Lightweight,high-strength,and heat-resistant protective structures have consistently been crucial for applications in extreme environments,such as aerospace,semiconductors,and nuclear power industries.Multilayered TC4...Lightweight,high-strength,and heat-resistant protective structures have consistently been crucial for applications in extreme environments,such as aerospace,semiconductors,and nuclear power industries.Multilayered TC4/TB8 titanium(Ti)laminates,inspired by theheterostructures of natural biological shells,were fabricated using a hybrid diffusion bonding-hot rolling process followed by an aging treatment,resulting in an architected micro structure.The laminate achieves an ultra-high yield stress of 1020 MPa and proper uniform elongation of 4.2%at 500℃.The TB8 layers with high-density nano-precipitates and dislocations act as hard zone,contributing to high strength.The TC4 layers,with their bimodal structure consisting of coarse and fine grains characterized by equiaxed and lamellar structures,experience more plastic strain than the TB8 layers.The hetero deformation associated with the detwinning ofαgrains in the TC4 layer induces toughening at high temperatures.展开更多
The relatively insufficient knowledge of the deformation behavior has limited the wide application of the lightest structure material-Mg alloys.Among others,bending behavior is of great importance because it is unavoi...The relatively insufficient knowledge of the deformation behavior has limited the wide application of the lightest structure material-Mg alloys.Among others,bending behavior is of great importance because it is unavoidably involved in various forming processes,such as folding,stamping,etc.The hexagonal close-packed structure makes it even a strong texture-dependent behavior and even hard to capture and predict.In this regard,the bending behaviors are investigated in terms of both experiments and simulations in the current work.Bending samples with longitudinal directions inclined from the transverse direction by different angles have been prepared from an extruded AZ31 plate,respectively.The moment-curvature curves and strain distribution have been recorded in the four-point bending tests assisted with an in-situ digital image correlation(DIC)system.A crystal-plasticity-based bending-specific approach named EVPSC-BEND was applied to bridge the mechanical response to the microstructure evolution and underlying deformation mechanisms.The flow stress,texture,twin volume fraction,stress distribution,and strain distribution evolve differently from sample to sample,manifesting strong texture-dependent bending behaviors.The underlying mechanisms associated with this texture dependency,especially the occurrence of both twinning and detwinning during the monotonic bending,are carefully discussed.Besides,the simulation has been conducted to reveal the moment-inclination angle relation of the investigated AZ31 extruded plate in terms of the polar coordinate,which intuitively shows the texture-dependent behaviors.Specifically,the samples with longitudinal directions parallel to the extruded direction bear the biggest initial yielding moment.展开更多
Twins play an important role in the texture transition during annealing.In a cold rolled high rare earth content magnesium(Mg)alloys with{10–12}extension twins,{11–21}extension twins,{10–11}compression twins and{10...Twins play an important role in the texture transition during annealing.In a cold rolled high rare earth content magnesium(Mg)alloys with{10–12}extension twins,{11–21}extension twins,{10–11}compression twins and{10–11}-{10–12}double twins and frequent twin-twin interactions,quasi-in-situ electron backscatter diffraction method was used to observe the twin induced static recrystallization(SRX)and related effect on texture during annealing.The results show that basal component was consumed owing to the SRX occurred in basal oriented{10–12}twins and SRXed grains with several specific orientations show preferential grain growth.SRX widely operated in the{10–12}extension and{11–21}extension twins,but absent in most{10–11}compression and{10–11}-{10–12}double twins,which is different to traditional twin induced SRX.Most compression/double twins detwinned while only partial tension twins detwinned.Operation of{11–21}twins and resultant twin-twin interaction facilitate the formation of serrated twin boundaries,which can serve as nucleation sites.Activation of<c+a>dislocation and related dislocation interaction in high dislocation density areas promote the formation of new grain boundaries and related SRX.Profuse<c+a>dislocations in basal oriented twins release the strain accumulation in compression/double twins and thus result in the absence of SRX.The twin size difference,storage energy and dislocation-twin interaction commonly functioned to the detwinning during annealing.The near-coincide site lattice boundaries that show high mobility were considered to be the important contributor to the preferential grain growth of SRXed grains.展开更多
In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(N...In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(ND),are investigated via quasi-in situ electron backscatter diffraction,and the causes of the twinning and detwinning behavior are explained according to Schmid law,local strain coordination,and slip trajectories.It is found that the twins are first nucleated and grow at a compressive strain of 3%along the RD.In addition to the Schmid factor(SF),the strain coordination factor(m’)also influences the selection of the twin variants during the twinning process,resulting in the nucleation of twins with a low SF.During the second and third steps of the application of continuous compressive strains with magnitudes and directions of 3%RD+3%ND and 3%RD+3%ND+2.5%ND,detwinning occurs to different extents.The observation of the detwinning behavior reveals that the order in which multiple twins within the same grain undergo complete detwinning is related to Schmid law and the strain concentration,with a low SF and a high strain concentration promoting complete detwinning.The interaction between slip dislocations and twin boundaries in the deformed grains as well as the pinning of dislocations at the tips of the {1012} tensile twins with a special structure result in incomplete detwinning.Understanding the microstructural evolution and twinning behavior of magnesium alloys under different deformation geometries is important for the development of high-strength and high-toughness magnesium alloys.展开更多
In this work,the{10–12}tensile twins are introduced to improve the drawability of the AZ31 Mg alloy sheet.Concretely,the drawing depth is increased by 32%compared with the as-received sheet at 200℃.This is because{1...In this work,the{10–12}tensile twins are introduced to improve the drawability of the AZ31 Mg alloy sheet.Concretely,the drawing depth is increased by 32%compared with the as-received sheet at 200℃.This is because{10–12}tensile twins promote the occurrences of many deformation mechanisms during warm deep drawing,such as slips,detwinning,dynamic recrystallization(DRX)behaviors,etc.Further,based on the different stress states during deep drawing,these mechanisms and their competition relationships,as well as texture evolutions,are systematically studied.Combined with critical resolved shear stress(CRSS)and microstructure evolution,the global Schmid factor(GSF)obtained by quantizing stress states by stress tensor(σ)can accurately predict the activation trend of deformation mechanisms.It is found that the stress states have a reverse influence on the activation trend of the{10–12}twinning and detwinning.The change of stress states affects the competitive relationships between detwinning and DRX,and then affects the process and degree of DRX.The{10–12}tensile twins and large plane strain promote the activation of prismatic slips,and the larger plane strain also deflected the{10–12}twinning lattice.The{10–12}tensile twins and their induced deformation mechanisms can prominently weaken the basal texture and improve the drawability.展开更多
This paper aims to build a constitutive model intended to describe the thermomechanical behavior of shape memory alloys. This behavior presents many facets, among them we have considered the simple way of shape memory...This paper aims to build a constitutive model intended to describe the thermomechanical behavior of shape memory alloys. This behavior presents many facets, among them we have considered the simple way of shape memory, which is one of most important properties of shape memory alloys. Because of numerous stages of this effect, the subject was divided into three independent parts. For each part, we built the corresponding thermodynamic potential and we deduced the constitutive equations. To make this model workable, we have developed an algorithm. The simulation was performed using the NiTi as shape memory alloy.展开更多
Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) ...Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) and electronic backscatter diffraction (EBSD). The results reveal that the basal texture intensity of continuously bent and annealed (CBA) sample is drastically weakened. A large number of twins are induced on the concave surface by the 1st pass bending and the density of twins obviously declines during the 2nd pass bending owing to the occurrence of detwinning. Due to the asymmetric tension?compression strain states between the outer and inner regions during V-bending, twinning and detwinning are generated alternatively during the CB process. The Erichsen value is 5.2 mm which increases by 41% compared with that of as-received sample. This obvious improvement of formability can be attributed to the weakened basal texture, which leads to a smaller plastic strain ratio (r-value)together with a larger strain-hardening exponent (n-value).展开更多
Twinning and detwinning behavior,together with slip behavior,are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction(RD)after each interrupted mechanical test v...Twinning and detwinning behavior,together with slip behavior,are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction(RD)after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique.The results show that twinning firstly takes place under the compressive strain along the RD.With the increasing compressive strain,{1012}tensile twins firstly nucleate,then propagate,and finally thicken.While under a reversed tensile strain along the RD,detwinning occurs.No nucleation happens during detwinning.Thus,tensile twins can detwin at lower tensile strain,followed by thinning,shortening,and vanishing.Slips are also activated to accommodate the plastic deformation.In the matrix,prismatic slip can only dominate at relatively high strains.Otherwise,basal slip dominates.While in the twins,prismatic slip can activate at lower strains,which is ascribed to the texture reorientation.展开更多
Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their...Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their unloading behaviors were less investigated,especially for rare-earth(RE)Mg alloys.In the current work,the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling.In terms of the stress-strain curves,the inelastic strain,the chord modulus,and the active deformation mechanisms,the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized.The inelastic strains are generally larger under compressive Loading-Un Loading(L-UL)than under tensile L-UL,along the transverse direction(TD)than along the rolling direction(RD)under tensile L-UL,and along RD than along TD under compressive L-UL.The basal slip,twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets.展开更多
Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in...Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.展开更多
To investigate the relationship between macro-plastic behavior and meso-deformation mechanism of Mg alloy AZ31, the mathematical models for various deformation mechanisms of slip, twinning and detwinning are establish...To investigate the relationship between macro-plastic behavior and meso-deformation mechanism of Mg alloy AZ31, the mathematical models for various deformation mechanisms of slip, twinning and detwinning are established, respectively. Furthermore, in order to capture the Bauschinger effect under cyclic loading, the back stress is introduced into the three independent deformation mechanisms, respectively. Finally, using the above-mentioned model, a new cyclic plastic constitutive model based on the constitutive theory of crystal deformation for magnesium alloy is established. On this basis, the numerical simulation for AZ31 under cyclic loading with the axial strain amplitude of 1.2% is carried out in accordance with the aforementioned crystal plas- ticity theory associated with the representative volume element model. The comparison between the stress-strain curves obtained from the simulation and the experiments shows that the macro- scopic mechanical responses predicted using the proposed model are in good agreement with the experimental results. In particular, the unique characteristics of cyclic macro-plastic behavior observed in the experiments can be satisfactorily captured by the presented crystal plasticity model. At the mesoscale, these features are caused by the alternate occurrence of twinning and detwinning mechanisms. The further analysis of meso-plastic behavior shows that there are het- erogeneous distributions of twinning, stress-strain and stress triaxiality in polycrystal under cyclic loading.展开更多
The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratche...The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratchetting) and its physical nature were revealed. The experimental results demonstrate that the cast AZ91 Mg alloy behaviors tension-compression symmetry, because the dislocation slipping and twinning occur during both the tensile and compressive deformations;although the cast AZ91 alloy presents a certain pseudo-elastic behavior during unloading due to the detwinning, there is no obvious S-shaped asymmetric hysteresis loop like that of wrought Mg alloy in the cyclic tensile-compressive tests, and an obvious cyclic hardening is observed;moreover, the ratchetting of the cast AZ91 alloy presented in the cyclic stressing tests depends remarkably on the prescribed mean stress and stress amplitude, but slightly changes with the stress rate, and the evolution of responding peak/valley strain greatly differs from that of wrought Mg alloys and stainless steels. This work provides rich experimental data for establishing the constitutive model of cast Mg alloys.展开更多
Detwinning behavior of a pre-twinned magnesium alloy AZ31 at cryogenic temperature was investigated,also with a focus on the annealing hardening behavior of samples with different fractions of pre-twins.Pre-compressio...Detwinning behavior of a pre-twinned magnesium alloy AZ31 at cryogenic temperature was investigated,also with a focus on the annealing hardening behavior of samples with different fractions of pre-twins.Pre-compression along the transverse direction with strains of 1.7%,3.0%,and 6.0% was applied to generated[1012]twins.Mechanical behavior,microstructure,and texture evolution during subsequent tension were examined.Our results show that low temperature did not change the fact that detwinning still pre-dominated in the pre-twinned samples under reverse loading.However,a relatively harder migration of twin boundaries was found at cryogenic temperature.An annealing hardening of 27-40 MPa was observed in the pre-twinned samples,and such a hardening effect shows a close relation with the fraction of pre-twins or the level of pre-strains.The annealing hardening effect disappeared if the matrix was consumed by twins along with the increased pre-compression strains.The corresponding reasons for the annealing hardening behavior were discussed.展开更多
Deformation and texture evolution of AZ31 B magnesium（Mg） alloy sheet under uniaxial tension, compression, and reverse loading after different pre-strain（compression and tension） were investigated experimentally. ...Deformation and texture evolution of AZ31 B magnesium（Mg） alloy sheet under uniaxial tension, compression, and reverse loading after different pre-strain（compression and tension） were investigated experimentally. The results indicate that the pre-compressive strain remarkably affects the reverse tensile yield stress and the width of the detwinning-dominant stage during inverse tension process. Similar to stress–strain curve of the uniaxial compression, the curve of reverse tensile yield value also has ‘S＇ shape, and its minimum value is only 38 MPa. The relationship between pre-compressive strain and the width of detwinning-dominant stage presents a linear growth, and the greater the precompressive strain is, the smaller the strain hardening rate of the detwinning-slip-dominant stage is. Compared with the reverse tension under pre-compression, the influence of the pre-tension deformation on the deformation mechanism of subsequent compression is relatively simple. With the increase in pre-tension strain, the yield stress of the reverse loading is rising.展开更多
Twinning and detwinning are the important deformation modes in magnesium alloys during cyclic loading at room temperature. To analyze these two deformation mechanism, cyclic compression–tension experiments were perfo...Twinning and detwinning are the important deformation modes in magnesium alloys during cyclic loading at room temperature. To analyze these two deformation mechanism, cyclic compression–tension experiments were performed on Mg–3Al–1Zn rolled sheet along the rolling direction. In these tests, the microstructure evolutions of a series of grains during deformation were traced by using quasi in situ electron backscatter diffraction(EBSD). Important quantities like the Schmid factors of twinning system, the fraction of twinning during compression, and the fraction of twinning after reverse loading were calculated on the basis of measured quantities. The influence of Schmid factor of twinning variants on detwinning upon reverse loading was analyzed. Detwinning would prefer to proceed during reverse loading if the Schmid factor of twinning in the twinning area before reverse loading is sufficiently large.展开更多
Specimens with single-phase martensite, net-like γ/martensite mixed structure and lamella-likeγ/martensite mixed structure were designed to investigate the effect of the γ phase on the mechanical behavior and the d...Specimens with single-phase martensite, net-like γ/martensite mixed structure and lamella-likeγ/martensite mixed structure were designed to investigate the effect of the γ phase on the mechanical behavior and the detwinning of non-modulated(NM) martensitic variant in Ni-rich Ni-Mn-Ga alloys under uniaxial compression. It can be found the existence of the γ phase significantly enhances the compressive stresses, and the net-like γ phase specimen presents a higher value of compressive strain than that of the lamella-like γ phase specimen. Especially, the detwinning plateau of the lamella-like γ phase specimen is almost invisible due to the martensite colonies with low Schmid factors. Finally, according to the calculation of deformation gradient tensor, we found that the tensors along compression direction(εzz) of net-like γ phase/martensite mixed structure specimen and single-phase martensite specimen are lower than that of the specimen with lamella-like γ phase/martensite mixed structure, which well explained the detwinning strain for these specimens. The present study not only highlights the role ofγ phase on the mechanical behavior, but also provides more guidelines for the mechanical training of Ni-Mn-Ga shape memory alloys.展开更多
Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)...Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)medium-entropy alloy with an average lamellae thickness of∼20 nm embedded by thinner nanotwins was fabricated by severe cold rolling to achieve superior thermal stability.Compared with the conventional nanotwinned CrCoNi with nanotwins inside ultra-fined grains,the hier-archical nanolaminated-nanotwinned(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8) exhibits a significant annealing-induced hard-ening effect,i.e.,hardness increasing from∼250 HV in the original specimen to∼500 HV in the cold-rolled status and finally∼630 HV after annealing at 600℃for 1 h.Detailed microstructure characterizations reveal that the reduced dislocation density and formation of L1_(2)ordered domain are mainly responsible for such hardening effect,which is facilitated by the effectively suppressed coarsening with annealing temperature,i.e.,slow detwinning process and well-retained low-angle nanolamellar structure.The coarsening mechanisms from the cold-rolled nanolamellae to the fully recrystallized micro-equiaxed structures under the annealing temperatures ranging from 400 to 800℃ were also elucidated by atomic observations.展开更多
Molecular dynamics simulations are performed to investigate the deformation behavior of nanocrystalline Ni with pre-twin atom structure.The simulation sample is composed of four grains with average size 12 nm.The simu...Molecular dynamics simulations are performed to investigate the deformation behavior of nanocrystalline Ni with pre-twin atom structure.The simulation sample is composed of four grains with average size 12 nm.The simulation technique of isobaric-isothermal ensemble(NPT) with high pressure is applied to obtain a sample with two circle twins.Under uniaxial tensile and shear loading,as well as different detwinning deformation behaviors are observed.Under uniaxial tension the detwinning deformation is induced by the event of grain growth,and it is supported by local energy analysis.Under the shear loading the detwinning deformation is related to the loading rate.The results show that there may be a critical shear rate.As the shear rate is sufficiently high the circle twin is found to be failed;as the shear rate is less than that rate,the size of circle twin become smaller and gradually approach a constant value.Our simulation results are in good agreement with experiment observation.展开更多
Detwinning is an important plastic deformation mechanism that can significantly affect the mechanical properties of twin-structured metals.Although many detwinning mechanisms have been proposed for pure metals,it is u...Detwinning is an important plastic deformation mechanism that can significantly affect the mechanical properties of twin-structured metals.Although many detwinning mechanisms have been proposed for pure metals,it is unclear whether such a deformation model is valid for nanocrystalline alloys because of the lack of direct evidence.Here,the atomicscale detwinning deformation process of a nanocrystalline AuAg alloy with an average grain size of~15 nm was investigated in situ.The results show that there are three types of detwinning mechanisms in nanocrystalline AuAg alloys.The first type of detwinning results from grain boundary migration.The second type of detwinning occurs through combined layer-by-layer thinning and incoherent twin boundary migration.The last one occurs through incoherent twin boundary migration,which results from the collective motion of partial dislocations in an array.展开更多
基金financially supported by the Natural Science Foundation of Changsha,China(No.kq2402015)the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIP)(Nos.NRF-2021R1A2C3006662 and NRF-2022R1A5A1030054)supported by Brain Pool Program through the NRF of Korea,funded by the Ministry of Science and ICT(No.NRF-RS_(2)02300263999)
文摘Lightweight,high-strength,and heat-resistant protective structures have consistently been crucial for applications in extreme environments,such as aerospace,semiconductors,and nuclear power industries.Multilayered TC4/TB8 titanium(Ti)laminates,inspired by theheterostructures of natural biological shells,were fabricated using a hybrid diffusion bonding-hot rolling process followed by an aging treatment,resulting in an architected micro structure.The laminate achieves an ultra-high yield stress of 1020 MPa and proper uniform elongation of 4.2%at 500℃.The TB8 layers with high-density nano-precipitates and dislocations act as hard zone,contributing to high strength.The TC4 layers,with their bimodal structure consisting of coarse and fine grains characterized by equiaxed and lamellar structures,experience more plastic strain than the TB8 layers.The hetero deformation associated with the detwinning ofαgrains in the TC4 layer induces toughening at high temperatures.
基金supported by State Key Laboratory for Geo Mechanics and Deep Underground Engineering,China University of Mining&Technology,Beijing(XD2021021)the National Natural Science Foundation of China(Nos.52075325,51975365,and 52011540403)。
文摘The relatively insufficient knowledge of the deformation behavior has limited the wide application of the lightest structure material-Mg alloys.Among others,bending behavior is of great importance because it is unavoidably involved in various forming processes,such as folding,stamping,etc.The hexagonal close-packed structure makes it even a strong texture-dependent behavior and even hard to capture and predict.In this regard,the bending behaviors are investigated in terms of both experiments and simulations in the current work.Bending samples with longitudinal directions inclined from the transverse direction by different angles have been prepared from an extruded AZ31 plate,respectively.The moment-curvature curves and strain distribution have been recorded in the four-point bending tests assisted with an in-situ digital image correlation(DIC)system.A crystal-plasticity-based bending-specific approach named EVPSC-BEND was applied to bridge the mechanical response to the microstructure evolution and underlying deformation mechanisms.The flow stress,texture,twin volume fraction,stress distribution,and strain distribution evolve differently from sample to sample,manifesting strong texture-dependent bending behaviors.The underlying mechanisms associated with this texture dependency,especially the occurrence of both twinning and detwinning during the monotonic bending,are carefully discussed.Besides,the simulation has been conducted to reveal the moment-inclination angle relation of the investigated AZ31 extruded plate in terms of the polar coordinate,which intuitively shows the texture-dependent behaviors.Specifically,the samples with longitudinal directions parallel to the extruded direction bear the biggest initial yielding moment.
基金supported by the National Natural Science Foundation of China(Nos.52301164,52371121 and 52271107).
文摘Twins play an important role in the texture transition during annealing.In a cold rolled high rare earth content magnesium(Mg)alloys with{10–12}extension twins,{11–21}extension twins,{10–11}compression twins and{10–11}-{10–12}double twins and frequent twin-twin interactions,quasi-in-situ electron backscatter diffraction method was used to observe the twin induced static recrystallization(SRX)and related effect on texture during annealing.The results show that basal component was consumed owing to the SRX occurred in basal oriented{10–12}twins and SRXed grains with several specific orientations show preferential grain growth.SRX widely operated in the{10–12}extension and{11–21}extension twins,but absent in most{10–11}compression and{10–11}-{10–12}double twins,which is different to traditional twin induced SRX.Most compression/double twins detwinned while only partial tension twins detwinned.Operation of{11–21}twins and resultant twin-twin interaction facilitate the formation of serrated twin boundaries,which can serve as nucleation sites.Activation of<c+a>dislocation and related dislocation interaction in high dislocation density areas promote the formation of new grain boundaries and related SRX.Profuse<c+a>dislocations in basal oriented twins release the strain accumulation in compression/double twins and thus result in the absence of SRX.The twin size difference,storage energy and dislocation-twin interaction commonly functioned to the detwinning during annealing.The near-coincide site lattice boundaries that show high mobility were considered to be the important contributor to the preferential grain growth of SRXed grains.
基金supported by the General Project of Liaoning Provincial Department of Education(NO:JYTMS20231199)Project of Liaoning Education Department(No:LKMZ20220462 and No:LJKMZ20220467)+1 种基金Basic scientific research project of Liaoning Provincial Department of Education(key research project)(No:JYTZD2023108)Liaoning Nature Fund Guidance Plan(No:42022-BS.179)。
文摘In this study,the twinning-detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction(RD)and normal direction(ND),are investigated via quasi-in situ electron backscatter diffraction,and the causes of the twinning and detwinning behavior are explained according to Schmid law,local strain coordination,and slip trajectories.It is found that the twins are first nucleated and grow at a compressive strain of 3%along the RD.In addition to the Schmid factor(SF),the strain coordination factor(m’)also influences the selection of the twin variants during the twinning process,resulting in the nucleation of twins with a low SF.During the second and third steps of the application of continuous compressive strains with magnitudes and directions of 3%RD+3%ND and 3%RD+3%ND+2.5%ND,detwinning occurs to different extents.The observation of the detwinning behavior reveals that the order in which multiple twins within the same grain undergo complete detwinning is related to Schmid law and the strain concentration,with a low SF and a high strain concentration promoting complete detwinning.The interaction between slip dislocations and twin boundaries in the deformed grains as well as the pinning of dislocations at the tips of the {1012} tensile twins with a special structure result in incomplete detwinning.Understanding the microstructural evolution and twinning behavior of magnesium alloys under different deformation geometries is important for the development of high-strength and high-toughness magnesium alloys.
基金supported by the National Natural Science Foundations of China[No.52374395,52474419]Natural Science Foundation of Chongqing[CSTB2024NSCQMSX0267]+6 种基金the Natural Science Foundation of Shanxi province[No.20210302123135,20210302123163]the China Postdoctoral Science Foundation[No.2022M710541]the Research Project Supported by Shanxi Scholarship Council of China[No.2022-038]Scientific and Technological Achievements Transformation Guidance Special Project of Shanxi Province[202104021301022,202204021301009]the Ministry of Science and Higher Education of the Russian Federation for financial support under the Megagrant[no.075-15-2022-1133]he National Research Foundation(NRF)grant funded by the Ministry of Science and ICT[2015R1A2A1A01006795]Korea through the Research Institute of Advanced Materials.
文摘In this work,the{10–12}tensile twins are introduced to improve the drawability of the AZ31 Mg alloy sheet.Concretely,the drawing depth is increased by 32%compared with the as-received sheet at 200℃.This is because{10–12}tensile twins promote the occurrences of many deformation mechanisms during warm deep drawing,such as slips,detwinning,dynamic recrystallization(DRX)behaviors,etc.Further,based on the different stress states during deep drawing,these mechanisms and their competition relationships,as well as texture evolutions,are systematically studied.Combined with critical resolved shear stress(CRSS)and microstructure evolution,the global Schmid factor(GSF)obtained by quantizing stress states by stress tensor(σ)can accurately predict the activation trend of deformation mechanisms.It is found that the stress states have a reverse influence on the activation trend of the{10–12}twinning and detwinning.The change of stress states affects the competitive relationships between detwinning and DRX,and then affects the process and degree of DRX.The{10–12}tensile twins and large plane strain promote the activation of prismatic slips,and the larger plane strain also deflected the{10–12}twinning lattice.The{10–12}tensile twins and their induced deformation mechanisms can prominently weaken the basal texture and improve the drawability.
文摘This paper aims to build a constitutive model intended to describe the thermomechanical behavior of shape memory alloys. This behavior presents many facets, among them we have considered the simple way of shape memory, which is one of most important properties of shape memory alloys. Because of numerous stages of this effect, the subject was divided into three independent parts. For each part, we built the corresponding thermodynamic potential and we deduced the constitutive equations. To make this model workable, we have developed an algorithm. The simulation was performed using the NiTi as shape memory alloy.
基金Project(CDJZR13130081)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(CSCT2014FAZKTJCSF50004)supported by the Chongqing Science and Technology Commission,China
文摘Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) and electronic backscatter diffraction (EBSD). The results reveal that the basal texture intensity of continuously bent and annealed (CBA) sample is drastically weakened. A large number of twins are induced on the concave surface by the 1st pass bending and the density of twins obviously declines during the 2nd pass bending owing to the occurrence of detwinning. Due to the asymmetric tension?compression strain states between the outer and inner regions during V-bending, twinning and detwinning are generated alternatively during the CB process. The Erichsen value is 5.2 mm which increases by 41% compared with that of as-received sample. This obvious improvement of formability can be attributed to the weakened basal texture, which leads to a smaller plastic strain ratio (r-value)together with a larger strain-hardening exponent (n-value).
基金support from the US Department of Energy,Office of Basic Energy Science under Award no.DE-SC0016333.
文摘Twinning and detwinning behavior,together with slip behavior,are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction(RD)after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique.The results show that twinning firstly takes place under the compressive strain along the RD.With the increasing compressive strain,{1012}tensile twins firstly nucleate,then propagate,and finally thicken.While under a reversed tensile strain along the RD,detwinning occurs.No nucleation happens during detwinning.Thus,tensile twins can detwin at lower tensile strain,followed by thinning,shortening,and vanishing.Slips are also activated to accommodate the plastic deformation.In the matrix,prismatic slip can only dominate at relatively high strains.Otherwise,basal slip dominates.While in the twins,prismatic slip can activate at lower strains,which is ascribed to the texture reorientation.
基金the support of the National Natural Science Foundation of China(Nos.51775337,51675331,51975365)Major Projects of the Ministry of Education(No.311017)+5 种基金the Program of Introducing Talents of Discipline to Universities(Grant No.B06012)sponsored by the Shanghai Pujiang Program(18PJ1405000)the University of Sydney-Shanghai Jiao Tong University Partnership Collaboration Awardssupported by the Natural Sciences and Engineering Research Council of Canada(Nos.RGPIN-201606464)partly supported by the Materials Genome Initiative Center,Shanghai Jiao Tong UniversityThe University of Michigan and Shanghai Jiao Tong University(UM-SJTU)joint research project(AE604401)。
文摘Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their unloading behaviors were less investigated,especially for rare-earth(RE)Mg alloys.In the current work,the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling.In terms of the stress-strain curves,the inelastic strain,the chord modulus,and the active deformation mechanisms,the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized.The inelastic strains are generally larger under compressive Loading-Un Loading(L-UL)than under tensile L-UL,along the transverse direction(TD)than along the rolling direction(RD)under tensile L-UL,and along RD than along TD under compressive L-UL.The basal slip,twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets.
基金financially supported by the Elements Strategy Initiative for Structural Materials (ESISM, grant No. JPMXP0112101000) in Kyoto UniversityRXZ was supported by National Natural Science Foundation of China (NSFC, No. 51901007)+1 种基金SH and KA were supported by JSPS KAKENHI Nos. JP18H05479 and JP18H05476The neutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed under a project program (Project No. 2014P0102)。
文摘Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.
基金Project （11462002） supported by the National Natural Science Foundation of China Project （2016GXNSFAA380218） supported by Guangxi Natural Science Foundation, China+1 种基金 Project （2014ZDK002） supported by the Open Project of Guangxi Key Laboratory of Disaster Prevention and Structural Safety at Guangxi University, China and Project （Z01） supported by the Science Foundation for Doctorate Research of Guangxi University of Science and Technology, China.
文摘To investigate the relationship between macro-plastic behavior and meso-deformation mechanism of Mg alloy AZ31, the mathematical models for various deformation mechanisms of slip, twinning and detwinning are established, respectively. Furthermore, in order to capture the Bauschinger effect under cyclic loading, the back stress is introduced into the three independent deformation mechanisms, respectively. Finally, using the above-mentioned model, a new cyclic plastic constitutive model based on the constitutive theory of crystal deformation for magnesium alloy is established. On this basis, the numerical simulation for AZ31 under cyclic loading with the axial strain amplitude of 1.2% is carried out in accordance with the aforementioned crystal plas- ticity theory associated with the representative volume element model. The comparison between the stress-strain curves obtained from the simulation and the experiments shows that the macro- scopic mechanical responses predicted using the proposed model are in good agreement with the experimental results. In particular, the unique characteristics of cyclic macro-plastic behavior observed in the experiments can be satisfactorily captured by the presented crystal plasticity model. At the mesoscale, these features are caused by the alternate occurrence of twinning and detwinning mechanisms. The further analysis of meso-plastic behavior shows that there are het- erogeneous distributions of twinning, stress-strain and stress triaxiality in polycrystal under cyclic loading.
基金Financial support from National Natural Science Foundation of China (11532010)。
文摘The uniaxial cyclic plasticity of cast AZ91 magnesium(Mg) alloy was investigated by conducting a series of cyclic straining and stressing tests at room temperature, and a unique cyclic plasticity(especially for ratchetting) and its physical nature were revealed. The experimental results demonstrate that the cast AZ91 Mg alloy behaviors tension-compression symmetry, because the dislocation slipping and twinning occur during both the tensile and compressive deformations;although the cast AZ91 alloy presents a certain pseudo-elastic behavior during unloading due to the detwinning, there is no obvious S-shaped asymmetric hysteresis loop like that of wrought Mg alloy in the cyclic tensile-compressive tests, and an obvious cyclic hardening is observed;moreover, the ratchetting of the cast AZ91 alloy presented in the cyclic stressing tests depends remarkably on the prescribed mean stress and stress amplitude, but slightly changes with the stress rate, and the evolution of responding peak/valley strain greatly differs from that of wrought Mg alloys and stainless steels. This work provides rich experimental data for establishing the constitutive model of cast Mg alloys.
基金co-supported by the National Natural Science Foundation of China(Nos.51901202 and 52101132)the Young Elite Scientist Sponsorship Program by CAST(YESS20230412)+4 种基金the China Postdoctoral Science Foundation(2022M713366)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology(ASMA202206)the Guangdong Basic and Applied Basic Research Foundation(2023A1515010075)the Natural Science Foundation of Jiangsu Province(No.BK 20191442)the Basic and Applied Basic Research Project of Guangzhou(202201011250).
文摘Detwinning behavior of a pre-twinned magnesium alloy AZ31 at cryogenic temperature was investigated,also with a focus on the annealing hardening behavior of samples with different fractions of pre-twins.Pre-compression along the transverse direction with strains of 1.7%,3.0%,and 6.0% was applied to generated[1012]twins.Mechanical behavior,microstructure,and texture evolution during subsequent tension were examined.Our results show that low temperature did not change the fact that detwinning still pre-dominated in the pre-twinned samples under reverse loading.However,a relatively harder migration of twin boundaries was found at cryogenic temperature.An annealing hardening of 27-40 MPa was observed in the pre-twinned samples,and such a hardening effect shows a close relation with the fraction of pre-twins or the level of pre-strains.The annealing hardening effect disappeared if the matrix was consumed by twins along with the increased pre-compression strains.The corresponding reasons for the annealing hardening behavior were discussed.
基金supported by the National Nature Science Foundation of China (No. 51174189)
文摘Deformation and texture evolution of AZ31 B magnesium（Mg） alloy sheet under uniaxial tension, compression, and reverse loading after different pre-strain（compression and tension） were investigated experimentally. The results indicate that the pre-compressive strain remarkably affects the reverse tensile yield stress and the width of the detwinning-dominant stage during inverse tension process. Similar to stress–strain curve of the uniaxial compression, the curve of reverse tensile yield value also has ‘S＇ shape, and its minimum value is only 38 MPa. The relationship between pre-compressive strain and the width of detwinning-dominant stage presents a linear growth, and the greater the precompressive strain is, the smaller the strain hardening rate of the detwinning-slip-dominant stage is. Compared with the reverse tension under pre-compression, the influence of the pre-tension deformation on the deformation mechanism of subsequent compression is relatively simple. With the increase in pre-tension strain, the yield stress of the reverse loading is rising.
基金financially supported by the National Natural Science Foundation of China(Nos.50775211 and51174189)
文摘Twinning and detwinning are the important deformation modes in magnesium alloys during cyclic loading at room temperature. To analyze these two deformation mechanism, cyclic compression–tension experiments were performed on Mg–3Al–1Zn rolled sheet along the rolling direction. In these tests, the microstructure evolutions of a series of grains during deformation were traced by using quasi in situ electron backscatter diffraction(EBSD). Important quantities like the Schmid factors of twinning system, the fraction of twinning during compression, and the fraction of twinning after reverse loading were calculated on the basis of measured quantities. The influence of Schmid factor of twinning variants on detwinning upon reverse loading was analyzed. Detwinning would prefer to proceed during reverse loading if the Schmid factor of twinning in the twinning area before reverse loading is sufficiently large.
基金financially supported by the National Natural Science Foundation of China (Nos. 51690164 and 51904183)the Shanghai Science and Technology Committee Grant (Nos. 19XD1401600 and 19010500300)the Project funded by China Postdoctoral Science Foundation (Nos. 2018M640375, 2019T120330)。
文摘Specimens with single-phase martensite, net-like γ/martensite mixed structure and lamella-likeγ/martensite mixed structure were designed to investigate the effect of the γ phase on the mechanical behavior and the detwinning of non-modulated(NM) martensitic variant in Ni-rich Ni-Mn-Ga alloys under uniaxial compression. It can be found the existence of the γ phase significantly enhances the compressive stresses, and the net-like γ phase specimen presents a higher value of compressive strain than that of the lamella-like γ phase specimen. Especially, the detwinning plateau of the lamella-like γ phase specimen is almost invisible due to the martensite colonies with low Schmid factors. Finally, according to the calculation of deformation gradient tensor, we found that the tensors along compression direction(εzz) of net-like γ phase/martensite mixed structure specimen and single-phase martensite specimen are lower than that of the specimen with lamella-like γ phase/martensite mixed structure, which well explained the detwinning strain for these specimens. The present study not only highlights the role ofγ phase on the mechanical behavior, but also provides more guidelines for the mechanical training of Ni-Mn-Ga shape memory alloys.
基金supported by the National Natural Science Foundation of China Project(No.51971187)Guangdong Basic and Applied Basic Research Foundation(No.2022A1515011322)+2 种基金PolyU Fund(No.G-YBZ3)funding support to the State Key Laboratories in Hong Kong from the Innovation and Technology Commission of the Government of the HKASR,ChinaSY and LQ were supported by grants from the Research Committee of PolyU under student account codes RK2J and RK2U,respectively.
文摘Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)medium-entropy alloy with an average lamellae thickness of∼20 nm embedded by thinner nanotwins was fabricated by severe cold rolling to achieve superior thermal stability.Compared with the conventional nanotwinned CrCoNi with nanotwins inside ultra-fined grains,the hier-archical nanolaminated-nanotwinned(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8) exhibits a significant annealing-induced hard-ening effect,i.e.,hardness increasing from∼250 HV in the original specimen to∼500 HV in the cold-rolled status and finally∼630 HV after annealing at 600℃for 1 h.Detailed microstructure characterizations reveal that the reduced dislocation density and formation of L1_(2)ordered domain are mainly responsible for such hardening effect,which is facilitated by the effectively suppressed coarsening with annealing temperature,i.e.,slow detwinning process and well-retained low-angle nanolamellar structure.The coarsening mechanisms from the cold-rolled nanolamellae to the fully recrystallized micro-equiaxed structures under the annealing temperatures ranging from 400 to 800℃ were also elucidated by atomic observations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11021262,11172303 and 11132011)National Basic Research Program of China (Grant No. 2012CB937500)
文摘Molecular dynamics simulations are performed to investigate the deformation behavior of nanocrystalline Ni with pre-twin atom structure.The simulation sample is composed of four grains with average size 12 nm.The simulation technique of isobaric-isothermal ensemble(NPT) with high pressure is applied to obtain a sample with two circle twins.Under uniaxial tensile and shear loading,as well as different detwinning deformation behaviors are observed.Under uniaxial tension the detwinning deformation is induced by the event of grain growth,and it is supported by local energy analysis.Under the shear loading the detwinning deformation is related to the loading rate.The results show that there may be a critical shear rate.As the shear rate is sufficiently high the circle twin is found to be failed;as the shear rate is less than that rate,the size of circle twin become smaller and gradually approach a constant value.Our simulation results are in good agreement with experiment observation.
基金supported by Beijing Natural Science Foundation(Z180014)Beijing Outstanding Young Scientists Projects(BJJWZYJH01201910005018)the National Natural Science Foundation of China(51771104)。
文摘Detwinning is an important plastic deformation mechanism that can significantly affect the mechanical properties of twin-structured metals.Although many detwinning mechanisms have been proposed for pure metals,it is unclear whether such a deformation model is valid for nanocrystalline alloys because of the lack of direct evidence.Here,the atomicscale detwinning deformation process of a nanocrystalline AuAg alloy with an average grain size of~15 nm was investigated in situ.The results show that there are three types of detwinning mechanisms in nanocrystalline AuAg alloys.The first type of detwinning results from grain boundary migration.The second type of detwinning occurs through combined layer-by-layer thinning and incoherent twin boundary migration.The last one occurs through incoherent twin boundary migration,which results from the collective motion of partial dislocations in an array.
