1.Introduction.Twinning is a fundamental mechanism for plastic deformation in many face-centered cubic(FCC)metals having low stacking fault energies(SFEs)[1,2].In particular,twinning-induced plasticity(TWIP)alloys hav...1.Introduction.Twinning is a fundamental mechanism for plastic deformation in many face-centered cubic(FCC)metals having low stacking fault energies(SFEs)[1,2].In particular,twinning-induced plasticity(TWIP)alloys have excellent tensile properties as a result of the intensive twinning activity[3-5].The twin boundaries also have been proven to contribute to an improved strengthening-toughening effect,mechanical stability and even fatigue performance,relative to high-angle grain boundaries and low-angle grain boundaries[6-11].Therefore,it is of major interest to clarify the twinning mechanism and thereby improve the mechanical properties of metallic materials.展开更多
The effects of varying strain rates and deformation temperatures on the microstructure evolution of the FGH4113A alloy were investigated through hot compression experiments.During hot deformation,grain evolution is pr...The effects of varying strain rates and deformation temperatures on the microstructure evolution of the FGH4113A alloy were investigated through hot compression experiments.During hot deformation,grain evolution is primarily governed by dynamic recrystallization(DRX)and twinning primarily.Furthermore,the pinning effect of the primaryγ'phase(γ'p phase)plays a crucial role in grain refinement.Lower strain rates or higher temperatures facilitate DRX,twinning,and the dissolution of theγ'p phase.At 1140℃,significant dissolution of theγ'p phase and the subsequent loss of its pinning effect reduce twinning activity.A unique twinning mechanism,termed“pinning twinning”,is identified,occurring exclusively under the influence of the pinning effect.When grain boundary migration fails to accommodate dislocations due to the pinning effect,grains preferentially eliminate dislocations via twinning,thereby reducing local strain energy.The grain size prediction model is improved by considering the pinning effect.展开更多
The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The spec...The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The specimens were deformed under varying degrees of IPS strain(γ12=0.05,0.10,and 0.15)using a customized jig.Electron backscatter diffraction(EBSD)observations revealed profuse tensile twinning(TTW)even at an IPS strain of 0.05,with its intensity continuously increased as the IPS strain increased.The TTWs progressively engulfed parent grains with increasing shear strain,evolving into an unusual deformation twin morphology.Furthermore,VPSC model predictions confirmed basal slip as the dominant deformation mode at low IPS strains,transitioning to prismatic slip dominance at higher IPS strains.The activity of the TTW mode was significantly higher during the initial stages of IPS strain and saturated to lower values at higher strains.VPSC simulation results also indicated preferential shear accumulation on a single twin system,explaining the phenomenon of a single twin variant engulfing a parent grain.Additionally,the influence of individual slip and twin modes on texture evolution was evaluated through orientation tracking of representative grains at various shear strain increments using VPSC simulation.The simulation results quantitatively highlighted the activities of basal slip,prismatic slip,and tensile twinning,establishing a correlation between texture evolution and the underlying deformation mechanisms.展开更多
Magnesium is distinguished by its highly anisotropic inelastic deformation involving a profuse activity of deformation twinning.Instrumented micro/nano-indentation technique has been widely applied to characterize the...Magnesium is distinguished by its highly anisotropic inelastic deformation involving a profuse activity of deformation twinning.Instrumented micro/nano-indentation technique has been widely applied to characterize the mechanical properties of magnesium,typically through the analysis of the indentation load-depth response,surface topography,and less commonly,the post-mortem microstructure within the bulk material.However,experimental limitations prevent the real-time observation of the evolving microstructure.To bridge this gap,we employ a recently-developed finite-strain model that couples the phase-field method and conventional crystal plasticity to simulate the evolution of the indentation-induced twin microstructure and its interaction with plastic slip in a magnesium single-crystal.Particular emphasis is placed on two aspects:orientation-dependent inelastic deformation and indentation size effects.Several outcomes of our 2D computational study are consistent with prior experimental observations.Chief among them is the intricate morphology of twin microstructure obtained at large spatial scales,which,to our knowledge,represents a level of detail that has not been captured in previous modeling studies.To further elucidate on size effects,we extend the model by incorporating gradient-enhanced crystal plasticity,and re-examine the notion of‘smaller is stronger’.The corresponding results underscore the dominant influence of gradient plasticity over the interfacial energy of twin boundaries in governing the size-dependent mechanical response.展开更多
Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms ...Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance.We conduct non-equilibrium molecular dynamics(NEMD)simulation and X-ray diffraction(XRD)simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg(NP-Mg).Two different deformation modes govern the shock consolidation in NP-Mg,i.e.,deformation twinning at up≤1.5 km s^(-1)and structural disordering,at up≥2.0 km s^(-1).They accelerate the collapse of nanopores and void compaction,giving rise to the final consolidation of NP-Mg.Three types of deformation twinning are emitted in NP-Mg,i.e.,the extension twinning for{1121}(1126),and{1102}〈1101>,and the compression{1122}(1123)twinning.They are prompted via coupling atomic shuffles and slips.Deformation twinning prefers to occur within the grains as shock along<1120>or its approaching direction(A-and B-type grains),originated from the high-angle grain boundaries(HAGB)at compression stage.They are inhibited within the ones as shocking along<0001>and the approaching ones(C-and D-type grains).The release and tension loading facilitates the reversible and irreversible detwinning,for the extension and compression twinning,respectively,within the A-and B-type grains.It also contributes to a compression-tension asymmetry for twinning,i.e.,release and tension induced extension twinning within the C-and D-type grains.The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at up≤1.5 km s^(-1),and structural disordering at up≥2.0 km s^(-1).展开更多
Theoretically,a twinning dislocation must stay on the twinning plane which is the first invariant plane of a twinning mode,because the glide of twinning dislocation linearly transforms the parent lattice to the twin l...Theoretically,a twinning dislocation must stay on the twinning plane which is the first invariant plane of a twinning mode,because the glide of twinning dislocation linearly transforms the parent lattice to the twin lattice.However,recent experimental observations showed that a{1011}{1012}twin variant could cross another variant during twin-twin interaction.It is well known that{1011}twinning is mediated by zonal twinning dislocations.Thus,how the zonal twinning dislocations transmute during twin-twin interaction is of great interest but not well understood.In this work,atomistic simulation is performed to investigate interaction between{1011}twin variants.Our results show that when an incoming twin variant impinges on the other which acts as a barrier,surprisingly,the barrier twin can grow at the expense of the incoming twin.Eventually one variant consumes the other.Structural analysis shows that the twinning dislocations of the barrier variant are able to penetrate the zone of twin-twin intersection,by plowing through the lattice of one variant and transform its lattice into the lattice of the other.Careful lattice correspondence analysis reveals that,the lattice transformation from one variant to the other is close to{1012}{1011}twinning,but the orientation relationship deviates by a minor lattice rotation.This deviation presents a significant energy barrier to the lattice transformation,and thus it is expected such a twin-twin interaction will increase the stress for twin growth.展开更多
Grain boundary(GB)deformation and twinning behavior have been recognized as important contributors to the plasticity of polycrystalline materials.However,a comprehensive understanding of dynamic interplay between GB d...Grain boundary(GB)deformation and twinning behavior have been recognized as important contributors to the plasticity of polycrystalline materials.However,a comprehensive understanding of dynamic interplay between GB deformation and twinning behavior remains largely elusive.Using in situ nanomechanical testing,we reveal that GB plasticity and twinning plasticity can be strongly coupled in the context of various deformation characteristics,including lamellae-type twinning from GBs,GB splitting-induced twinning,twinning from triple junctions(TJs),and GB-mediated hierarchical twinning.These GB/TJ-associated twinning modes often arise from the combined effect of macroscopic(geometry-dominated)and microscopic(excess volume-dominated)degrees of freedom of GBs/TJs as an effective way to alleviate local stress concentration,which in turn provides a chance of adjusting GB mobility and enhancing the coordinated evolution of entire interface network in three-dimensional space.Such coupling between GB plasticity and twinning plasticity should represent a general deformation mode in different metallic materials,holding important implications for preventing premature GB cracking and enhancing material ductility.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
Industry pure zirconium sheets with a strong c-axis fiber texture were rolled to different strains at 77 K to investigate the twinning behavior and deformation mechanism. The microstructure and texture of the rolled s...Industry pure zirconium sheets with a strong c-axis fiber texture were rolled to different strains at 77 K to investigate the twinning behavior and deformation mechanism. The microstructure and texture of the rolled specimens were characterized by scanning electron microscopy （SEM） together with electron backscatter diffraction （EBSD） techniques. The results show that the {1022} （1123） compression twinning mode is the dominant deformation twin at low strains loaded along the c-axis, and the {1012} （ 10]- 1 ） tensile twinning generates as the second twin in {1022} （ 1123 ） twins. The selection of twinning modes is governed by Schmid factor （SF） due to the calculating of SF and the EBSD simulating of twinning distribution. The evolution of texture during rolling affected by twins with increase of the strain was explained.展开更多
The morphology and orientation of the growth twins formed in the cast Mg-Zn-Cu-Zr alloys aged at 100 ＆#176;C were characterized using optical microscopy and transmission electron microscopy. It was found that twins w...The morphology and orientation of the growth twins formed in the cast Mg-Zn-Cu-Zr alloys aged at 100 ＆#176;C were characterized using optical microscopy and transmission electron microscopy. It was found that twins were invisible in the as-cast or solutionized Mg-Zn-Cu-Zr alloys while {10 12} twins were exclusively formed in the aged condition. The twinning behavior was significantly affected by two factors, namely, the Zn content and the heat treatment process. A possible formation mechanism of such growth twins was discussed using the viewpoint of vacancy.展开更多
In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechan...In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.展开更多
Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at ...Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at various strain rates.Experimental results indicate symmetric yielding stress under both tension and compression at all strain rates,along with a reduction in the tension-compression asym-metry of ultimate stress and plastic strain as the strain rate increases.This trend arises from an unusual strain rate-dependent tension-compression asymmetry,characterized by strain rate toughening in tension and negligible strain rate effect in compression.The differing behavior is linked to the distinct twinning mechanisms under tension and compression.The suppression of twinning under tension contributes to the positive strain rate dependence of pyramidal slip,whereas the activation of abundant twins during compression means that pyramidal slip is unnecessary to accommodate c-axis strain,leading to the ab-sence of a strain rate effect in compression.Abundant twins nucleate consistently from yielding to 2%strain,but only after basal and prismaticslip have mediated microplasticity,suggesting that these slip systems reduce the nucleation stress for twinning during compression,resulting in a lower activation stress for twinning compared to tension.This study provides new insights into micromechanisms of the tension-compression asymmetry in cast Mg-Gd-Y alloys and offers practical guidance for the application of these materials in critical components that must endure both tension and compression under varying strain rates.展开更多
Heterogeneous structure exhibits superiority in improving mechanical properties,whereas their effects on fatigue damage properties have rarely been studied.In this work,we employed a high-throughput gradient heat trea...Heterogeneous structure exhibits superiority in improving mechanical properties,whereas their effects on fatigue damage properties have rarely been studied.In this work,we employed a high-throughput gradient heat treatment method(757−857℃)to rapidly acquire the solution microstructure of the Ti-6554 alloy with different recrystallization degrees(0%,40%and 100%),followed by the same aging treatment.The results showed that theβ-hetero structure exhibited a yield strength(σ_(YS))of 1403 MPa,an increase of 6.7%,and a remarkable improvement in uniform elongation(UE)of 109.7%,reaching 6.5%,compared to the homogeneous structure.Interestingly,introducing a heterogeneous structure not only overcame the traditional trade-off between strength and ductility but also enhanced fatigue crack propagation(FCP)performance.During FCP process,β-hetero structure,through hetero-deformation induced(HDI)strengthening effects,promoted the accumulation of geometric necessary dislocations(GNDs)within coarseα_(S) phase,enabling faster attainment of the critical shear stress of twinning and increasing twinning density.This facilitated stress relief,improved plastic deformation in the crack tip zone,and increased the critical fast fracture threshold from 30.4 to 36.0 MPa·m^(1/2)showing an enlarged steady state propagation region.This study provides valuable insights on tailoring fatigue damage tolerance through heterogeneous structure for titanium alloys.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
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
Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress(CRSS) compared to the non-basal slip systems(prismatic and pyramidal ) and plays a significant role in texture r...Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress(CRSS) compared to the non-basal slip systems(prismatic and pyramidal ) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.展开更多
The influences of hydrogen on the mechanical properties and the fracture behaviour of Fe-22Mn-0.6C twinning induced plasticity steel have been investigated by slow strain rate tests and fractographic analysis.The stee...The influences of hydrogen on the mechanical properties and the fracture behaviour of Fe-22Mn-0.6C twinning induced plasticity steel have been investigated by slow strain rate tests and fractographic analysis.The steel showed high susceptibility to hydrogen embrittlement,which led to 62.9%and 74.2%reduction in engineering strain with 3.1 and 14.4 ppm diffusive hydrogen,respectively.The fracture surfaces revealed a transition from ductile to brittle dominated fracture modes with the rising hydrogen contents.The underlying deformation and fracture mechanisms were further exploited by examining the hydrogen effects on the dislocation substructure,stacking fault probability,and twinning behaviour in pre-strained slow strain rate test specimens and notched tensile specimens using coupled electron channelling contrast imaging and electron backscatter diffraction techniques.The results reveal that the addition of hydrogen promotes planar dislocation structures,earlier nucleation of stacking faults,and deformation twinning within those grains which have tensile axis orientations close to<111>//rolling direction and<112>//rolling direction.The developed twin lamellae result in strain localization and micro-voids at grain boundaries and eventually lead to grain boundary decohesion.展开更多
The procedure for collecting diffraction data at –173 °C on a twinned specimen of methyl 2-aminopyrazine-3-carboxylate by using the APEX-II software followed by de-twinning the non-merohedrally-twinned reflectio...The procedure for collecting diffraction data at –173 °C on a twinned specimen of methyl 2-aminopyrazine-3-carboxylate by using the APEX-II software followed by de-twinning the non-merohedrally-twinned reflection data with PLATON is described. De-twinning significantly lowers the R index from 0.141 to 0.038 owing to 49% twinning. Crystal data： C6H7N3O2,monoclinic,P21/c （a = 6.3149（1）,b = 16.5274（2）,c = 6.4544（1） A,β = 95.759（1）°,V = 670.24（2） A^3）.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
Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （M...Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52001153,52322105,52271121,52130002 and 52321001)the Youth Innovation Promotion Association CAS(No.202119)+2 种基金the IMR Innovation Fund(No.2023-ZD01)the KC Wong Education Foundation(No.GJTD-2020-09)One of the authors was supported by the European Research Council under grant agreement No.267464-SPDMETALS(TGL).
文摘1.Introduction.Twinning is a fundamental mechanism for plastic deformation in many face-centered cubic(FCC)metals having low stacking fault energies(SFEs)[1,2].In particular,twinning-induced plasticity(TWIP)alloys have excellent tensile properties as a result of the intensive twinning activity[3-5].The twin boundaries also have been proven to contribute to an improved strengthening-toughening effect,mechanical stability and even fatigue performance,relative to high-angle grain boundaries and low-angle grain boundaries[6-11].Therefore,it is of major interest to clarify the twinning mechanism and thereby improve the mechanical properties of metallic materials.
基金supported by the National Key Research and Development Program of China(No.2022YFB3706902)Innovation Project for Graduate Students of Hunan Province+1 种基金China(No.1053320212786)supported in part by the High Performance Computing Center of Central South University,China。
文摘The effects of varying strain rates and deformation temperatures on the microstructure evolution of the FGH4113A alloy were investigated through hot compression experiments.During hot deformation,grain evolution is primarily governed by dynamic recrystallization(DRX)and twinning primarily.Furthermore,the pinning effect of the primaryγ'phase(γ'p phase)plays a crucial role in grain refinement.Lower strain rates or higher temperatures facilitate DRX,twinning,and the dissolution of theγ'p phase.At 1140℃,significant dissolution of theγ'p phase and the subsequent loss of its pinning effect reduce twinning activity.A unique twinning mechanism,termed“pinning twinning”,is identified,occurring exclusively under the influence of the pinning effect.When grain boundary migration fails to accommodate dislocations due to the pinning effect,grains preferentially eliminate dislocations via twinning,thereby reducing local strain energy.The grain size prediction model is improved by considering the pinning effect.
文摘The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The specimens were deformed under varying degrees of IPS strain(γ12=0.05,0.10,and 0.15)using a customized jig.Electron backscatter diffraction(EBSD)observations revealed profuse tensile twinning(TTW)even at an IPS strain of 0.05,with its intensity continuously increased as the IPS strain increased.The TTWs progressively engulfed parent grains with increasing shear strain,evolving into an unusual deformation twin morphology.Furthermore,VPSC model predictions confirmed basal slip as the dominant deformation mode at low IPS strains,transitioning to prismatic slip dominance at higher IPS strains.The activity of the TTW mode was significantly higher during the initial stages of IPS strain and saturated to lower values at higher strains.VPSC simulation results also indicated preferential shear accumulation on a single twin system,explaining the phenomenon of a single twin variant engulfing a parent grain.Additionally,the influence of individual slip and twin modes on texture evolution was evaluated through orientation tracking of representative grains at various shear strain increments using VPSC simulation.The simulation results quantitatively highlighted the activities of basal slip,prismatic slip,and tensile twinning,establishing a correlation between texture evolution and the underlying deformation mechanisms.
文摘Magnesium is distinguished by its highly anisotropic inelastic deformation involving a profuse activity of deformation twinning.Instrumented micro/nano-indentation technique has been widely applied to characterize the mechanical properties of magnesium,typically through the analysis of the indentation load-depth response,surface topography,and less commonly,the post-mortem microstructure within the bulk material.However,experimental limitations prevent the real-time observation of the evolving microstructure.To bridge this gap,we employ a recently-developed finite-strain model that couples the phase-field method and conventional crystal plasticity to simulate the evolution of the indentation-induced twin microstructure and its interaction with plastic slip in a magnesium single-crystal.Particular emphasis is placed on two aspects:orientation-dependent inelastic deformation and indentation size effects.Several outcomes of our 2D computational study are consistent with prior experimental observations.Chief among them is the intricate morphology of twin microstructure obtained at large spatial scales,which,to our knowledge,represents a level of detail that has not been captured in previous modeling studies.To further elucidate on size effects,we extend the model by incorporating gradient-enhanced crystal plasticity,and re-examine the notion of‘smaller is stronger’.The corresponding results underscore the dominant influence of gradient plasticity over the interfacial energy of twin boundaries in governing the size-dependent mechanical response.
基金financially supported by the Natural Science Foundation(NSF)of China(Nos.11802092 and U2230401)NSF of Hunan Province(Nos.2019JJ50221,2019JJ40127,2020JJ5260,and 2020JJ4375)+5 种基金the Funding of the Hunan Education Department Project(Nos.20A248 and 22B0225)the Double first-class construction project of Hunan Agricultural University(No.SYL2019063)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20230682)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20230682)the Postgraduate Scientific Research Innovation Project of Hunan Agricultural University(No.2023XC019)We also acknowledge the support of the computation platform of the National Super Computer Center in Changsha(NSCC).
文摘Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance.We conduct non-equilibrium molecular dynamics(NEMD)simulation and X-ray diffraction(XRD)simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg(NP-Mg).Two different deformation modes govern the shock consolidation in NP-Mg,i.e.,deformation twinning at up≤1.5 km s^(-1)and structural disordering,at up≥2.0 km s^(-1).They accelerate the collapse of nanopores and void compaction,giving rise to the final consolidation of NP-Mg.Three types of deformation twinning are emitted in NP-Mg,i.e.,the extension twinning for{1121}(1126),and{1102}〈1101>,and the compression{1122}(1123)twinning.They are prompted via coupling atomic shuffles and slips.Deformation twinning prefers to occur within the grains as shock along<1120>or its approaching direction(A-and B-type grains),originated from the high-angle grain boundaries(HAGB)at compression stage.They are inhibited within the ones as shocking along<0001>and the approaching ones(C-and D-type grains).The release and tension loading facilitates the reversible and irreversible detwinning,for the extension and compression twinning,respectively,within the A-and B-type grains.It also contributes to a compression-tension asymmetry for twinning,i.e.,release and tension induced extension twinning within the C-and D-type grains.The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at up≤1.5 km s^(-1),and structural disordering at up≥2.0 km s^(-1).
基金support from U.S.National Science Foundation(NSF)(CMMI-2016263,2032483).
文摘Theoretically,a twinning dislocation must stay on the twinning plane which is the first invariant plane of a twinning mode,because the glide of twinning dislocation linearly transforms the parent lattice to the twin lattice.However,recent experimental observations showed that a{1011}{1012}twin variant could cross another variant during twin-twin interaction.It is well known that{1011}twinning is mediated by zonal twinning dislocations.Thus,how the zonal twinning dislocations transmute during twin-twin interaction is of great interest but not well understood.In this work,atomistic simulation is performed to investigate interaction between{1011}twin variants.Our results show that when an incoming twin variant impinges on the other which acts as a barrier,surprisingly,the barrier twin can grow at the expense of the incoming twin.Eventually one variant consumes the other.Structural analysis shows that the twinning dislocations of the barrier variant are able to penetrate the zone of twin-twin intersection,by plowing through the lattice of one variant and transform its lattice into the lattice of the other.Careful lattice correspondence analysis reveals that,the lattice transformation from one variant to the other is close to{1012}{1011}twinning,but the orientation relationship deviates by a minor lattice rotation.This deviation presents a significant energy barrier to the lattice transformation,and thus it is expected such a twin-twin interaction will increase the stress for twin growth.
基金financially supported by the National Key R&D Program of China(No.2021YFA1200201)the National Natural Science Foundation of China(No.52071284)the Zhejiang Provincial Natural Science Foundation of China(No.LR24E010002).
文摘Grain boundary(GB)deformation and twinning behavior have been recognized as important contributors to the plasticity of polycrystalline materials.However,a comprehensive understanding of dynamic interplay between GB deformation and twinning behavior remains largely elusive.Using in situ nanomechanical testing,we reveal that GB plasticity and twinning plasticity can be strongly coupled in the context of various deformation characteristics,including lamellae-type twinning from GBs,GB splitting-induced twinning,twinning from triple junctions(TJs),and GB-mediated hierarchical twinning.These GB/TJ-associated twinning modes often arise from the combined effect of macroscopic(geometry-dominated)and microscopic(excess volume-dominated)degrees of freedom of GBs/TJs as an effective way to alleviate local stress concentration,which in turn provides a chance of adjusting GB mobility and enhancing the coordinated evolution of entire interface network in three-dimensional space.Such coupling between GB plasticity and twinning plasticity should represent a general deformation mode in different metallic materials,holding important implications for preventing premature GB cracking and enhancing material ductility.
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Project(51171213)supported by the National Natural Science Foundation of ChinaProject(NCET-08-0606)supported by New Century Excellent Talents in University,China
文摘Industry pure zirconium sheets with a strong c-axis fiber texture were rolled to different strains at 77 K to investigate the twinning behavior and deformation mechanism. The microstructure and texture of the rolled specimens were characterized by scanning electron microscopy （SEM） together with electron backscatter diffraction （EBSD） techniques. The results show that the {1022} （1123） compression twinning mode is the dominant deformation twin at low strains loaded along the c-axis, and the {1012} （ 10]- 1 ） tensile twinning generates as the second twin in {1022} （ 1123 ） twins. The selection of twinning modes is governed by Schmid factor （SF） due to the calculating of SF and the EBSD simulating of twinning distribution. The evolution of texture during rolling affected by twins with increase of the strain was explained.
基金Project(51201088)supported by the National Natural Science Foundation of ChinaProject(12C0324)supported by the Research Foundation of Education Bureau of Hunan Province,China+1 种基金Project(2011XQD26)supported by Doctoral Scientific Research Foundation of the University of South,ChinaProject([2011]76)supported by the Construct Program of the Key Discipline in Hunan Province,China
文摘The morphology and orientation of the growth twins formed in the cast Mg-Zn-Cu-Zr alloys aged at 100 ＆#176;C were characterized using optical microscopy and transmission electron microscopy. It was found that twins were invisible in the as-cast or solutionized Mg-Zn-Cu-Zr alloys while {10 12} twins were exclusively formed in the aged condition. The twinning behavior was significantly affected by two factors, namely, the Zn content and the heat treatment process. A possible formation mechanism of such growth twins was discussed using the viewpoint of vacancy.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA0410201)the Natural Science Foundation of Heilongjiang Province(No.TD2021E006)+1 种基金the Liaoning Provincial Doctoral Initiation Fund Project(No.2022-BS-008)the China Postdoctoral Science Foundation(No.2023T160654).
文摘In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.
基金the National Natural Science Foundation of China(grant Nos.11988102,52301146,51301173,51531002,52171055,52371037,51601193)the National Key Research and Development Program of China(grant No.2016YFB0301104)+1 种基金the Fundamental Research Funds for the Central Universities(grant No.2023JG007)China Postdoctoral Science Foundation(grant No.8206300226).
文摘Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at various strain rates.Experimental results indicate symmetric yielding stress under both tension and compression at all strain rates,along with a reduction in the tension-compression asym-metry of ultimate stress and plastic strain as the strain rate increases.This trend arises from an unusual strain rate-dependent tension-compression asymmetry,characterized by strain rate toughening in tension and negligible strain rate effect in compression.The differing behavior is linked to the distinct twinning mechanisms under tension and compression.The suppression of twinning under tension contributes to the positive strain rate dependence of pyramidal slip,whereas the activation of abundant twins during compression means that pyramidal slip is unnecessary to accommodate c-axis strain,leading to the ab-sence of a strain rate effect in compression.Abundant twins nucleate consistently from yielding to 2%strain,but only after basal and prismaticslip have mediated microplasticity,suggesting that these slip systems reduce the nucleation stress for twinning during compression,resulting in a lower activation stress for twinning compared to tension.This study provides new insights into micromechanisms of the tension-compression asymmetry in cast Mg-Gd-Y alloys and offers practical guidance for the application of these materials in critical components that must endure both tension and compression under varying strain rates.
基金Project(2021YFB3700801)supported by the National Key Research and Development Program of ChinaProject(2023JJ30683)supported by the Natural Science Foundation of Hunan Province,ChinaProject supported by the State Key Laboratory of Powder Metallurgy(Central South University),China。
文摘Heterogeneous structure exhibits superiority in improving mechanical properties,whereas their effects on fatigue damage properties have rarely been studied.In this work,we employed a high-throughput gradient heat treatment method(757−857℃)to rapidly acquire the solution microstructure of the Ti-6554 alloy with different recrystallization degrees(0%,40%and 100%),followed by the same aging treatment.The results showed that theβ-hetero structure exhibited a yield strength(σ_(YS))of 1403 MPa,an increase of 6.7%,and a remarkable improvement in uniform elongation(UE)of 109.7%,reaching 6.5%,compared to the homogeneous structure.Interestingly,introducing a heterogeneous structure not only overcame the traditional trade-off between strength and ductility but also enhanced fatigue crack propagation(FCP)performance.During FCP process,β-hetero structure,through hetero-deformation induced(HDI)strengthening effects,promoted the accumulation of geometric necessary dislocations(GNDs)within coarseα_(S) phase,enabling faster attainment of the critical shear stress of twinning and increasing twinning density.This facilitated stress relief,improved plastic deformation in the crack tip zone,and increased the critical fast fracture threshold from 30.4 to 36.0 MPa·m^(1/2)showing an enlarged steady state propagation region.This study provides valuable insights on tailoring fatigue damage tolerance through heterogeneous structure for titanium alloys.
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supported by the National Research Foundation of Korea (NRF)grant funded by the Korean government (MSIT) (No.2020R1C1C1004434)。
文摘Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress(CRSS) compared to the non-basal slip systems(prismatic and pyramidal ) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.
文摘The influences of hydrogen on the mechanical properties and the fracture behaviour of Fe-22Mn-0.6C twinning induced plasticity steel have been investigated by slow strain rate tests and fractographic analysis.The steel showed high susceptibility to hydrogen embrittlement,which led to 62.9%and 74.2%reduction in engineering strain with 3.1 and 14.4 ppm diffusive hydrogen,respectively.The fracture surfaces revealed a transition from ductile to brittle dominated fracture modes with the rising hydrogen contents.The underlying deformation and fracture mechanisms were further exploited by examining the hydrogen effects on the dislocation substructure,stacking fault probability,and twinning behaviour in pre-strained slow strain rate test specimens and notched tensile specimens using coupled electron channelling contrast imaging and electron backscatter diffraction techniques.The results reveal that the addition of hydrogen promotes planar dislocation structures,earlier nucleation of stacking faults,and deformation twinning within those grains which have tensile axis orientations close to<111>//rolling direction and<112>//rolling direction.The developed twin lamellae result in strain localization and micro-voids at grain boundaries and eventually lead to grain boundary decohesion.
文摘The procedure for collecting diffraction data at –173 °C on a twinned specimen of methyl 2-aminopyrazine-3-carboxylate by using the APEX-II software followed by de-twinning the non-merohedrally-twinned reflection data with PLATON is described. De-twinning significantly lowers the R index from 0.141 to 0.038 owing to 49% twinning. Crystal data： C6H7N3O2,monoclinic,P21/c （a = 6.3149（1）,b = 16.5274（2）,c = 6.4544（1） A,β = 95.759（1）°,V = 670.24（2） A^3）.
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Project(2012CB932202)supported by the National Basic Research Program of ChinaProjects(50890174,50971088)supported by the National Natural Science Foundation of China
文摘Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.
