The intergranular cracking of 9% Ni cast steel seems mainly to relate to the segregation of contaminates H,S and P along boundaries.An addition of rare earth may eliminate the seg- regation of these contaminates along...The intergranular cracking of 9% Ni cast steel seems mainly to relate to the segregation of contaminates H,S and P along boundaries.An addition of rare earth may eliminate the seg- regation of these contaminates along grain boundaries and improve the binding force among boundaries,so as to reduce remarkably the intergranular cracking.展开更多
A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and...A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.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 specim...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 CO_(2) 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
In this study,we investigated the influence of hydrogen on the intergranular cracking and microdeformation mechanism in an equiatomic CoCrNi medium entropy alloy(MEA)fabricated via laser powder bed fusion(LPBF).The LP...In this study,we investigated the influence of hydrogen on the intergranular cracking and microdeformation mechanism in an equiatomic CoCrNi medium entropy alloy(MEA)fabricated via laser powder bed fusion(LPBF).The LPBF-built CoCrNi MEA was rather sensitive to hydrogen embrittlement,whose elongation deteriorated significantly when introducing hydrogen concurrently during deformation.The fracture mode also changed from ductile dimples to brittle fracture facets containing tear-ridge patterns.According to the electron backscatter diffraction(EBSD)measurements,the preferential propagation path of these brittle cracks was detected along grain boundaries,i.e.,intergranular(IG)fracture.In addition to the crack path,the IG crack morphological features and local plasticity evolutions were analyzed to characterize the hydrogen-induced IG cracking in LPBF-built material.More specifically,local grain refinement within the fusion boundaries resulted in a discontinuous IG crack morphology,including frequent crack coalescence and deflection,which should be responsible for forming tear-ridge patterns on IG fracture facets.Furthermore,the subgrain boundaries also significantly affected the IG cracking since they were made of dislocations,which could enrich local hydrogen concentration and promote IG crack propagation.As for micro-deformation mechanisms,hydrogen promoted the formation of stacking faults and deformation twins by reducing stacking fault energy.With ongoing hydrogen charging,the deformation twins were triggered along different planes simultaneously at the early stage of plastic deformation instead of exhibiting a sequential procedure from forming stacking faults,primary deformation twinning to secondary deformation twinning in the uncharged specimen.展开更多
In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequen...In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.展开更多
Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and...Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.展开更多
In order to study the effects of aging treatment on the intergranular corrosion（IGC） and stress corrosion cracking（SCC） of 7003 aluminum alloy（AA7003）, the intergranular corrosion test, electrochemical test and ...In order to study the effects of aging treatment on the intergranular corrosion（IGC） and stress corrosion cracking（SCC） of 7003 aluminum alloy（AA7003）, the intergranular corrosion test, electrochemical test and slow strain rate test（SSRT）, combined with optical microscopy（OM） and scanning electron microscopy（SEM） as well as transmission electron microscopy（TEM） observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged（PA） temper is the lowest, with double peak aged（DPA） the moderate, and retrogression and re-aging（RRA） the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones（PFZ） of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility（ISCC） of AA7003 for three tempers follows the order： ISCC（RRA）展开更多
Hydrogen could be enriched on grain boundaries by stress induction and other traps.The enriched hydrogen facilitated emission and movement of dislocations and lowered plastic work.Consequently,fracture occurred easily...Hydrogen could be enriched on grain boundaries by stress induction and other traps.The enriched hydrogen facilitated emission and movement of dislocations and lowered plastic work.Consequently,fracture occurred easily along grain boundary.A normalized threshold value of hydrogen-induced cracking (HIC) along grain boundary is given as (KIH/KIC)2=1-0.162×10-3 βHCc(H)GH/(2γs-γb-0.16×103∑β CiGi),where βH and βi are the enrichment factors of hydrogen and other elements on grain boundaries,respectively;Cc(H) is hydrogen concentration induced by stress;C,is the average concentration of an element in the steel;GH and Gi are factors of fracture work along grain boundary with hydrogen and other elements,and γs and γb are surface free energy and grain boundary energy of Fe.For tubular steel,the calculated KH/KIC is 0.23 while the determined value is 0.26.The theoretical threshold value is well consistent with the experimental one.展开更多
The grain boundary character distribution(GBCD) optimization and its effect on the intergranular stress corrosion cracking(IGSCC) resistance in a cold-rolled and subsequently annealed Fe-18 Cr-17 Mn-2 Mo-0.85 N high-n...The grain boundary character distribution(GBCD) optimization and its effect on the intergranular stress corrosion cracking(IGSCC) resistance in a cold-rolled and subsequently annealed Fe-18 Cr-17 Mn-2 Mo-0.85 N high-nitrogen nickel-free austenitic stainless steel were systematically explored.The results show that stacking faults and planar slip bands appearing at the right amount of deformation(lower than 10%) are beneficial cold-rolled microstructures to the GBCD optimization.The proportion of special boundaries gradually increases in the subsequent stages of recrystallization and grain growth,accompanying with the growth of twin-related domain in the experimental steel.In this way,the fraction of low ∑ coincidence site lattice(CSL) boundaries can reach as high as 82.85% for the specimen cold-rolled by 5% and then annealed at 1423 K for 72 h.After GBCD optimization,low ∑ CSL boundaries and the special triple junctions(J2,J3) of high proportion can greatly hinder the nitride precipitation along grain boundaries and enhance the capability for intergranular crack arrest,thus improving the IGSCC resistance of the experimental steel.展开更多
In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidat...In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load conditions.Interrupted tests were performed to observe the damage characteristics at crack tip.Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time.The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries.Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time.Based on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.展开更多
Metallurgical modeling of microalloying boron behavior in nickel-based superalloys during pre-weld heat treatment and welding has been systematically established. Non-equilibrium grain boundary resegregation is physic...Metallurgical modeling of microalloying boron behavior in nickel-based superalloys during pre-weld heat treatment and welding has been systematically established. Non-equilibrium grain boundary resegregation is physically coupled with non-equilibrium solidification of the weld pool for improved quantitative understanding of the imminent detriment of boron near the as-transformed grain boundary of the mushy zone and weldability. A strategic priority of the reduction in boron through low heat input and pre-weld heat treatment to suppress massive boride nucleation and grain boundary liquation are introduced.Both factors are capable of reducing the material response to boron-assisted intergranular liquation cracking at the high-energy sites of the grain-coarsened heat-affected zone( HAZ) beneath the surface and are of practical importance to provide robust integrity of joints. The synergistic self-repairment arterial crack network with the crystallographic substructure of the backfill enables amelioration of the HAZ crack resistance. The theoretical predictions are in satisfactory agreement with the phenomenological microanalysis, indirectly. This metallurgical modeling is also applicable to other high-temperature aerospace materials with similar metallurgical properties.展开更多
The study introduces the chemical composition, mechanical properties, physical properties and production processes of the Fe-23Mn-2Al-V austenitic steel. Investigations were made into the formation of cracks in the ho...The study introduces the chemical composition, mechanical properties, physical properties and production processes of the Fe-23Mn-2Al-V austenitic steel. Investigations were made into the formation of cracks in the hot-rolled Fe-23Mn-2Al-V steel plates,with optical microscopy （OM）,scanning electron microscopy （SEM） and energy dispersive spectrum （EDS）. The results have shown that intergranular oxidation in the reheating furnace is the main cause of the cracks on the surface of the hot-rolled steel plates. The surface cracking can be largely avoided by controlling the remaining oxygen content in the reheating furnace and improving continuous casting （ CC ） processes to increase the thickness of fine equiaxed grain layer of the steel slabs.展开更多
The acoustic emission(AE)characteristics from the fatigue crack propagation in SM50B-Zc steel were strongly affected by the environment me- dium.The AE feature from the fatigue process both in air and in 3.5% NaCl aqu...The acoustic emission(AE)characteristics from the fatigue crack propagation in SM50B-Zc steel were strongly affected by the environment me- dium.The AE feature from the fatigue process both in air and in 3.5% NaCl aqueous solution mani- fested a periodicity which indicated the fatigue ex- tension was discontinuous.The fatigue striation and secondary cracking were the main AE sources during the fatigue crack growth in air.In contrast, AE during the fatigue crack propagation in 3.5% NaCl solution was released from the intergranular fracture and quasicleavage cracking.展开更多
ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D p...ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.展开更多
文摘The intergranular cracking of 9% Ni cast steel seems mainly to relate to the segregation of contaminates H,S and P along boundaries.An addition of rare earth may eliminate the seg- regation of these contaminates along grain boundaries and improve the binding force among boundaries,so as to reduce remarkably the intergranular cracking.
基金supported by the NationalNatural Science Foundation of China (NSFC) under Grant 11872078,and Beijing Natural Science Foundation No.3222005.
文摘A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.
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 CO_(2) 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 CNPC Science and Technology Project“Research and Development of Corrosion Resistant Materials for Extreme Environments”(No.2023ZZ11-02)the National Natural Science Foundation of China(No.52101113)+1 种基金the CNPC Basic Research and Strategic Reserve Technology Research Fund Project(No.2022DQ03(2022Z-01))the Basic Research and Strategic Reserve Technology Research Fund Project of CNPC(No.2023DQ03-04).
文摘In this study,we investigated the influence of hydrogen on the intergranular cracking and microdeformation mechanism in an equiatomic CoCrNi medium entropy alloy(MEA)fabricated via laser powder bed fusion(LPBF).The LPBF-built CoCrNi MEA was rather sensitive to hydrogen embrittlement,whose elongation deteriorated significantly when introducing hydrogen concurrently during deformation.The fracture mode also changed from ductile dimples to brittle fracture facets containing tear-ridge patterns.According to the electron backscatter diffraction(EBSD)measurements,the preferential propagation path of these brittle cracks was detected along grain boundaries,i.e.,intergranular(IG)fracture.In addition to the crack path,the IG crack morphological features and local plasticity evolutions were analyzed to characterize the hydrogen-induced IG cracking in LPBF-built material.More specifically,local grain refinement within the fusion boundaries resulted in a discontinuous IG crack morphology,including frequent crack coalescence and deflection,which should be responsible for forming tear-ridge patterns on IG fracture facets.Furthermore,the subgrain boundaries also significantly affected the IG cracking since they were made of dislocations,which could enrich local hydrogen concentration and promote IG crack propagation.As for micro-deformation mechanisms,hydrogen promoted the formation of stacking faults and deformation twins by reducing stacking fault energy.With ongoing hydrogen charging,the deformation twins were triggered along different planes simultaneously at the early stage of plastic deformation instead of exhibiting a sequential procedure from forming stacking faults,primary deformation twinning to secondary deformation twinning in the uncharged specimen.
文摘In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.
文摘Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.
基金Funded by the National Natural Science Foundation of China(No.51371039)
文摘In order to study the effects of aging treatment on the intergranular corrosion（IGC） and stress corrosion cracking（SCC） of 7003 aluminum alloy（AA7003）, the intergranular corrosion test, electrochemical test and slow strain rate test（SSRT）, combined with optical microscopy（OM） and scanning electron microscopy（SEM） as well as transmission electron microscopy（TEM） observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged（PA） temper is the lowest, with double peak aged（DPA） the moderate, and retrogression and re-aging（RRA） the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones（PFZ） of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility（ISCC） of AA7003 for three tempers follows the order： ISCC（RRA）
基金Project supported by the National Natural Science Foundation of China and Shanghai Baoshan Iron and Steel Co.
文摘Hydrogen could be enriched on grain boundaries by stress induction and other traps.The enriched hydrogen facilitated emission and movement of dislocations and lowered plastic work.Consequently,fracture occurred easily along grain boundary.A normalized threshold value of hydrogen-induced cracking (HIC) along grain boundary is given as (KIH/KIC)2=1-0.162×10-3 βHCc(H)GH/(2γs-γb-0.16×103∑β CiGi),where βH and βi are the enrichment factors of hydrogen and other elements on grain boundaries,respectively;Cc(H) is hydrogen concentration induced by stress;C,is the average concentration of an element in the steel;GH and Gi are factors of fracture work along grain boundary with hydrogen and other elements,and γs and γb are surface free energy and grain boundary energy of Fe.For tubular steel,the calculated KH/KIC is 0.23 while the determined value is 0.26.The theoretical threshold value is well consistent with the experimental one.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51871048 and 52171108)the Fundamental Research Funds for the Central Universities(Grant Nos.N2002014 and N2202011)。
文摘The grain boundary character distribution(GBCD) optimization and its effect on the intergranular stress corrosion cracking(IGSCC) resistance in a cold-rolled and subsequently annealed Fe-18 Cr-17 Mn-2 Mo-0.85 N high-nitrogen nickel-free austenitic stainless steel were systematically explored.The results show that stacking faults and planar slip bands appearing at the right amount of deformation(lower than 10%) are beneficial cold-rolled microstructures to the GBCD optimization.The proportion of special boundaries gradually increases in the subsequent stages of recrystallization and grain growth,accompanying with the growth of twin-related domain in the experimental steel.In this way,the fraction of low ∑ coincidence site lattice(CSL) boundaries can reach as high as 82.85% for the specimen cold-rolled by 5% and then annealed at 1423 K for 72 h.After GBCD optimization,low ∑ CSL boundaries and the special triple junctions(J2,J3) of high proportion can greatly hinder the nitride precipitation along grain boundaries and enhance the capability for intergranular crack arrest,thus improving the IGSCC resistance of the experimental steel.
基金supported by the National Key R&D Program of China(No.2022YFF0609300)the National Major Science and Technology Projects of China(J2019-VI-0021-0137).
文摘In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load conditions.Interrupted tests were performed to observe the damage characteristics at crack tip.Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time.The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries.Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time.Based on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.
文摘Metallurgical modeling of microalloying boron behavior in nickel-based superalloys during pre-weld heat treatment and welding has been systematically established. Non-equilibrium grain boundary resegregation is physically coupled with non-equilibrium solidification of the weld pool for improved quantitative understanding of the imminent detriment of boron near the as-transformed grain boundary of the mushy zone and weldability. A strategic priority of the reduction in boron through low heat input and pre-weld heat treatment to suppress massive boride nucleation and grain boundary liquation are introduced.Both factors are capable of reducing the material response to boron-assisted intergranular liquation cracking at the high-energy sites of the grain-coarsened heat-affected zone( HAZ) beneath the surface and are of practical importance to provide robust integrity of joints. The synergistic self-repairment arterial crack network with the crystallographic substructure of the backfill enables amelioration of the HAZ crack resistance. The theoretical predictions are in satisfactory agreement with the phenomenological microanalysis, indirectly. This metallurgical modeling is also applicable to other high-temperature aerospace materials with similar metallurgical properties.
文摘The study introduces the chemical composition, mechanical properties, physical properties and production processes of the Fe-23Mn-2Al-V austenitic steel. Investigations were made into the formation of cracks in the hot-rolled Fe-23Mn-2Al-V steel plates,with optical microscopy （OM）,scanning electron microscopy （SEM） and energy dispersive spectrum （EDS）. The results have shown that intergranular oxidation in the reheating furnace is the main cause of the cracks on the surface of the hot-rolled steel plates. The surface cracking can be largely avoided by controlling the remaining oxygen content in the reheating furnace and improving continuous casting （ CC ） processes to increase the thickness of fine equiaxed grain layer of the steel slabs.
文摘The acoustic emission(AE)characteristics from the fatigue crack propagation in SM50B-Zc steel were strongly affected by the environment me- dium.The AE feature from the fatigue process both in air and in 3.5% NaCl aqueous solution mani- fested a periodicity which indicated the fatigue ex- tension was discontinuous.The fatigue striation and secondary cracking were the main AE sources during the fatigue crack growth in air.In contrast, AE during the fatigue crack propagation in 3.5% NaCl solution was released from the intergranular fracture and quasicleavage cracking.
文摘ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.
