer FeOlayer.For Ni–Fe–10Cr alloy,an external(Ni,Fe)O/FeOlayers and an internal oxidation zone were formed at 800°C,while a continuous CrOlayer forms at the internal oxidation zone/substrate interface at 900°C.A multilayer structure oxide of CrO/(Ni,Fe,Cr)O/(Ni,Fe)O/FeOwas formed on Ni–Fe–15Cr alloy at 800°C,while at 900℃the FeObecomes discontinuous disperses in the(Ni,Fe)Olayer close to the surface.Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner CrOlayer and simultaneously reduce FeOcontent.After 4 h of electrolysis at an anode current density of 0.25 A cm,the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.