Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy wa...Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.展开更多
Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil env...Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil environment. The SCC behavior of X80 pipeline steel under the magnetic field and sulfate-reducing bacteria(SRB) environment was investigated by immersion tests, electrochemical tests, and slow strain rate tensile(SSRT) tests. The results showed that the corrosion and SCC sensitivity of X80 steel decreased with increasing the magnetic field strength in the sterile environment. The SCC sensitivity was higher in the biotic environment inoculated with SRB, but it also decreased with increasing magnetic field strength, which was due to the magnetic field reduces microbial activity and promotes the formation of dense film layer. This work provided theoretical guidance on the prevention of SCC in pipeline steel under magnetic field and SRB coexistence.展开更多
Crack initiation stress and crack damage stress are two critical indices for assessing the fracture strength of rock mass.However,understanding the stress characteristics of crack initiation and damage under triaxial ...Crack initiation stress and crack damage stress are two critical indices for assessing the fracture strength of rock mass.However,understanding the stress characteristics of crack initiation and damage under triaxial compression remains still immature.To address this problem,by acoustic monitoring,i.e.ultrasonic wave transmission and acoustic emission(AE),the integrated triaxial compression experiments were carried out on granitic specimens.The crack initiation and damage stresses were determined by wave velocity,wave amplitude and AE methods,respectively.The discrepancy of stresses for crack initiation and damage identified by these methods were examined.Results showed that the confinement affected the peak stress and corresponding strain,and these two parameters increased with increasing confining pressure.The ultrasonic wave velocity and wave amplitude first increased and then remained relatively stable,and finally decreased with increasing axial compressive stress.The number of AE events stayed at a relatively low extent until axial stress approached the peak;after that,the AE accumulative counts skyrocketed to the maximum.It also shows that for a given confinement,the stresses for crack initiation and damage identified by the wave amplitude method were the smallest,followed those by AE method and wave velocity method.Moreover,the stresses for crack initiation and crack damage identified by these methods increased generally with confining pressures.However,the rate of increment of these two crack stresses decreased with increasing confining pressure.In addition,the slight decrease in these two crack stresses ratios was noticed with increasing confining pressure.The findings are helpful to understand the crack stresses of deep rocks,in terms of support of deep underground engineering.展开更多
Magnesium(Mg)alloys have been widely used in automobile,aviation,computer,and other fields due to their lightweight,high specific strength and stiffness,low pollution,and good electromagnetic shielding performance.How...Magnesium(Mg)alloys have been widely used in automobile,aviation,computer,and other fields due to their lightweight,high specific strength and stiffness,low pollution,and good electromagnetic shielding performance.However,the chemical stability of Mg alloys is poor,especially in the corrosive medium environment with high stress corrosion sensitivity,which causes sudden damage to structural components and restricts their application field.In recent years,owing to the increasing failure rate of engineering structures caused by stress corrosion of Mg alloys,it has become necessary to understand and pay more attention to the stress corrosion cracking(SCC)behavior of Mg alloys.In this paper,the SCC mechanisms and test methods of Mg alloys have been summarized.The recent research progress on SCC of Mg alloys has been reviewed from the aspects of alloying,preparation process,surface modification,corrosive medium,and strain rate.More importantly,future research trends in the field of SCC of Mg alloys have also been proposed.展开更多
Using the single crack solution and the regular solution of plane harmonic function, the problem of Saint_Venant bending of a cracked cylinder by a transverse force was reduced to solving two sets of integral equation...Using the single crack solution and the regular solution of plane harmonic function, the problem of Saint_Venant bending of a cracked cylinder by a transverse force was reduced to solving two sets of integral equations and its general solution was then obtained. Based on the obtained solution, a method to calculate the bending center and the stress intensity factors of the cracked cylinger whose cross_section is not thin_walled, but of small torsion rigidity is proposed. Some numerical examples are given.展开更多
Hydrogen was a key factor resulting in stress corrosion cracking (SCC) of X80 pipeline steel in Ku'erle soil simulated solution. In this article, the effect of hydrogen on the SCC susceptibility of X80 steel was in...Hydrogen was a key factor resulting in stress corrosion cracking (SCC) of X80 pipeline steel in Ku'erle soil simulated solution. In this article, the effect of hydrogen on the SCC susceptibility of X80 steel was investigated further by slow strain rate tensile test, the surface fractures were observed using scanning electron microscopy (SEM), and the fracture mechanism of SCC was discussed. The results indicate that hydrogen increases the SCC susceptibility. The SEM micrographs of hydrogen precharged samples presents a brittle quasi-cleavage feature, and pits facilitate the transgranular crack initiation. In the electrochemical impedance spectroscopy (EIS) measurement, the decreased polarization resistance and the pitting resistance of samples with hydrogen indicate that hydrogen increases the dissolution rate and deteriorates the pitting corrosion resistance. The potentiodynamic polarization curves present that hydrogen also accelerates the dissolution rate of the crack tip.展开更多
The effects of pre-deformation and strain rate on the stress corrosion cracking (SCC) behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension (S...The effects of pre-deformation and strain rate on the stress corrosion cracking (SCC) behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension (SSRT), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones (PFZ) become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.展开更多
Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensi...Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensile (SSRT) test. The SCC mechanism and the effect of HC03 were discussed with the aid of electrochemical techniques. It is indicated that X80 steel shows enhunced susceptibility to SCC with the concentration of HCO3 increasing from 0.15 to 1.00 mol/L, and the susceptibility can be evaluated in terms of current density at -0.2 V vs. SCE. The SCC behavior is controlled by the dissolution-based mechanism in these circumstances. Increasing the concentration of HCO3 not only increases the risk of rupture of passive films but also promotes the anodic dissolution of crack tips. Besides, little susceptibility to SCC is found in dilute solution containing 0.05 mol/L HCO3 for X80 steel. This can be attributed to the inhibited repassivation of passive films, manifesting as a more intensive dissolution in the non-crack tip areas than at the crack tips.展开更多
Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on spec...Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on specimens, which were pretreated under the following conditions for 168 hours: temperature, 60 ℃; pressure, 10 MPa; H2S partial pressure, 1 MPa and CO2 partial pressure, 1 MPa; preload stress, 80% of the yield strength (os); medium, simulated formation water. The reduction in tensile and impact strengths for P-110 casing specimens in corrosive environments were 28% and 54%, respectively. The surface morphology analysis indicated that surface damage and uniform plastic deformation occurred as a result of strain aging. Impact toughness of the casing decreased significantly and intergranular cracking occurred when specimens were maintained at a high stress level of 85% %.展开更多
The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 A1 alloy were inves- tigated in this paper. Devanthan-Stachurski (D-S) cell tests were used to measure the ...The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 A1 alloy were inves- tigated in this paper. Devanthan-Stachurski (D-S) cell tests were used to measure the apparent hydrogen diffusivity and hydrogen permeation current density of specimens immersed in 3.5wt% NaCl solution. Electrochemical experiment results show that the SCC susceptibility is low during anodic polarization. Both corrosion pits and hydrogen-induced cracking are evident in scanning electron microscope images after the specimens have been charging for 24 h.展开更多
Stress corrosion cracking (SCC) of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants (NPPs). The nitrogen-added ...Stress corrosion cracking (SCC) of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants (NPPs). The nitrogen-added stainless steel is a kind of possible candidate materials for mitigating SCC since reducing the carbon content and adding nitrogen to offset the loss in strength caused by the decrease in carbon content can mitigate the problem of sensitization. However, the reports of SCC of nitrogen-added stainless steels in high temperature water are few available. The effects of applied potential and sensitization treatment on the SCC of a newly developed nitrogen-containing stainless steel (SS) 316LN in high temperature water doped with chloride at 250 ℃ were studied by using slow strain rate tests (SSRTs). The SSRT results are compared with our data previously published for 316 SS without nitrogen and 304NG SS with nitrogen, and the possible mechanism affecting the SCC behaviors of the studied steels is also discussed based on SSRT and microstucture analysis results. The susceptibility to cracking of 316LN SS normally increases with increasing potential. The susceptibility to SCC of 316LN SS was less than that of 316 SS and 304NG SS. Sensitization treatment at 700℃ for 30 h showed little effect on the S CC of 316LN S S and significant effect on the S CC of 316 S S. The predominant cracking mode for the 316LN S S in both annealed state and the state after the sensitization treatment was transgranular. The presented conditions of mitigating stress corrosion cracking are some useful information for the safe use of 316LN SS in NPPs.展开更多
The environment-sensitive fracture behaviour of 0Cr18Ni9Ti austenitic stainless steel in boiling 42% MgCl_2 under the specific load of low frequency and high mean stress was inves- tigated from the relations and diffe...The environment-sensitive fracture behaviour of 0Cr18Ni9Ti austenitic stainless steel in boiling 42% MgCl_2 under the specific load of low frequency and high mean stress was inves- tigated from the relations and differences of crack growth rates and fractographs between stress corrosion fatigue and stress corrosion cracking.The interaction between stress corro- sion cracking and corrosion fatigue was also studied from fracture characteristics with empha- sis on the effects of applied potential on the interaction.展开更多
The stress corrosion cracking(SCC) behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test(SSRT) and SEM-EDS. The SCC susceptibility was estimated with the loss of...The stress corrosion cracking(SCC) behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test(SSRT) and SEM-EDS. The SCC susceptibility was estimated with the loss of the reduction in area. The experimental results indicate that the SCC susceptibility of 7A52 aluminum alloy in 3.5% chloride solution is the highest at strain rate of 1×10-6 s-1. The lowest one is under the condition of 1×10-5 s-1. Stress concentration and anode dissolving around Al-Fe-Mn intermetallics initiate micropores which will result in microcracks. The existence of intermetallics in the microstructure may play an important role in understanding the SCC initiation mechanisms of 7A52 aluminum alloy.展开更多
In order to investigate stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint area in acidic soil environ- ment in China, two simulating methods were used: one was to obtain bad microstructures i...In order to investigate stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint area in acidic soil environ- ment in China, two simulating methods were used: one was to obtain bad microstructures in heat affected zone by annealing at 1300 ℃ for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south- east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed using slow stain rate test (SSRT) and potentiodynamic polarization technique to investigate the SCC electrochemical mechanism of different microstructures further. The results show that SCC appears in the original microstructure and the quenched microstructure as the polarization potential decreases. Hydrogen revolution accelerates SCC of the two tested materials within the range of-850 mV to -1200 mV vs. SCE. Microstructural hardening and grain coarsening also increase SCC. The SCC mechanisms are different, anodic dissolution is the key of causing SCC as the polarization potential is higher than the null current potential, and hydrogen embrittlement will play a more important role to SCC as the polarization potential lower than the null current potential.展开更多
With the resistance to stress corrosion of the base metal as a reference, the contrast result of stress corrosion cracking ( SCC) susceptibility of aluminum-copper alloy 2219 and 2014 welded joints under different w...With the resistance to stress corrosion of the base metal as a reference, the contrast result of stress corrosion cracking ( SCC) susceptibility of aluminum-copper alloy 2219 and 2014 welded joints under different welding processes ( VP-TIG welding, HF-TIG hybrid welding, laser-TIG hybrid welding and laser HF-TIG hybrid welding) is obtained via the slow strain rate testing ( SSRT) , scanning electron microscope ( SEM) and microstructure observation auxiliary technologies. Test results show that the joints of aluminum alloy 2219, welded by hybrid welding processes, have superior resistance to stress corrosion compared to those welded by the VP-TIG welding process in varying degrees, especially, the joint welded by the laser HF-TIG hybrid welding process, where the resistance to stress corrosion is almost the same as that of the base material. However, the HF or laser hybrid welding effect is not significant under the same welding conditions for welded joints of aluminum alloy 2014.展开更多
In this paper, the dynamic behavior of a permeable crack in functionally graded piezoelectric/piezomagnetic materials is investigated. To make the analysis tractable, it is assumed that the material properties vary ex...In this paper, the dynamic behavior of a permeable crack in functionally graded piezoelectric/piezomagnetic materials is investigated. To make the analysis tractable, it is assumed that the material properties vary exponentially with the coordinate parallel to the crack. By using the Fourier transform, the problem can be solved with the help of a pair of dual integral equations in which the unknown is the jump of displacements across the crack surfaces. These equations are solved to obtain the relations between the electric filed, the magnetic flux field and the dynamic stress field near the crack tips using the Schmidt method. Numerical examples are provided to show the effect of the functionally graded parameter and the circular frequency of the incident waves upon the stress, the electric displacement and the magnetic flux intensity factors of the crack.展开更多
Through performing the tensile tests with different strain rates in 3.5 wt.%NaCl solution,the stress corrosion cracking(SCC)behavior and the effect of strain rate on the SCC susceptibility of an extruded Mg-7%Gd-5%Y-1...Through performing the tensile tests with different strain rates in 3.5 wt.%NaCl solution,the stress corrosion cracking(SCC)behavior and the effect of strain rate on the SCC susceptibility of an extruded Mg-7%Gd-5%Y-1%Nd-0.5%Zr(EW75)alloy have been investigated.Results demonstrate that the alloy is susceptible to SCC when the strain rate is lower than 5×10^(−6) s^(−1).At the strain rate of 1×10^(−6) s^(−1),the SCC susceptibility index(I_(SCC))is 0.96 and the elongation-to-failure(ε_(f))is only 0.11%.Fractography indicates that the brittle quasi-cleavage feature is very obvious and become more pronounced with decreasing the strain rate.Further analysis confirms that the cracking mode is predominantly transgranular,but the partial intergranular cracking at some localized area can also occur.Meanwhile,it seems that the crack propagation path is unrelated to the existing phase particles.展开更多
Slow strain rate testing (SSRT) was employed to study the stress corrosion cracking (SCC) behavior of ZE41 magnesium alloy in 0.01 M NaCl solution. Smooth tensile specimens with different thicknesses were strained...Slow strain rate testing (SSRT) was employed to study the stress corrosion cracking (SCC) behavior of ZE41 magnesium alloy in 0.01 M NaCl solution. Smooth tensile specimens with different thicknesses were strained dynamically in both longitudinal and transverse direction under permanent immersions at a strain rate of 10-6 s-1. It is found that ZE41 magnesium alloy is susceptible to SCC in 0.01 M NaCl solution. The SCC susceptibility of the thinner specimen is lower than that of the thicker specimen. Also, the longitudinal specimens are slightly more susceptible to SCC than the transverse specimens. The SCC mechanism of magnesium alloy is attributed to the combination of anodic dissolution with hydrogen embrittlement.展开更多
The fatigue pre-cracking 304 stainless steel (SS) specimens with lengths of 1.002 mm (L-crack) and 0.575 mm (S-crack) were prepared. Their corrosion behavior was studied by electrochemical noise (EN) in 4 mol/L NaCl +...The fatigue pre-cracking 304 stainless steel (SS) specimens with lengths of 1.002 mm (L-crack) and 0.575 mm (S-crack) were prepared. Their corrosion behavior was studied by electrochemical noise (EN) in 4 mol/L NaCl + 0.01 mol/L Na2S2O3 solution under slow-strain-rate-testing (SSRT) conditions. Moreover, the characteristics of L-crack's surface morphology and potential distribution with scanning Kelvin probe (SKP) before and after SSRT were also discussed. Compared with S-crack, L-crack is propagated and the features of crack propagation can be obtained. After propagation, the noise amplitudes increase with increasing stress and accelerating corrosion, the white noises at low and high frequencies (WL and WH) of the later stage are one order of magnitude larger than that at early stage in the current power spectral densities (PSDs). The potential PSDs also increase, but WH disappears. In addition, the crack propagation can be demonstrated according to variation of probability distribution, surface morphology and potential distribution.展开更多
This study aims at providing systematically insights to clarify the impact of cathodic polarization on the stress corrosion cracking(SCC)behavior of 21 Cr2 NiMo steel.Slow-strain-rate tensile tests demonstrated that 2...This study aims at providing systematically insights to clarify the impact of cathodic polarization on the stress corrosion cracking(SCC)behavior of 21 Cr2 NiMo steel.Slow-strain-rate tensile tests demonstrated that 21 Cr2 NiMo steel is highly sensitive to hydrogen embrittlement at strong cathodic polarization.The lowest SCC susceptibility occurred at-775 mV vs.SCE,whereas the SCC susceptibility was remarkably higher at potentials below-950 mV vs.SCE.Scanning electron microscopy(SEM)and electron backscattered diffraction(EBSD)revealed that the cathodic potential decline caused a transition from transgranular to intergranular mode in the fracture path.The intergranular mode transformed from bainite boundaries separation to prior austenitic grain boundaries separation under stronger cathodic polarization.Furthermore,corrosion pits promoted the nucleation of SCC cracks.In conclusion,with the decrease in the applied potential,the SCC mechanism transformed from the combination of hydrogen embrittlement and anodic dissolution to typical hydrogen embrittlement.展开更多
基金the National Natural Science Foundation of China Projects under Grant[Nos.51871211,U21A2049,52071220,51701129 and 51971054]Liaoning Province’s project of"Revitalizing Liaoning Talents"(XLYC1907062)+10 种基金the Doctor Startup Fund of Natural Science Foundation Program of Liaoning Province(No.2019-BS-200)the Strategic New Industry Development Special Foundation of Shenzhen(JCYJ20170306141749970)the funds of International Joint Laboratory for Light AlloysLiaoning Bai Qian Wan Talents Programthe Domain Foundation of Equipment Advance Research of 13th Five-year Plan(61409220118)National Key Research and Development Program of China under Grant[Nos.2017YFB0702001 and 2016YFB0301105]the Innovation Fund of Institute of Metal Research(IMR)Chinese Academy of Sciences(CAS)the National Basic Research Program of China(973 Program)project under Grant No.2013CB632205the Fundamental Research Fund for the Central Universities under Grant[No.N2009006]Bintech-IMR R&D Program[No.GYY-JSBU-2022-009]。
文摘Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.
基金supported by the National Science Foundation of China(Grant numbers 52274062)Natural Science Foundation of Liaoning Province(Grant numbers 2022-MS-362)。
文摘Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil environment. The SCC behavior of X80 pipeline steel under the magnetic field and sulfate-reducing bacteria(SRB) environment was investigated by immersion tests, electrochemical tests, and slow strain rate tensile(SSRT) tests. The results showed that the corrosion and SCC sensitivity of X80 steel decreased with increasing the magnetic field strength in the sterile environment. The SCC sensitivity was higher in the biotic environment inoculated with SRB, but it also decreased with increasing magnetic field strength, which was due to the magnetic field reduces microbial activity and promotes the formation of dense film layer. This work provided theoretical guidance on the prevention of SCC in pipeline steel under magnetic field and SRB coexistence.
基金funded by Shenzhen Basic Research Program,China(Grant No.JCYJ20220818095605012)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams,China(Grant No.2019ZT08G315)the National Science Foundation of China(Grant No.52121003).
文摘Crack initiation stress and crack damage stress are two critical indices for assessing the fracture strength of rock mass.However,understanding the stress characteristics of crack initiation and damage under triaxial compression remains still immature.To address this problem,by acoustic monitoring,i.e.ultrasonic wave transmission and acoustic emission(AE),the integrated triaxial compression experiments were carried out on granitic specimens.The crack initiation and damage stresses were determined by wave velocity,wave amplitude and AE methods,respectively.The discrepancy of stresses for crack initiation and damage identified by these methods were examined.Results showed that the confinement affected the peak stress and corresponding strain,and these two parameters increased with increasing confining pressure.The ultrasonic wave velocity and wave amplitude first increased and then remained relatively stable,and finally decreased with increasing axial compressive stress.The number of AE events stayed at a relatively low extent until axial stress approached the peak;after that,the AE accumulative counts skyrocketed to the maximum.It also shows that for a given confinement,the stresses for crack initiation and damage identified by the wave amplitude method were the smallest,followed those by AE method and wave velocity method.Moreover,the stresses for crack initiation and crack damage identified by these methods increased generally with confining pressures.However,the rate of increment of these two crack stresses decreased with increasing confining pressure.In addition,the slight decrease in these two crack stresses ratios was noticed with increasing confining pressure.The findings are helpful to understand the crack stresses of deep rocks,in terms of support of deep underground engineering.
基金supported by the National Natural Science Foundation of China(52071175)the Key Research&Development Plan(Social Development)of Jiangsu Province(BE2020702)。
文摘Magnesium(Mg)alloys have been widely used in automobile,aviation,computer,and other fields due to their lightweight,high specific strength and stiffness,low pollution,and good electromagnetic shielding performance.However,the chemical stability of Mg alloys is poor,especially in the corrosive medium environment with high stress corrosion sensitivity,which causes sudden damage to structural components and restricts their application field.In recent years,owing to the increasing failure rate of engineering structures caused by stress corrosion of Mg alloys,it has become necessary to understand and pay more attention to the stress corrosion cracking(SCC)behavior of Mg alloys.In this paper,the SCC mechanisms and test methods of Mg alloys have been summarized.The recent research progress on SCC of Mg alloys has been reviewed from the aspects of alloying,preparation process,surface modification,corrosive medium,and strain rate.More importantly,future research trends in the field of SCC of Mg alloys have also been proposed.
文摘Using the single crack solution and the regular solution of plane harmonic function, the problem of Saint_Venant bending of a cracked cylinder by a transverse force was reduced to solving two sets of integral equations and its general solution was then obtained. Based on the obtained solution, a method to calculate the bending center and the stress intensity factors of the cracked cylinger whose cross_section is not thin_walled, but of small torsion rigidity is proposed. Some numerical examples are given.
基金supported by the National Science & Technology Infrastructure Development Program of China(No.2005DKA10400)
文摘Hydrogen was a key factor resulting in stress corrosion cracking (SCC) of X80 pipeline steel in Ku'erle soil simulated solution. In this article, the effect of hydrogen on the SCC susceptibility of X80 steel was investigated further by slow strain rate tensile test, the surface fractures were observed using scanning electron microscopy (SEM), and the fracture mechanism of SCC was discussed. The results indicate that hydrogen increases the SCC susceptibility. The SEM micrographs of hydrogen precharged samples presents a brittle quasi-cleavage feature, and pits facilitate the transgranular crack initiation. In the electrochemical impedance spectroscopy (EIS) measurement, the decreased polarization resistance and the pitting resistance of samples with hydrogen indicate that hydrogen increases the dissolution rate and deteriorates the pitting corrosion resistance. The potentiodynamic polarization curves present that hydrogen also accelerates the dissolution rate of the crack tip.
基金financially supported by the State Key Fundamental Research Program of China (No. 2005CB623706)
文摘The effects of pre-deformation and strain rate on the stress corrosion cracking (SCC) behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension (SSRT), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones (PFZ) become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.
文摘Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensile (SSRT) test. The SCC mechanism and the effect of HC03 were discussed with the aid of electrochemical techniques. It is indicated that X80 steel shows enhunced susceptibility to SCC with the concentration of HCO3 increasing from 0.15 to 1.00 mol/L, and the susceptibility can be evaluated in terms of current density at -0.2 V vs. SCE. The SCC behavior is controlled by the dissolution-based mechanism in these circumstances. Increasing the concentration of HCO3 not only increases the risk of rupture of passive films but also promotes the anodic dissolution of crack tips. Besides, little susceptibility to SCC is found in dilute solution containing 0.05 mol/L HCO3 for X80 steel. This can be attributed to the inhibited repassivation of passive films, manifesting as a more intensive dissolution in the non-crack tip areas than at the crack tips.
基金support of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University in Chinathe National Natural Science Foundation of China (Grant No.51004084)
文摘Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on specimens, which were pretreated under the following conditions for 168 hours: temperature, 60 ℃; pressure, 10 MPa; H2S partial pressure, 1 MPa and CO2 partial pressure, 1 MPa; preload stress, 80% of the yield strength (os); medium, simulated formation water. The reduction in tensile and impact strengths for P-110 casing specimens in corrosive environments were 28% and 54%, respectively. The surface morphology analysis indicated that surface damage and uniform plastic deformation occurred as a result of strain aging. Impact toughness of the casing decreased significantly and intergranular cracking occurred when specimens were maintained at a high stress level of 85% %.
基金financially supported by the Natural Science Foundation of Jiangsu Province, China (No. BK20141292)the Foundation of Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences (No. MCKF201412)
文摘The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 A1 alloy were inves- tigated in this paper. Devanthan-Stachurski (D-S) cell tests were used to measure the apparent hydrogen diffusivity and hydrogen permeation current density of specimens immersed in 3.5wt% NaCl solution. Electrochemical experiment results show that the SCC susceptibility is low during anodic polarization. Both corrosion pits and hydrogen-induced cracking are evident in scanning electron microscope images after the specimens have been charging for 24 h.
基金supported by National Basic Research Program of China (973 Program, Grant No. 2006CB605005)Shanghai Municipal Committee of Science and Technology of china(Grant No. 005207019,Grant No. 08520708000)
文摘Stress corrosion cracking (SCC) of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants (NPPs). The nitrogen-added stainless steel is a kind of possible candidate materials for mitigating SCC since reducing the carbon content and adding nitrogen to offset the loss in strength caused by the decrease in carbon content can mitigate the problem of sensitization. However, the reports of SCC of nitrogen-added stainless steels in high temperature water are few available. The effects of applied potential and sensitization treatment on the SCC of a newly developed nitrogen-containing stainless steel (SS) 316LN in high temperature water doped with chloride at 250 ℃ were studied by using slow strain rate tests (SSRTs). The SSRT results are compared with our data previously published for 316 SS without nitrogen and 304NG SS with nitrogen, and the possible mechanism affecting the SCC behaviors of the studied steels is also discussed based on SSRT and microstucture analysis results. The susceptibility to cracking of 316LN SS normally increases with increasing potential. The susceptibility to SCC of 316LN SS was less than that of 316 SS and 304NG SS. Sensitization treatment at 700℃ for 30 h showed little effect on the S CC of 316LN S S and significant effect on the S CC of 316 S S. The predominant cracking mode for the 316LN S S in both annealed state and the state after the sensitization treatment was transgranular. The presented conditions of mitigating stress corrosion cracking are some useful information for the safe use of 316LN SS in NPPs.
文摘The environment-sensitive fracture behaviour of 0Cr18Ni9Ti austenitic stainless steel in boiling 42% MgCl_2 under the specific load of low frequency and high mean stress was inves- tigated from the relations and differences of crack growth rates and fractographs between stress corrosion fatigue and stress corrosion cracking.The interaction between stress corro- sion cracking and corrosion fatigue was also studied from fracture characteristics with empha- sis on the effects of applied potential on the interaction.
基金Funded by the National Natural Science Foundation of China (No. 50801066)
文摘The stress corrosion cracking(SCC) behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test(SSRT) and SEM-EDS. The SCC susceptibility was estimated with the loss of the reduction in area. The experimental results indicate that the SCC susceptibility of 7A52 aluminum alloy in 3.5% chloride solution is the highest at strain rate of 1×10-6 s-1. The lowest one is under the condition of 1×10-5 s-1. Stress concentration and anode dissolving around Al-Fe-Mn intermetallics initiate micropores which will result in microcracks. The existence of intermetallics in the microstructure may play an important role in understanding the SCC initiation mechanisms of 7A52 aluminum alloy.
基金supported by the National Science and Technology Infrastructure Platforms Construction Projects of China (No.2005DKA 10400)the Major Fund in the Tenth Five-Year Development Plan of China (No.50499333-08)
文摘In order to investigate stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint area in acidic soil environ- ment in China, two simulating methods were used: one was to obtain bad microstructures in heat affected zone by annealing at 1300 ℃ for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south- east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed using slow stain rate test (SSRT) and potentiodynamic polarization technique to investigate the SCC electrochemical mechanism of different microstructures further. The results show that SCC appears in the original microstructure and the quenched microstructure as the polarization potential decreases. Hydrogen revolution accelerates SCC of the two tested materials within the range of-850 mV to -1200 mV vs. SCE. Microstructural hardening and grain coarsening also increase SCC. The SCC mechanisms are different, anodic dissolution is the key of causing SCC as the polarization potential is higher than the null current potential, and hydrogen embrittlement will play a more important role to SCC as the polarization potential lower than the null current potential.
基金This work was supported by the National Natural Science Foundation of China (No. 50375005).
文摘With the resistance to stress corrosion of the base metal as a reference, the contrast result of stress corrosion cracking ( SCC) susceptibility of aluminum-copper alloy 2219 and 2014 welded joints under different welding processes ( VP-TIG welding, HF-TIG hybrid welding, laser-TIG hybrid welding and laser HF-TIG hybrid welding) is obtained via the slow strain rate testing ( SSRT) , scanning electron microscope ( SEM) and microstructure observation auxiliary technologies. Test results show that the joints of aluminum alloy 2219, welded by hybrid welding processes, have superior resistance to stress corrosion compared to those welded by the VP-TIG welding process in varying degrees, especially, the joint welded by the laser HF-TIG hybrid welding process, where the resistance to stress corrosion is almost the same as that of the base material. However, the HF or laser hybrid welding effect is not significant under the same welding conditions for welded joints of aluminum alloy 2014.
基金Project supported by the National Natural Science Foundation of China (Nos.90405016 and 10572044)the Special Research Fund for the Doctoral Program of Higher Education (No.2004021334)
文摘In this paper, the dynamic behavior of a permeable crack in functionally graded piezoelectric/piezomagnetic materials is investigated. To make the analysis tractable, it is assumed that the material properties vary exponentially with the coordinate parallel to the crack. By using the Fourier transform, the problem can be solved with the help of a pair of dual integral equations in which the unknown is the jump of displacements across the crack surfaces. These equations are solved to obtain the relations between the electric filed, the magnetic flux field and the dynamic stress field near the crack tips using the Schmidt method. Numerical examples are provided to show the effect of the functionally graded parameter and the circular frequency of the incident waves upon the stress, the electric displacement and the magnetic flux intensity factors of the crack.
基金This work was supported by the National Natural Science Foundation of China projects under Grant Nos.51171192,51271183 and 51301172,the National Basic Research Program of China(973 Program)project under Grant No.2013CB632205 and the Innovation Fund of Institute of Metal Research(IMR),Chinese Academy of Sciences(CAS).
文摘Through performing the tensile tests with different strain rates in 3.5 wt.%NaCl solution,the stress corrosion cracking(SCC)behavior and the effect of strain rate on the SCC susceptibility of an extruded Mg-7%Gd-5%Y-1%Nd-0.5%Zr(EW75)alloy have been investigated.Results demonstrate that the alloy is susceptible to SCC when the strain rate is lower than 5×10^(−6) s^(−1).At the strain rate of 1×10^(−6) s^(−1),the SCC susceptibility index(I_(SCC))is 0.96 and the elongation-to-failure(ε_(f))is only 0.11%.Fractography indicates that the brittle quasi-cleavage feature is very obvious and become more pronounced with decreasing the strain rate.Further analysis confirms that the cracking mode is predominantly transgranular,but the partial intergranular cracking at some localized area can also occur.Meanwhile,it seems that the crack propagation path is unrelated to the existing phase particles.
基金Funded by the National Natural Science Foundation of China (No.50771093)
文摘Slow strain rate testing (SSRT) was employed to study the stress corrosion cracking (SCC) behavior of ZE41 magnesium alloy in 0.01 M NaCl solution. Smooth tensile specimens with different thicknesses were strained dynamically in both longitudinal and transverse direction under permanent immersions at a strain rate of 10-6 s-1. It is found that ZE41 magnesium alloy is susceptible to SCC in 0.01 M NaCl solution. The SCC susceptibility of the thinner specimen is lower than that of the thicker specimen. Also, the longitudinal specimens are slightly more susceptible to SCC than the transverse specimens. The SCC mechanism of magnesium alloy is attributed to the combination of anodic dissolution with hydrogen embrittlement.
基金Project(2006CB605004) supported by the National Basic Research Program of China
文摘The fatigue pre-cracking 304 stainless steel (SS) specimens with lengths of 1.002 mm (L-crack) and 0.575 mm (S-crack) were prepared. Their corrosion behavior was studied by electrochemical noise (EN) in 4 mol/L NaCl + 0.01 mol/L Na2S2O3 solution under slow-strain-rate-testing (SSRT) conditions. Moreover, the characteristics of L-crack's surface morphology and potential distribution with scanning Kelvin probe (SKP) before and after SSRT were also discussed. Compared with S-crack, L-crack is propagated and the features of crack propagation can be obtained. After propagation, the noise amplitudes increase with increasing stress and accelerating corrosion, the white noises at low and high frequencies (WL and WH) of the later stage are one order of magnitude larger than that at early stage in the current power spectral densities (PSDs). The potential PSDs also increase, but WH disappears. In addition, the crack propagation can be demonstrated according to variation of probability distribution, surface morphology and potential distribution.
基金financially supported by the National Science and Technology Major Project,China(No.2017-Ⅶ0012-0109)。
文摘This study aims at providing systematically insights to clarify the impact of cathodic polarization on the stress corrosion cracking(SCC)behavior of 21 Cr2 NiMo steel.Slow-strain-rate tensile tests demonstrated that 21 Cr2 NiMo steel is highly sensitive to hydrogen embrittlement at strong cathodic polarization.The lowest SCC susceptibility occurred at-775 mV vs.SCE,whereas the SCC susceptibility was remarkably higher at potentials below-950 mV vs.SCE.Scanning electron microscopy(SEM)and electron backscattered diffraction(EBSD)revealed that the cathodic potential decline caused a transition from transgranular to intergranular mode in the fracture path.The intergranular mode transformed from bainite boundaries separation to prior austenitic grain boundaries separation under stronger cathodic polarization.Furthermore,corrosion pits promoted the nucleation of SCC cracks.In conclusion,with the decrease in the applied potential,the SCC mechanism transformed from the combination of hydrogen embrittlement and anodic dissolution to typical hydrogen embrittlement.