An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands...An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}<111>twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.展开更多
Accurate determination of rock mass parameters is essential for ensuring the accuracy of numericalsimulations. Displacement back-analysis is the most widely used method;however, the reliability of thecurrent approache...Accurate determination of rock mass parameters is essential for ensuring the accuracy of numericalsimulations. Displacement back-analysis is the most widely used method;however, the reliability of thecurrent approaches remains unsatisfactory. Therefore, in this paper, a multistage rock mass parameterback-analysis method, that considers the construction process and displacement losses is proposed andimplemented through the coupling of numerical simulation, auto-machine learning (AutoML), andmulti-objective optimization algorithms (MOOAs). First, a parametric modeling platform for mechanizedtwin tunnels is developed, generating a dataset through extensive numerical simulations. Next, theAutoML method is utilized to establish a surrogate model linking rock parameters and displacements.The tunnel construction process is divided into multiple stages, transforming the rock mass parameterback-analysis into a multi-objective optimization problem, for which multi-objective optimization algorithmsare introduced to obtain the rock mass parameters. The newly proposed rock mass parameterback-analysis method is validated in a mechanized twin tunnel project, and its accuracy and effectivenessare demonstrated. Compared with traditional single-stage back-analysis methods, the proposedmodel decreases the average absolute percentage error from 12.73% to 4.34%, significantly improving theaccuracy of the back-analysis. Moreover, although the accuracy of back analysis significantly increaseswith the number of construction stages considered, the back analysis time is acceptable. This studyprovides a new method for displacement back analysis that is efficient and accurate, thereby paving theway for precise parameter determination in numerical simulations.展开更多
The mechanical properties and deformation mechanism of a C-doped interstitial high-entropy alloy(i HEA)with a nominal composition of Fe_(49.5)Mn_(29.7)Co_(9.9)Cr_(9.9)C_(1)(at.%)were investigated.An excellent combinat...The mechanical properties and deformation mechanism of a C-doped interstitial high-entropy alloy(i HEA)with a nominal composition of Fe_(49.5)Mn_(29.7)Co_(9.9)Cr_(9.9)C_(1)(at.%)were investigated.An excellent combination of strength and ductility was obtained by cold rolling and annealing.The structure of the alloy is consisted of FCC matrix and randomly distributed Cr_(23)C_(6).For gaining a better understanding of deformation mechanism,EBSD and TEM were conducted to characterize the microstructure of tensile specimens interrupted at different strains.At low strain(2%),deformation is dominated by dislocations and their partial slip.With the strain increase to 20%,deformation-driven athermal phase transformation and dislocations slip are the main deformation mechanism.While at high strain of 35%before necking,deformation twins have been observed besides the HCP phase.The simultaneous effect of phase transformation(TRIP effect)and mechanical twins(TWIP effect)delay the shrinkage,and improve the tensile strength and plasticity.What's more,compared with the HEA without C addition,the yield strength of the C-doped i HEA has been improved,which can be attributed to the grain refinement strengthening and precipitation hardening.Together with the lattice friction and solid solution strengthening,the theoretical calculated values of yield strength match well with the experimental results.展开更多
The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault ene...The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault energy was raised with an average slope of 2 mJ/m2 per 1 wt% Cu.The Fe–20Mn–1.3C–3Cu steel exhibited superior tensile properties,with the ultimate tensile strength reached at 2.27 GPa and elongation up to 96.9% owing to the high strain hardening that occurred.To examine the mechanism of this high strain hardening,dislocation density determination by XRD was calculated.The dislocation density increased with the increasing strain,and the addition of Cu resulted in a decrease in the dislocation density.A comparison of the strain-hardening behavior of Fe–20Mn–1.3C and Fe–20Mn–1.3C–3Cu TWIP steels was made in terms of modified Crussard–Jaoul（C–J） analysis and microstructural observations.Especially at low strains,the contributions of all the relevant deformation mechanisms—slip,twinning,and dynamic strain aging—were quantitatively evaluated.The analysis revealed that the dislocation storage was the leading factor to the increase of the strain hardening,while dynamic strain aging was a minor contributor to strain hardening.Twinning,which interacted with the matrix,acted as an effective barrier to dislocation motion.展开更多
The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compare...The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.展开更多
AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scann...AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.展开更多
In the present study,the influence of solute atoms together with dislocations at {101^-2} twin boundary（TB） on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was systematically ...In the present study,the influence of solute atoms together with dislocations at {101^-2} twin boundary（TB） on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was systematically studied.The results show that a large number of {101^-2} twins disappear during recompression along the normal direction.Both the TB-dislocation interaction and TB-solute-dislocation interaction can greatly enhance the yield stress of the recompression along the normal direction（ND）.However,the solute segregation at {1012} TBs with an intensive interaction with 〈a〉 dislocations cannot further enhance the yield stress of ND recompression.The samples with TB-dislocation interaction show a similar working hardening performance with that subjected to a TB-solute-dislocation interaction.Both the TB-dislocation interaction and TB-solute-dislocation interaction greatly reduce the value of work hardening peaks during a detwinning predominant deformation.展开更多
The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investig...The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope （TEM）. The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.展开更多
Heterogeneous laminated structure(HLS)design offers new opportunities to enhance the mechanical performance of high-entropy alloys(HEAs)through synergistic effects from heterogeneity.However,it remains challenging to ...Heterogeneous laminated structure(HLS)design offers new opportunities to enhance the mechanical performance of high-entropy alloys(HEAs)through synergistic effects from heterogeneity.However,it remains challenging to introduce the HLS into HEAs via severe plastic deformation due to their strong work-hardening capacity.In this study,a specially designed multi-level HLS,characterized by alterna-tively stacked micro-grained soft CoCrFeNi layers and nanostructured ultra-hard Al_(0.3)CoCrFeNi layers con-taining a three-phase microstructure(composed of nanograined face-centered cubic matrix,(Al,Ni)-rich B2 precipitates,and Cr-richσprecipitates),is controllably introduced into FCC HEAs via a conventional thermo-mechanical processing involving hot-pressing,cold-rolling,and annealing.Meanwhile,thermo-mechanical processing induces Al element diffusion across the layer interface,resulting in the formation of an interfacial transition layer and the establishment of a strong interface bonding between the neigh-boring CoCrFeNi and Al_(0.3)CoCrFeNi layers.As a result,the multi-level HLSed CoCrFeNi/Al_(0.3)CoCrFeNi com-posite exhibits a yield strength as high as 1127±25.4 MPa while maintaining a large fracture elongation(up to(26.3±2.4)%).Such an excellent strength-ductility synergy surpasses that of most previously reported high-performance monolithic bulk CoCrFeNi and Al_(0.3)CoCrFeNi HEAs prepared through care-ful chemical composition optimization and/or thermo-mechanical processing.Strong hetero-deformation induced strengthening benefited from the apparent microstructural/microhardness difference and the strong interface bonding between the neighbouring CoCrFeNi and Al03CoCrFeNi layers,together with si-multaneous activation of multiple strain hardening mechanisms containing mechanical twinning,stack-ing faults and precipitation strengthening,is responsible for the excellent strength-ductility combination.This multi-level HLS and its fabrication strategy provide an enlightening way to develop strong and duc-tile HEAs and can also be applied to high-performance designs of other metallic materials.展开更多
Introduction of hard particles is considered an effective approach to improve alloy wear resistances.However,the wear resistances of Mg alloys could be deteriorated by increasing the hard particle content in many rese...Introduction of hard particles is considered an effective approach to improve alloy wear resistances.However,the wear resistances of Mg alloys could be deteriorated by increasing the hard particle content in many researches.To reveal the underlying negative effect of precipitate on the wear resistance,the wear behaviors of three AZ-Mg alloys(precipitate contents:AZ31:2.1%,AZ61:3.8%,AZ91:5.0%)at the axial loads of 3 and 15 N were investigated.The results indicated that although wear volume of the AZ-Mg alloys decreased with the increasing Mg_(17)Al_(12)content at 3 N(0.30→0.24→0.20μm^(3))and 15 N(1.04→0.88→0.85μm^(3)),the relative wear resistances of AZ61 and AZ91 to AZ31 decreased with increasing load(AZ61:1.25→1.17,AZ91:1.50→1.22)and the reduction was proportional to the precipitates content(AZ61:7%,AZ91:28%).That is because the wear volume of AZ-Mg was mainly attributed to micro-cutting,which was negatively correlated with the precipitate content and tribolayer hardness.However,the wear hardening ability of AZ-Mg alloys was weakened by precipitate for its inhibition on the formation of mechanical twins that the precursors for the tribolayer.Moreover,the inhibition of the precipitate on tribolayer could be amplified by the load,resulting in an increase in tribolayer hardness at 3 N(AZ31:0.94,AZ61:1.03,AZ91:1.10 GPa)but a decrease at 15 N(AZ31:1.77,AZ61:1.73,AZ91:1.62 GPa).Therefore,the formation of twin was inhibited by precipitates,which is detrimental to the wear resistance of Mg alloys.That means the wear resistance could be enhanced by promoting twin formation,which provides a new concept for the design of wear-resistant Mg alloys.展开更多
Microstructures and mechanical properties of the 25Mn twinning induced plasticity （TWIP） steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 100...Microstructures and mechanical properties of the 25Mn twinning induced plasticity （TWIP） steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 1000℃, the 25Mn steel showed excellent comprehensive mechanical properties, the tensile strength was about 640 MPa, the yield strength was higher than 255 MPa, and the elongation was above 82%. The microstructure was analyzed by optical microscopy （OM）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. Before deformation the microstructure was composed of austenitic matrix and annealing twins at room temperature; at the same time, a significant amount of annealing twins and stacking faults were observed by TEM. Mechanical twins played a dominant role in deformation and as a result the mechanical properties were found to be excellent.展开更多
Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting,and the homogenized forged billet was hot-rolled.The plastic deformation mechanism was investigated through tensile testi...Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting,and the homogenized forged billet was hot-rolled.The plastic deformation mechanism was investigated through tensile testing of the hot-rolled sample.Different characterization techniques such as scanning electron microscopy,transmission electron microscopy,electron backscattered diffraction,and X-ray diffraction were used to analyze the microstructural evolution of steel under different strain levels.The steel had a single austenite phase,which was stable during deformation.After hot rolling,annealing twins were observed in the microstructure of the steel.The steel showed an excellent combination of mechanical properties,like a tensile strength of 527 MPa,impact energy of 203 J at−196℃,and an elongation of 67%till fracture.At the initial deformation stage,the dislocations were generated within the austenite grains,entangled and accumulated at the grain boundaries and annealing twin boundaries.Annealing twins participated in plastic deformation and hindered the dislocation movement.As the deformation progressed,the dislocation slip was hindered and produced stress concentration,and the stacking faults evolved into mechanical twins,which released the stress concentration and delayed the necking.展开更多
Crystal growth is a complicated phase transition process.A perfect mechanism for practical crystal growth process has not been proposed and well recognized up till now.A model,i.e.screw dislocation model presented by ...Crystal growth is a complicated phase transition process.A perfect mechanism for practical crystal growth process has not been proposed and well recognized up till now.A model,i.e.screw dislocation model presented by F.C.Frank for imperfect crystal growth was adopted during early 1950’s.No systemic research on defects other than screw dislocation has been conducted during a quite long time. Since 1980’s,we have engaged systematically in the investigation of the defect mechanism of crystal growth,and our conclusion is that any defect providing step sources in the growing surface can make contribution to continuous crystal growth.These steps contain both complete(whole)steps and sub steps(incomplete steps).展开更多
基金financially supported by the National Natural Science Foundation of China(No.51821001)。
文摘An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}<111>twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.52090081,52079068)the State Key Laboratory of Hydroscience and Hydraulic Engineering(Grant No.2021-KY-04).
文摘Accurate determination of rock mass parameters is essential for ensuring the accuracy of numericalsimulations. Displacement back-analysis is the most widely used method;however, the reliability of thecurrent approaches remains unsatisfactory. Therefore, in this paper, a multistage rock mass parameterback-analysis method, that considers the construction process and displacement losses is proposed andimplemented through the coupling of numerical simulation, auto-machine learning (AutoML), andmulti-objective optimization algorithms (MOOAs). First, a parametric modeling platform for mechanizedtwin tunnels is developed, generating a dataset through extensive numerical simulations. Next, theAutoML method is utilized to establish a surrogate model linking rock parameters and displacements.The tunnel construction process is divided into multiple stages, transforming the rock mass parameterback-analysis into a multi-objective optimization problem, for which multi-objective optimization algorithmsare introduced to obtain the rock mass parameters. The newly proposed rock mass parameterback-analysis method is validated in a mechanized twin tunnel project, and its accuracy and effectivenessare demonstrated. Compared with traditional single-stage back-analysis methods, the proposedmodel decreases the average absolute percentage error from 12.73% to 4.34%, significantly improving theaccuracy of the back-analysis. Moreover, although the accuracy of back analysis significantly increaseswith the number of construction stages considered, the back analysis time is acceptable. This studyprovides a new method for displacement back analysis that is efficient and accurate, thereby paving theway for precise parameter determination in numerical simulations.
基金supported by the National Natural Science Foundation of China(Grant No.52004224)the Fundamental Research Funds for the Central Universities(D5000200031)China Postdoctoral Science Foundation(2020M683559)。
文摘The mechanical properties and deformation mechanism of a C-doped interstitial high-entropy alloy(i HEA)with a nominal composition of Fe_(49.5)Mn_(29.7)Co_(9.9)Cr_(9.9)C_(1)(at.%)were investigated.An excellent combination of strength and ductility was obtained by cold rolling and annealing.The structure of the alloy is consisted of FCC matrix and randomly distributed Cr_(23)C_(6).For gaining a better understanding of deformation mechanism,EBSD and TEM were conducted to characterize the microstructure of tensile specimens interrupted at different strains.At low strain(2%),deformation is dominated by dislocations and their partial slip.With the strain increase to 20%,deformation-driven athermal phase transformation and dislocations slip are the main deformation mechanism.While at high strain of 35%before necking,deformation twins have been observed besides the HCP phase.The simultaneous effect of phase transformation(TRIP effect)and mechanical twins(TWIP effect)delay the shrinkage,and improve the tensile strength and plasticity.What's more,compared with the HEA without C addition,the yield strength of the C-doped i HEA has been improved,which can be attributed to the grain refinement strengthening and precipitation hardening.Together with the lattice friction and solid solution strengthening,the theoretical calculated values of yield strength match well with the experimental results.
基金financially supported by the Major Project for Industry-University-Research of Fujian Province,China (No.2011H6012)the Natural Science Foundation of Fujian Province,China (No.2011J01292)the Key Project of Fujian Provincial Department of Science and Technology (No.2011H0001)
文摘The effects of Cu on stacking fault energy,dislocation slip,mechanical twinning,and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity（TWIP） steels were systematically investigated.The stacking fault energy was raised with an average slope of 2 mJ/m2 per 1 wt% Cu.The Fe–20Mn–1.3C–3Cu steel exhibited superior tensile properties,with the ultimate tensile strength reached at 2.27 GPa and elongation up to 96.9% owing to the high strain hardening that occurred.To examine the mechanism of this high strain hardening,dislocation density determination by XRD was calculated.The dislocation density increased with the increasing strain,and the addition of Cu resulted in a decrease in the dislocation density.A comparison of the strain-hardening behavior of Fe–20Mn–1.3C and Fe–20Mn–1.3C–3Cu TWIP steels was made in terms of modified Crussard–Jaoul（C–J） analysis and microstructural observations.Especially at low strains,the contributions of all the relevant deformation mechanisms—slip,twinning,and dynamic strain aging—were quantitatively evaluated.The analysis revealed that the dislocation storage was the leading factor to the increase of the strain hardening,while dynamic strain aging was a minor contributor to strain hardening.Twinning,which interacted with the matrix,acted as an effective barrier to dislocation motion.
基金Saeed Sadeghpour would like to thank Jane,Aatos Erkon säätiö(JAES),and Tiina ja Antti Herlinin säätiö(TAHS)for their financial support on Advanced Steels for Green Planet Project.The authors would also like to greatly thank the members of the“Formability Laboratory”and“Advanced Steels and Thermomechanically Processed Engineering Ma-terials Laboratory”for their help and support。
文摘The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.
基金financially supported by the National Natural Science Foundation of China(No.51401019)the China Postdoctoral Science Foundation(No.2014M550612)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-14-048A1 and FRF-TP-15-055A2)the Common Construction Project from Beijing Municipal Commission of Education(No.FRF-SD-13-005B)
文摘AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.
基金the financial support from the National Natural Science Foundation of China(Nos.51371203and 51571041)the National Key Basic Research Program of China(No.2013CB632204)
文摘In the present study,the influence of solute atoms together with dislocations at {101^-2} twin boundary（TB） on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was systematically studied.The results show that a large number of {101^-2} twins disappear during recompression along the normal direction.Both the TB-dislocation interaction and TB-solute-dislocation interaction can greatly enhance the yield stress of the recompression along the normal direction（ND）.However,the solute segregation at {1012} TBs with an intensive interaction with 〈a〉 dislocations cannot further enhance the yield stress of ND recompression.The samples with TB-dislocation interaction show a similar working hardening performance with that subjected to a TB-solute-dislocation interaction.Both the TB-dislocation interaction and TB-solute-dislocation interaction greatly reduce the value of work hardening peaks during a detwinning predominant deformation.
基金Funded by of Liaoning Science and Technology Bureau(No.2007221007)
文摘The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope （TEM）. The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.
基金supported by the National Natural Science Foundation of China(No.52361021)the Major Discipline Academic and Technical Leaders Training Program of Jiangxi Province(No.20232BCJ23001)+1 种基金the Jiangxi Provincial Natural Science Foundation(No.20232ACB214003)the Jiangxi Province Major Science&Technology Research&Development Project(No.20223AAG01009).
文摘Heterogeneous laminated structure(HLS)design offers new opportunities to enhance the mechanical performance of high-entropy alloys(HEAs)through synergistic effects from heterogeneity.However,it remains challenging to introduce the HLS into HEAs via severe plastic deformation due to their strong work-hardening capacity.In this study,a specially designed multi-level HLS,characterized by alterna-tively stacked micro-grained soft CoCrFeNi layers and nanostructured ultra-hard Al_(0.3)CoCrFeNi layers con-taining a three-phase microstructure(composed of nanograined face-centered cubic matrix,(Al,Ni)-rich B2 precipitates,and Cr-richσprecipitates),is controllably introduced into FCC HEAs via a conventional thermo-mechanical processing involving hot-pressing,cold-rolling,and annealing.Meanwhile,thermo-mechanical processing induces Al element diffusion across the layer interface,resulting in the formation of an interfacial transition layer and the establishment of a strong interface bonding between the neigh-boring CoCrFeNi and Al_(0.3)CoCrFeNi layers.As a result,the multi-level HLSed CoCrFeNi/Al_(0.3)CoCrFeNi com-posite exhibits a yield strength as high as 1127±25.4 MPa while maintaining a large fracture elongation(up to(26.3±2.4)%).Such an excellent strength-ductility synergy surpasses that of most previously reported high-performance monolithic bulk CoCrFeNi and Al_(0.3)CoCrFeNi HEAs prepared through care-ful chemical composition optimization and/or thermo-mechanical processing.Strong hetero-deformation induced strengthening benefited from the apparent microstructural/microhardness difference and the strong interface bonding between the neighbouring CoCrFeNi and Al03CoCrFeNi layers,together with si-multaneous activation of multiple strain hardening mechanisms containing mechanical twinning,stack-ing faults and precipitation strengthening,is responsible for the excellent strength-ductility combination.This multi-level HLS and its fabrication strategy provide an enlightening way to develop strong and duc-tile HEAs and can also be applied to high-performance designs of other metallic materials.
基金supported by the National Natural Science Foundation of China(No.52101084)the General Program of National Natural Science Foundation of China(NO.52075544)+2 种基金Key Research and Development Plan of Guang Dong(NO.2023B0909020002)Guangdong Basic and Applied Basic Research Foundation(NO.2023A1515011579and 2024A1515030004)the Open Fund Projects of Key Lab of Industrial Fluid Energy Conservation and Pollution Control(Ministry of Education),Qingdao University of Technology(NO.CK20240045).
文摘Introduction of hard particles is considered an effective approach to improve alloy wear resistances.However,the wear resistances of Mg alloys could be deteriorated by increasing the hard particle content in many researches.To reveal the underlying negative effect of precipitate on the wear resistance,the wear behaviors of three AZ-Mg alloys(precipitate contents:AZ31:2.1%,AZ61:3.8%,AZ91:5.0%)at the axial loads of 3 and 15 N were investigated.The results indicated that although wear volume of the AZ-Mg alloys decreased with the increasing Mg_(17)Al_(12)content at 3 N(0.30→0.24→0.20μm^(3))and 15 N(1.04→0.88→0.85μm^(3)),the relative wear resistances of AZ61 and AZ91 to AZ31 decreased with increasing load(AZ61:1.25→1.17,AZ91:1.50→1.22)and the reduction was proportional to the precipitates content(AZ61:7%,AZ91:28%).That is because the wear volume of AZ-Mg was mainly attributed to micro-cutting,which was negatively correlated with the precipitate content and tribolayer hardness.However,the wear hardening ability of AZ-Mg alloys was weakened by precipitate for its inhibition on the formation of mechanical twins that the precursors for the tribolayer.Moreover,the inhibition of the precipitate on tribolayer could be amplified by the load,resulting in an increase in tribolayer hardness at 3 N(AZ31:0.94,AZ61:1.03,AZ91:1.10 GPa)but a decrease at 15 N(AZ31:1.77,AZ61:1.73,AZ91:1.62 GPa).Therefore,the formation of twin was inhibited by precipitates,which is detrimental to the wear resistance of Mg alloys.That means the wear resistance could be enhanced by promoting twin formation,which provides a new concept for the design of wear-resistant Mg alloys.
基金the National Natural Science Foundation of China (No.50575022)the Specialized Research Foundation for the Doctoral Program of Higher Education of China (No.20040008024)the National High-Tech Research and Development Program of China (No.2008AA03E502)
文摘Microstructures and mechanical properties of the 25Mn twinning induced plasticity （TWIP） steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 1000℃, the 25Mn steel showed excellent comprehensive mechanical properties, the tensile strength was about 640 MPa, the yield strength was higher than 255 MPa, and the elongation was above 82%. The microstructure was analyzed by optical microscopy （OM）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. Before deformation the microstructure was composed of austenitic matrix and annealing twins at room temperature; at the same time, a significant amount of annealing twins and stacking faults were observed by TEM. Mechanical twins played a dominant role in deformation and as a result the mechanical properties were found to be excellent.
基金supported by the National Key Research and Development Program of China(No.2017YFB0304900).
文摘Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting,and the homogenized forged billet was hot-rolled.The plastic deformation mechanism was investigated through tensile testing of the hot-rolled sample.Different characterization techniques such as scanning electron microscopy,transmission electron microscopy,electron backscattered diffraction,and X-ray diffraction were used to analyze the microstructural evolution of steel under different strain levels.The steel had a single austenite phase,which was stable during deformation.After hot rolling,annealing twins were observed in the microstructure of the steel.The steel showed an excellent combination of mechanical properties,like a tensile strength of 527 MPa,impact energy of 203 J at−196℃,and an elongation of 67%till fracture.At the initial deformation stage,the dislocations were generated within the austenite grains,entangled and accumulated at the grain boundaries and annealing twin boundaries.Annealing twins participated in plastic deformation and hindered the dislocation movement.As the deformation progressed,the dislocation slip was hindered and produced stress concentration,and the stacking faults evolved into mechanical twins,which released the stress concentration and delayed the necking.
文摘Crystal growth is a complicated phase transition process.A perfect mechanism for practical crystal growth process has not been proposed and well recognized up till now.A model,i.e.screw dislocation model presented by F.C.Frank for imperfect crystal growth was adopted during early 1950’s.No systemic research on defects other than screw dislocation has been conducted during a quite long time. Since 1980’s,we have engaged systematically in the investigation of the defect mechanism of crystal growth,and our conclusion is that any defect providing step sources in the growing surface can make contribution to continuous crystal growth.These steps contain both complete(whole)steps and sub steps(incomplete steps).
