The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from composi...The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure-property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high- temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches, in each case, the effects on both the microstructure and the resulting properties are discussed.展开更多
An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate th...An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate the degradability and the mechanical integrity of the alloy.The results revealed that the degradation rate of the bone-plate increased in the first 7 days and then decreased with the prolonged immersion time before it finally reached a steady stage(about 0.84 mm/a)after immersion for 90 days.The bending strength after immersion for 60 days was 67.6 MPa,indicating that the bone-plate could support certain mechanical load after long term degradation.The formation of corrosion pits after degradation stemmed from the separation of the continuously distributed second phases from Mg matrix under the action of micro-galvanic couples.As a result,the mechanical performance of Mg-4Zn-0.2Mn-0.2Ca alloy was aggravated owing to the corrosion holes on its surface.展开更多
The effects of the addition of 5.0 wt.%Ni to an Al−6wt.%Cu alloy on the solidification cooling rate(T),growth rate(V_(L)),length scale of the representative phase of the microstructure,morphology/distribution of inter...The effects of the addition of 5.0 wt.%Ni to an Al−6wt.%Cu alloy on the solidification cooling rate(T),growth rate(V_(L)),length scale of the representative phase of the microstructure,morphology/distribution of intermetallic compounds(IMCs)and on the resulting properties were investigated.Corrosion and tensile properties were determined on samples solidified under a wide range of T along the length of a directionally solidified Al−6wt.%Cu−5.0wt.%Ni alloy casting.Experimental growth laws were derived relating the evolution of primary(λ_(1))and secondary(λ_(2))dendritic spacings with T and V_(L).The elongation to fracture(δ)and the ultimate tensile strength(σ_(U))were correlated with the inverse of the square root of λ_(1) along the length of the casting by Hall−Petch type experimental equations.The reinforcing effect provided by the addition of Ni in the alloy composition is shown to surpass that provided by the refinement of the dendritic microstructure.The highest corrosion resistance is associated with a microstructure formed by thin IMCs evenly distributed in the interdendritic regions,typical of samples that are solidified under higher T.展开更多
The ultra-high strength Cu-20Ni-20 Mn alloy was prepared by vacuum melting and its mechanical property and corrosion behavior were investigated. After thermomechanical treatment, the alloy exhibited an ultra-high tens...The ultra-high strength Cu-20Ni-20 Mn alloy was prepared by vacuum melting and its mechanical property and corrosion behavior were investigated. After thermomechanical treatment, the alloy exhibited an ultra-high tensile strength of 1204 MPa and the applicable elongation of up to 6.2%. With the increasing exposure time in 3.5% Na Cl solution, the corrosion current of the alloy decreased, while the polarization resistance and the charge-transfer resistance of the corrosion surface increased. The corrosion products formed on the surface of the alloy exposed for 1 d, and further corrosion made the corrosion product layer much dense, increasing the corrosion resistance and protecting the alloy from further corrosion.展开更多
The effects of chloride,sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking(SCC)test method using double cantilever beam(DC...The effects of chloride,sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking(SCC)test method using double cantilever beam(DCB)specimens.The SCC morphology was observed by using scanning electron microscopy(SEM)and the composition of corrosion products was analyzed by using energy dispersive spectrometer(EDS).The results show that the crack propagates to bifurcation in NaCl and Na2SO4 solution,while the crack in Na2CO3 solution propagates along the load direction.The SCC rate in NaCl solution is the highest,while lower in Na2SO4 solution and little in Na2CO3 solution.From the SEM morphologies,quasi-cleavage fracture was observed in NaCl and Na2SO4 solutions,but intergranular features in Na2CO3 solution.The mechanism of anion effect on SCC of steel 23Co14Ni12Cr3Mo was studied by using full immersion test and electrochemical measurements.展开更多
The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of ...The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of a series of corrosion level. Specimens either confined or unconfined were investigated for evaluation of the effect of confinement on bond strength and failure mode. Also, the tests were analyzed using nonlinear finite element analysis. It was shown that for both confined and unconfined steel bars, bond strength generally decreases as the corrosion level increases when corrosion level is relatively high. Confinement was demonstrated to provide excellent means to conteract bond loss for corroded reinforcing steel bars. It was shown that unconfined specimens generally split at a small slip with a large crack width and result in splitting failure while confined specimens contribute to a small crack width and generally cause a pullout failure. The analysis results agree reasonably well with the experiments.展开更多
The stress corrosion crack (SCC) susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique (SSRT), tensile with polarization and surface analysis technique. The curves o...The stress corrosion crack (SCC) susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique (SSRT), tensile with polarization and surface analysis technique. The curves of tf^Cl/tf^W -strain rate are divided into three regions: stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of εf^Cl/εf^W - strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy (SEM). SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The εf becomes the parameter to predict tf because the relationship between εf^Cl/εf^W and tf^Cl/tf^w is a straight line for AerMet 100.展开更多
Mg-Li alloy,as a superlight metallic engineering material,shows great potential in the fields of aerospace and militarydue to its high specific strength,better formability,and excellent electromagnetic shielding perfo...Mg-Li alloy,as a superlight metallic engineering material,shows great potential in the fields of aerospace and militarydue to its high specific strength,better formability,and excellent electromagnetic shielding performance.The research process ofMg-Li alloys is reviewed and three main problems are pointed out.Aimed at the poor corrosion resistance of Mg-Li alloys,thecorrosion behavior is mainly summarized.The surface treatment technologies,including electroplating,electroless plating,plasmaspraying,molten salt replacement,conversion coating,anodizing,micro-arc oxidation,organic coating,and organic-inorganic hybridcoating,are introduced in detail.Finally,the future development of corrosion and protection of Mg?Li alloys is discussed.展开更多
To describe the deformation and strength characteristics of the corroded rock-like specimens containing a single crack under uniaxial compression,a damage constitutive model combining hydro-chemical damage with coupli...To describe the deformation and strength characteristics of the corroded rock-like specimens containing a single crack under uniaxial compression,a damage constitutive model combining hydro-chemical damage with coupling damage of micro-flaws and macro-cracks is proposed.Firstly,based on phenomenological theory,the damage variable of the rock-like specimens subjected to water environment erosion and chemical corrosion is obtained.Secondly,a coupled damage variable for cracked rock-like specimens is derived based on the Lemaitre strain equivalence hypothesis,which combines the Weibull statistical damage model for micro-flaws and the fracture mechanics model for a macro single crack.Then,considering the residual strength characteristics of the rock-like materials,the damage variable is modified by introducing the correction coefficient,and the damage constitutive model of the corroded rock-like specimens with a single crack under uniaxial compression is established.The model is verified by comparing the experimental stress−strain curves,and the results are in good agreement with those provided in the literature.Finally,the correction coefficient of the damage variable proposed in this paper is discussed.The damage constitutive model developed in this paper provides an effective method to describe the stress−strain relationship and residual strength characteristics of the corroded rock-like specimens with a single crack under uniaxial compression.展开更多
Cold metal transfer(CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determ...Cold metal transfer(CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determined in terms of predicting the effect of welding process on the possible failures in their constructions caused by corrosive agents. The present study investigates the effect of heat input on mechanical properties and corrosion rate of AA5754-AA7075 joints welded by CMT using ER5356 filler wire. Pore formation was observed not only in the weld metal but also in the partially melted zone of AA7075 base metal due to the vaporization of zinc. Increased heat input caused over aging and zinc vaporization in AA7075 base metal, and grain coarsening in AA5754 base metal consequently decreased the tensile strength. The average tensile strength of AA7075-AA5754 joints varies between 235 and 240 MPa. The ductile fracture occurred at the AA5754 base metal side in all samples. Pitting was observed as the dominant corrosion mechanism. Corrosion resistance tended to increase with increasing heat input. Heat input values between 95 and 110 J/mm are recommended for the optimization of corrosion resistance and strength.展开更多
Considering the change of bond strength between corroded steel and concrete,flexural carrying ca- pacity of corroded reinforced concrete (RC) beam was calculated.On the basis of the condition of equilibrium of forces ...Considering the change of bond strength between corroded steel and concrete,flexural carrying ca- pacity of corroded reinforced concrete (RC) beam was calculated.On the basis of the condition of equilibrium of forces and compatibility of deformations for the whole beam,a model for the prediction of flexural carrying capacity of the corroded RC beam was proposed.Comparison of the model's predictions with the experimental results published in the literature shows the practicality of the proposed method.展开更多
In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests i...In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks' sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.展开更多
The effect of yield-to-tensile strength ratio(Y/T) on failure pressure of X70 pipeline without and with corrosion defects was investigated.The stress-strain response of materials was characterized by a power-law harde...The effect of yield-to-tensile strength ratio(Y/T) on failure pressure of X70 pipeline without and with corrosion defects was investigated.The stress-strain response of materials was characterized by a power-law hardening curve.Two formulas to estimate the strain hardening exponent n for a special Y/T were obtained by least squared regression method and the influence of Y/T on n was analyzed.As an application of n-Y/T expression,the analytical solutions of burst pressure for X70 pipeline without and with corrosion defects were also obtained.The results indicate that the burst pressure of defect-free X70 pipe without corrosion defects is a function of the Y/T,pipe geometry t0/D0 and engineering tensile strength,and increases as Y/T or t0/D0 increases; whilst the burst pressure of corroded X70 pipe decreases with the increase of defect depths,d/t.Comparisons indicate that the present analytical solutions closely match available experimental and numerical data.展开更多
The influence of exfoliation corrosion on the tensile properties of a high strength Al-Zn-Mg-Cu alloy was investigated by ambient temperature tensile testing, optical microscopy, transmission electron microscopy (TEM...The influence of exfoliation corrosion on the tensile properties of a high strength Al-Zn-Mg-Cu alloy was investigated by ambient temperature tensile testing, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). After exfoliation corrosion immersion, blisters and corrosion pits can be seen on the sheet surface, which lead to loss of materials and notches. A number of intergranular cracks are observed to initiate at the bottom of the corrosion-induced notches and propagate rapidly into the bulk materials during tensile. Consequently, exfoliation corrosion results in significant loss of strength and brittle fracture. EBSD results show that the crack propagation path is primarily along the grain boundaries with misorientation of-45°, and coincidence site lattice (CSL) boundaries are slightly more resistant to crack.展开更多
The marine structures such as harbour,pier and inshore concrete terrace are exposed in adverse circumstances in a long period of time .Owing to the attack of external corrosive medium,their safety,durability and relia...The marine structures such as harbour,pier and inshore concrete terrace are exposed in adverse circumstances in a long period of time .Owing to the attack of external corrosive medium,their safety,durability and reliability decline.Especially the reinforced concrete(RC) structures in the wave splash area are more likely to be subjected to destruction and the loss is vast. Now the safety ,durability and reliability of structure have become increasingly an important subject to be studied.By way of the soaking and drying cycle test on the different mix proportions oblique section of 10 pieces of RC beams suffered artificial sea water(ASW) corrosion under 0,35,70,105,140 times of dry-wet cycles,the compared results of exerting pressure test of these beams under simply supporting were investigated. The law about the changes of the mechanical performance for RC beams with different mix proportions under different time periods for suffering corrosion of dry-wet cycles is as follows: the resistivity to ASW corrosion of the concrete specimens with various water cement ratio(various initial strength)is different;the characters of oblique section failure for RC beams attacked by sea water are about the same as those for ordinary RC beam; along with the extension of the time for sea water attack, the bearing capacity for oblique section of RC beams varies wave upon wave.The specimens attacked by sea water for about 35 times of corrosion cycle achieve minimum bearing capacity.展开更多
Like reinforced concrete (RC) structure, Prestressed concrete (PC) structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride envi...Like reinforced concrete (RC) structure, Prestressed concrete (PC) structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems (staining, cracking and spalling of concrete). By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel (passive) and prestressing (active) reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.展开更多
Osmotic energy between river water and seawater has attracted interest as a new source of sustainable energy.Nanofluidic membranes in a reverse electrodialysis configuration can capture energy from salinity gradients....Osmotic energy between river water and seawater has attracted interest as a new source of sustainable energy.Nanofluidic membranes in a reverse electrodialysis configuration can capture energy from salinity gradients.However,current membrane materials suffer from high resistances,low stabilities,and low charge densities,which limit their further application.Here,we designed a high-performance nanofluidic membrane using carboxylic cellulose nanofibers functionalized with graphene oxide nanolamellas with cement-and-pebble microstructures and stable skeletons for enhanced ion transmembrane transport.By mixing artificial river water and seawater,the composite membrane achieved a high output power density up to 5.26 W m^(−2).Additionally,the membrane had an excellent acid resistance,which enabled long-term use with over 67 W m^(−2) of power density.The performance of this composite membrane benefited from the mechanically strong cellulose fibers and the bonding between nanofibers and nanolamellas.In this work,we highlight promising directions in industrial waste treatment using energy extracted from chemical potential gradients.展开更多
基金The Aluminium Corporation of China Ltd.(Chalco)for supporting aspects of this work financiallyproviding AA7150 materials as part of the Australia-China International Centre for Light Alloy Research(ICLAR)+1 种基金Monash University for developing the retrogression and reageing Matlab model (as part of the PhD project of Dr Adrian GROSVENOR)The ARC Centre of Excellence for Design in Light Metals and its Directors (first Prof Barry MUDDLE and then Prof Xin-hua WU) for supporting
文摘The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure-property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high- temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches, in each case, the effects on both the microstructure and the resulting properties are discussed.
基金Projects(2016YFB0301001,2016YFB0301101)supported by the National Key Research and Development Program of ChinaProject(51801004)supported by the National Natural Science Foundation of China+1 种基金Project(KM201710005005)supported by Beijing Municipal Education Commission,ChinaProjects(2172013,2192006)supported by Beijing Natural Science Foundation,China
文摘An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate the degradability and the mechanical integrity of the alloy.The results revealed that the degradation rate of the bone-plate increased in the first 7 days and then decreased with the prolonged immersion time before it finally reached a steady stage(about 0.84 mm/a)after immersion for 90 days.The bending strength after immersion for 60 days was 67.6 MPa,indicating that the bone-plate could support certain mechanical load after long term degradation.The formation of corrosion pits after degradation stemmed from the separation of the continuously distributed second phases from Mg matrix under the action of micro-galvanic couples.As a result,the mechanical performance of Mg-4Zn-0.2Mn-0.2Ca alloy was aggravated owing to the corrosion holes on its surface.
基金CNPq-National Council for Scientific and Technological Development(Grant:407871/2018-7)CAPES-Coordenação de Aperfeiçoamento de Pessoal de Nível Superior,Brazil,for the financial support。
文摘The effects of the addition of 5.0 wt.%Ni to an Al−6wt.%Cu alloy on the solidification cooling rate(T),growth rate(V_(L)),length scale of the representative phase of the microstructure,morphology/distribution of intermetallic compounds(IMCs)and on the resulting properties were investigated.Corrosion and tensile properties were determined on samples solidified under a wide range of T along the length of a directionally solidified Al−6wt.%Cu−5.0wt.%Ni alloy casting.Experimental growth laws were derived relating the evolution of primary(λ_(1))and secondary(λ_(2))dendritic spacings with T and V_(L).The elongation to fracture(δ)and the ultimate tensile strength(σ_(U))were correlated with the inverse of the square root of λ_(1) along the length of the casting by Hall−Petch type experimental equations.The reinforcing effect provided by the addition of Ni in the alloy composition is shown to surpass that provided by the refinement of the dendritic microstructure.The highest corrosion resistance is associated with a microstructure formed by thin IMCs evenly distributed in the interdendritic regions,typical of samples that are solidified under higher T.
基金Project(2017YFB0306105)supported by the National Key R&D Program of ChinaProjects(51601227,51701241)supported by the National Natural Science Foundation of China。
文摘The ultra-high strength Cu-20Ni-20 Mn alloy was prepared by vacuum melting and its mechanical property and corrosion behavior were investigated. After thermomechanical treatment, the alloy exhibited an ultra-high tensile strength of 1204 MPa and the applicable elongation of up to 6.2%. With the increasing exposure time in 3.5% Na Cl solution, the corrosion current of the alloy decreased, while the polarization resistance and the charge-transfer resistance of the corrosion surface increased. The corrosion products formed on the surface of the alloy exposed for 1 d, and further corrosion made the corrosion product layer much dense, increasing the corrosion resistance and protecting the alloy from further corrosion.
基金Project(51171011)supported by the National Science Foundation of China
文摘The effects of chloride,sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking(SCC)test method using double cantilever beam(DCB)specimens.The SCC morphology was observed by using scanning electron microscopy(SEM)and the composition of corrosion products was analyzed by using energy dispersive spectrometer(EDS).The results show that the crack propagates to bifurcation in NaCl and Na2SO4 solution,while the crack in Na2CO3 solution propagates along the load direction.The SCC rate in NaCl solution is the highest,while lower in Na2SO4 solution and little in Na2CO3 solution.From the SEM morphologies,quasi-cleavage fracture was observed in NaCl and Na2SO4 solutions,but intergranular features in Na2CO3 solution.The mechanism of anion effect on SCC of steel 23Co14Ni12Cr3Mo was studied by using full immersion test and electrochemical measurements.
文摘The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of a series of corrosion level. Specimens either confined or unconfined were investigated for evaluation of the effect of confinement on bond strength and failure mode. Also, the tests were analyzed using nonlinear finite element analysis. It was shown that for both confined and unconfined steel bars, bond strength generally decreases as the corrosion level increases when corrosion level is relatively high. Confinement was demonstrated to provide excellent means to conteract bond loss for corroded reinforcing steel bars. It was shown that unconfined specimens generally split at a small slip with a large crack width and result in splitting failure while confined specimens contribute to a small crack width and generally cause a pullout failure. The analysis results agree reasonably well with the experiments.
基金Project(51171011) supported by the National Natural Science Foundation of China
文摘The stress corrosion crack (SCC) susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique (SSRT), tensile with polarization and surface analysis technique. The curves of tf^Cl/tf^W -strain rate are divided into three regions: stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of εf^Cl/εf^W - strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy (SEM). SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The εf becomes the parameter to predict tf because the relationship between εf^Cl/εf^W and tf^Cl/tf^w is a straight line for AerMet 100.
基金Project(2017zzts005) supported by the Fundamental Research Funds for the Central Universities of Central South University
文摘Mg-Li alloy,as a superlight metallic engineering material,shows great potential in the fields of aerospace and militarydue to its high specific strength,better formability,and excellent electromagnetic shielding performance.The research process ofMg-Li alloys is reviewed and three main problems are pointed out.Aimed at the poor corrosion resistance of Mg-Li alloys,thecorrosion behavior is mainly summarized.The surface treatment technologies,including electroplating,electroless plating,plasmaspraying,molten salt replacement,conversion coating,anodizing,micro-arc oxidation,organic coating,and organic-inorganic hybridcoating,are introduced in detail.Finally,the future development of corrosion and protection of Mg?Li alloys is discussed.
基金Project(FRF-IDRY-20-013)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(51974014,52074020)supported by the National Natural Science Foundation of China。
文摘To describe the deformation and strength characteristics of the corroded rock-like specimens containing a single crack under uniaxial compression,a damage constitutive model combining hydro-chemical damage with coupling damage of micro-flaws and macro-cracks is proposed.Firstly,based on phenomenological theory,the damage variable of the rock-like specimens subjected to water environment erosion and chemical corrosion is obtained.Secondly,a coupled damage variable for cracked rock-like specimens is derived based on the Lemaitre strain equivalence hypothesis,which combines the Weibull statistical damage model for micro-flaws and the fracture mechanics model for a macro single crack.Then,considering the residual strength characteristics of the rock-like materials,the damage variable is modified by introducing the correction coefficient,and the damage constitutive model of the corroded rock-like specimens with a single crack under uniaxial compression is established.The model is verified by comparing the experimental stress−strain curves,and the results are in good agreement with those provided in the literature.Finally,the correction coefficient of the damage variable proposed in this paper is discussed.The damage constitutive model developed in this paper provides an effective method to describe the stress−strain relationship and residual strength characteristics of the corroded rock-like specimens with a single crack under uniaxial compression.
基金Project(215M623)supported by the Scientific and Technological Research Council of TurkeyProject(CBU-BAP 2015-130)supported by the Scientific Research Project Office of Manisa Celal Bayar University,Turkey
文摘Cold metal transfer(CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determined in terms of predicting the effect of welding process on the possible failures in their constructions caused by corrosive agents. The present study investigates the effect of heat input on mechanical properties and corrosion rate of AA5754-AA7075 joints welded by CMT using ER5356 filler wire. Pore formation was observed not only in the weld metal but also in the partially melted zone of AA7075 base metal due to the vaporization of zinc. Increased heat input caused over aging and zinc vaporization in AA7075 base metal, and grain coarsening in AA5754 base metal consequently decreased the tensile strength. The average tensile strength of AA7075-AA5754 joints varies between 235 and 240 MPa. The ductile fracture occurred at the AA5754 base metal side in all samples. Pitting was observed as the dominant corrosion mechanism. Corrosion resistance tended to increase with increasing heat input. Heat input values between 95 and 110 J/mm are recommended for the optimization of corrosion resistance and strength.
基金The National Natural Science Founda-tion of China(No.50508020)The National Basic Research Program(973)of China(No.2002CB412709)
文摘Considering the change of bond strength between corroded steel and concrete,flexural carrying ca- pacity of corroded reinforced concrete (RC) beam was calculated.On the basis of the condition of equilibrium of forces and compatibility of deformations for the whole beam,a model for the prediction of flexural carrying capacity of the corroded RC beam was proposed.Comparison of the model's predictions with the experimental results published in the literature shows the practicality of the proposed method.
文摘In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks' sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.
基金Project(N110607002)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(51074052)supported by the National Natural Science Foundation of China
文摘The effect of yield-to-tensile strength ratio(Y/T) on failure pressure of X70 pipeline without and with corrosion defects was investigated.The stress-strain response of materials was characterized by a power-law hardening curve.Two formulas to estimate the strain hardening exponent n for a special Y/T were obtained by least squared regression method and the influence of Y/T on n was analyzed.As an application of n-Y/T expression,the analytical solutions of burst pressure for X70 pipeline without and with corrosion defects were also obtained.The results indicate that the burst pressure of defect-free X70 pipe without corrosion defects is a function of the Y/T,pipe geometry t0/D0 and engineering tensile strength,and increases as Y/T or t0/D0 increases; whilst the burst pressure of corroded X70 pipe decreases with the increase of defect depths,d/t.Comparisons indicate that the present analytical solutions closely match available experimental and numerical data.
基金Project(2012CB619500) supported by the National Basic Research Program of ChinaProject(201012200238) supported from the Freedom Explore Program of Central South University, China
文摘The influence of exfoliation corrosion on the tensile properties of a high strength Al-Zn-Mg-Cu alloy was investigated by ambient temperature tensile testing, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). After exfoliation corrosion immersion, blisters and corrosion pits can be seen on the sheet surface, which lead to loss of materials and notches. A number of intergranular cracks are observed to initiate at the bottom of the corrosion-induced notches and propagate rapidly into the bulk materials during tensile. Consequently, exfoliation corrosion results in significant loss of strength and brittle fracture. EBSD results show that the crack propagation path is primarily along the grain boundaries with misorientation of-45°, and coincidence site lattice (CSL) boundaries are slightly more resistant to crack.
文摘The marine structures such as harbour,pier and inshore concrete terrace are exposed in adverse circumstances in a long period of time .Owing to the attack of external corrosive medium,their safety,durability and reliability decline.Especially the reinforced concrete(RC) structures in the wave splash area are more likely to be subjected to destruction and the loss is vast. Now the safety ,durability and reliability of structure have become increasingly an important subject to be studied.By way of the soaking and drying cycle test on the different mix proportions oblique section of 10 pieces of RC beams suffered artificial sea water(ASW) corrosion under 0,35,70,105,140 times of dry-wet cycles,the compared results of exerting pressure test of these beams under simply supporting were investigated. The law about the changes of the mechanical performance for RC beams with different mix proportions under different time periods for suffering corrosion of dry-wet cycles is as follows: the resistivity to ASW corrosion of the concrete specimens with various water cement ratio(various initial strength)is different;the characters of oblique section failure for RC beams attacked by sea water are about the same as those for ordinary RC beam; along with the extension of the time for sea water attack, the bearing capacity for oblique section of RC beams varies wave upon wave.The specimens attacked by sea water for about 35 times of corrosion cycle achieve minimum bearing capacity.
文摘Like reinforced concrete (RC) structure, Prestressed concrete (PC) structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems (staining, cracking and spalling of concrete). By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel (passive) and prestressing (active) reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.
基金supported by the National Key R&D Program of China(2017YFA0206904 and 2017YFA0206900)the National Natural Science Foundation of China(21625303,22122207,2190528721988102)。
文摘Osmotic energy between river water and seawater has attracted interest as a new source of sustainable energy.Nanofluidic membranes in a reverse electrodialysis configuration can capture energy from salinity gradients.However,current membrane materials suffer from high resistances,low stabilities,and low charge densities,which limit their further application.Here,we designed a high-performance nanofluidic membrane using carboxylic cellulose nanofibers functionalized with graphene oxide nanolamellas with cement-and-pebble microstructures and stable skeletons for enhanced ion transmembrane transport.By mixing artificial river water and seawater,the composite membrane achieved a high output power density up to 5.26 W m^(−2).Additionally,the membrane had an excellent acid resistance,which enabled long-term use with over 67 W m^(−2) of power density.The performance of this composite membrane benefited from the mechanically strong cellulose fibers and the bonding between nanofibers and nanolamellas.In this work,we highlight promising directions in industrial waste treatment using energy extracted from chemical potential gradients.