How to describe the austenite reverse transformation(ART)has always been considered as a key problem of controlling microstructures and mechanical properties in high-strength steels.So far,numerous studies have been c...How to describe the austenite reverse transformation(ART)has always been considered as a key problem of controlling microstructures and mechanical properties in high-strength steels.So far,numerous studies have been conducted,unfortunately,without fully considering diffusion of elements,interface migration,and interaction between trans-interface diffusion and interface migration,as well as synergy of thermodynamic and kinetic for interfacial migration.A more flexible modeling for the ART is herein developed using thermodynamic extremal principle,where the concept of trans-interface diffusion in two steps,i.e.,from the parent phase to the interface and from the interface to the product phase,as well as the Gibbs energy balance approach,was introduced to predict the behavior of interface migration and element trans-interface diffusion within the migrating interface.Subsequently,the thermodynamic driving force ΔG and the effective kinetic energy barrier Q_(eff) for the ART were also analytically performed,as well as a unified expression for so-called generalized stability(GS).It is demonstrated that the higher driving force in the ART generally results in the increased yield strength,while the larger GS tends to yield improved uniform elongation,thus forming a correspondence between the thermo-kinetics trade-off and the strength-ductility trade-off.Applying a proposed criterion of high ΔG-high GS,the present model can be adopted to design the ART,which will produce the austenite microstructure with high strength and high plasticity,as evidenced by the current experiments.展开更多
The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results sh...The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results show that a higher level of the applied constant stress during the cooling process will induce martensite with a higher reverse martensitic transformation start temperature As and a smaller recovery strain ratio. Similarly, a prestrain at the room temperature elevates the As temperature and decreases the recovery strain ratio. However, the As temperature and the recovery strain ratio of the martensite formed during the cooling process under a constant stress are lower than those of the martensite formed by prestrain at the room temperature.展开更多
The reverse transformation behavior of TiNi alloy wires prestrained at different temperatures is studied in this paper. Experimental results show that prestrain at different temperatures obviously affects the reverse ...The reverse transformation behavior of TiNi alloy wires prestrained at different temperatures is studied in this paper. Experimental results show that prestrain at different temperatures obviously affects the reverse transformation behavior of the TiNi alloy wire. A single peak appears on the DSC curves of wires prestrained at 253-313K (in the martensite state). However deformed at 333K, three consecutive peaks appear on the DSC curves of wires with a smaller prestrain and a single peak appears on the DSC curves of the wires with a larger prestrain. The recovery strain ratio of the wires prestrained at 253-313K are very similar. However, the ratio of the wire predeformed at 333K is obviously smaller than that of the wire prestrained in the martensite state.展开更多
Bidirectional transformations,which are achieved by triggering both dynamic forward transformation from the face-centered-cubic(fcc)austenite to the hexagonal-close-packed(hcp)martensite and the reverse transformation...Bidirectional transformations,which are achieved by triggering both dynamic forward transformation from the face-centered-cubic(fcc)austenite to the hexagonal-close-packed(hcp)martensite and the reverse transformation from martensite to austenite during cold deformation,have been previously reported in FeMnCoCr-based high-entropy alloys(HEAs).This leads to the permanent refinement of microstructure and hence enhances the work-hardening capacity of alloys.In order to reveal the microscopic mechanism of the reverse transformation in HEAs under deformation,the effect of the sample aspect ratio,i.e.,Z/X,on the evolution of deformation systems in the equi-atomic FeMnCoCrNi alloy with[110]orientation during uniaxial tensile loading along the Z direction is investigated by atomic simulations in this study.When the aspect ratio is 0.5,the reverse transformation is more significant compared with other models,while a good plasticity can still be maintained.We then compare the micromechanical behavior of three fcc single crystals,i.e.,FeMnCoCrNi,FeCuCoCrNi,and pure Cu.The results show that the stacking fault energy plays a major role in the activation of different deformation mechanisms;however,the lattice distortion in the HEA does not significantly affect the activation of deformation systems.Furthermore,for all materials dislocation slip leads to the softening,while strain hardening is attributed to the initiation of multiple deformation mechanisms.The Shockley partials slip leads to bidirectional phase transition,twinning and detwinning in the three materials.Thus,the reverse transformation can occur in all metallic materials where the fcc to hcp phase transformation is the dominant deformation mechanism.These findings contribute to an in-depth understanding of the deformation mechanism in fcc-structured materials under severe plastic deformation and provide theoretical guidance for the design of alloys with superior strength–plasticity combinations.展开更多
Based on the nonlocal nonlinear Schr6dinger equation, the propagation properties of anomalous hollow beams in strongly isotropic nonlocal media are investigated. The analytical expressions of the beam propagation, the...Based on the nonlocal nonlinear Schr6dinger equation, the propagation properties of anomalous hollow beams in strongly isotropic nonlocal media are investigated. The analytical expressions of the beam propagation, the on-axis intensity and the beam width are obt.ained. The results show that the evolution of the beam is periodical and the input power is the most important parameter. The input power determines the variation of the period. Furthermore, it is found that there exists a critical input power in the x direction and in the y direction separately when the initial beam widths in the two transversal directions are unequal. The beam width remains invariant in the corresponding transversal direction when the input power equals the critical power in one of the transversal directions. Selecting a properinput power, the beam can be broadened or compressed in the two transversal directions at the same time, In particular, the beam can be broadened （compressed） in one transversal direction, whereas in the other transversal direction, it is compressed （broadened）, i.e., the transversal reverse transformation.展开更多
The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is...The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is significantly different from that of the TiNi alloys prestrained in the martensite phase. Three continual peaks appear on the DSC curves of wires with a small prestrain and one high temperature peak appears on the DSC curves of wires with a large prestrain.展开更多
The actuation mechanism of TiNi shape memory alloy wires, which were deformed at parent phase followed by a cooling process under constant strain constraint, was investigated. The experimental results show that the tw...The actuation mechanism of TiNi shape memory alloy wires, which were deformed at parent phase followed by a cooling process under constant strain constraint, was investigated. The experimental results show that the two-step reverse martensitic transformation behavior occurs during the heating process, and the temperature range of reverse transformation was obviously widened with the increasing of prestrain. The recovery strain vs temperature curves exhibits an actuation characteristic of linear output recovery strain in a wide temperature range.展开更多
Microstructure of metastable austenitic manganese steel after reverse transformation treatment was investi gated using optical microscopy, X ray diffraction （XRD）, electrical resistivity and hardness testing. Austen...Microstructure of metastable austenitic manganese steel after reverse transformation treatment was investi gated using optical microscopy, X ray diffraction （XRD）, electrical resistivity and hardness testing. Austenite grain refinement was successfully achieved by a two-step heat treatment. First, martensite was produced by cooling the so- lution-treated samples to --196 ℃. Then, the deep cryogenic treated samples were heated to 850 ℃ upon slow or rapid heating. The mean size of original austenite grain was about 400 fire. But the mean size of equiaxed reversion austenite was refined to 50 μm. Microstructure evolution and electrical resistivity change showed that martensite plates underwent tempering action upon slow heating, and the residual austenite was decomposed, resulting in the formation of pearlite nodules at the austenite grains boundaries. The refinement mechanism upon slow heating is the diffusion-controlled nucleation and growth of austenite. However, the reverse transformation upon rapid heating was predominated by displacive manner. The residual austenite was not decomposed. The plate α-phase was carbon-super- saturated until the starting of reverse transformation. The reverse transformation was accompanied by surface effect, resulting in the formation of plate austenite with high density dislocations. The refinement mechanism upon rapid heating is the recrystallization of displacive reversed austenite.展开更多
To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and me...To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870A degrees C for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850A degrees C, where grains with a diameter ae<currency> 500 nm accounted for 30% and those with a diameter > 0.5 mu m accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.展开更多
DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation in...DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation increased with increasing degree of predeformation, but the algebraic difference between As and Af decreased with increasing predeformation until it reached a minimum value, then remained unchanged with further deformation. Transformation heat also increased with increasing predeformation until it reached a maximum value, then decreased with further predeformation. All the phenomena above were considered to be closely related with the release of elastic strain energy during predeformation.展开更多
Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and inte...Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and intelligent/smart devices.In this work,the magnetic-field-induced metamagnetic reverse martensitic transformation(MFIRMT)from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering.The martensitic transformation temperature Tmreduces quasi-linearly with increasing Fe-content.In strikingly contrast with the Fe-free alloys,the magnetization difference(M')across martensitic transformation increases by three orders of magnitude for Fe-doped alloys.The increased M'should be ascribed to the reduction of Tm,almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content.The large M'provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects,such as magnetocaloric,magnetoresistance and magnetostriction effects.Meanwhile,giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved.Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.展开更多
Mechanism of FCC→HCP reverse phase transformation in face-centered cubic zirconium(FCC-Zr)along with a concomitant 70.5°rotation ofα-Zr matrix were investigated in zircaloy-4(Zr-4)cladding tube by using transmi...Mechanism of FCC→HCP reverse phase transformation in face-centered cubic zirconium(FCC-Zr)along with a concomitant 70.5°rotation ofα-Zr matrix were investigated in zircaloy-4(Zr-4)cladding tube by using transmission electron microscopy(TEM).Results showed that the interaction among a secondary phase particle(SPP)and three FCC-Zr grains resulted in the formation of cross stacking faults in SPP and exerted a drag force on minor axis of the adjacent FCC-Zr phase.Moreover,when the shear stress along[112]_(FCC-Zr)direction was large enough to initiate the emission of 1/6[112]Shockley partial dislocation on every other(111)_(FCC-Zr)close-packed plane,the stacking sequence would change from ABC ABCA to AB ABABA viz.(0001)planes of the daughter HCP phase.Thus,FCC→HCP reverse phase transformation in FCC-Zr was presented.展开更多
To simultaneously enhance the strength−plasticity synergy and resistance to hydrogen embrittlement(HE),the post-annealing treatment was conducted in a laser powder-bed fusion Ti−6Al−4V alloy to introduce reversible tr...To simultaneously enhance the strength−plasticity synergy and resistance to hydrogen embrittlement(HE),the post-annealing treatment was conducted in a laser powder-bed fusion Ti−6Al−4V alloy to introduce reversible transformation.The microstructure,mechanical properties,and HE behavior of the alloy were analyzed by electron back-scattered diffraction,transmission electron microscopy,slow-strain-rate tensile test,hydrogen permeation and thermal desorption spectroscopy.The as-printed sample exhibited high strength but limited elongation and high HE sensitivity.When annealed at 550℃,the elongation was improved but the hydrogen diffusion rate also increased,thus promoting the formation of brittle hydride.When annealed at 750℃,the reversible transformationα'→β→α'occurred and anα'/β/α'sandwich structure formed,thereby enhancing HE resistance(reducing the total elongation loss to 12%)while maintaining high strength(~1116 MPa).The introduction of nanoscaleβ-phase and soft-orientedα'grain significantly inhibited hydride formation and hydrogen-induced crack propagation.展开更多
High entropy alloys(HEAs)have attracted much attention for their excellent mechanical properties stem-ming from diverse deformation mechanisms.Particularly,face-centered cubic(FCC)to body-centered cu-bic(BCC)martensit...High entropy alloys(HEAs)have attracted much attention for their excellent mechanical properties stem-ming from diverse deformation mechanisms.Particularly,face-centered cubic(FCC)to body-centered cu-bic(BCC)martensitic transformation is crucial for enhancing the strength and plasticity of HEAs,partic-ularly at cryogenic temperatures.However,the fundamental atomic mechanism underlying martensitic transformation remains elusive,and the impact of martensitic transformation on the mechanical prop-erties of HEAs at room temperature is unknown.Here,we report in situ atomic-scale observation of a reversible martensitic transformation from FCC to body-centered tetragonal(BCT)and ultimately back to FCC in the nanostructured CrMnFeCoNi HEA at room temperature under deformation.This martensitic transformation is completed by the synergistic action of 90°partial dislocations slip on(111)FCC plane and atom shuffling,involving the periodic arrangement and slip of two 90°half Shockley partial disloca-tions a/12[112](111)and one 90°Shockley partial dislocation-a/6[112](111)on three successive(111)FCC atomic planes.Additionally,the reversible phase transformation induced by high stress dissipates strain energies and hinders crack propagation,thereby enhancing the fracture toughness of HEAs.Our findings contribute to a deeper comprehension of the martensitic transformation mechanisms in HEAs,offering valuable insights for improving their mechanical properties.展开更多
A 0.06%C low carbon steel was deformed in torsion over the temperature range 877-917℃in a 2% H_2 - Ar gas atmosphere.Strains of 0.25 -5.0 were applied at strain rates ofε= 0.04 s^(-1) andε= 0.4 s^(-1) to study the ...A 0.06%C low carbon steel was deformed in torsion over the temperature range 877-917℃in a 2% H_2 - Ar gas atmosphere.Strains of 0.25 -5.0 were applied at strain rates ofε= 0.04 s^(-1) andε= 0.4 s^(-1) to study the formation of ferrite by dynamic transformation(DT) at temperatures above the A_(e3).The critical strain for ferrite formation by DT was aboutε= 0.2 and its volume fraction increased with strain and decreased with temperature above the A_(e3).Average ferrite grain sizes of 1.5μm to 5μm were produced,which decreased with strain rate.At the lower strain rate(ε= 0.04 s^(-1)) reverse transformation(RT) took place during deformation once an incubation time of about 40 s,was exceeded.An increase in strain rate fromε= 0.04 s^(-1) toε= 0.4 s^(-1) arrested RT during testing at all temperatures as the total test times did not exceed 13 s.The present work shows that DT is favored at higher strain rates by increasing the driving force(i.e.stored energy ) and by suppressing RT.展开更多
Recently,a reversible image transformation(RIT)technology that transforms a secret image to a freely-selected target image is proposed.It not only can generate a stego-image that looks similar to the target image,but ...Recently,a reversible image transformation(RIT)technology that transforms a secret image to a freely-selected target image is proposed.It not only can generate a stego-image that looks similar to the target image,but also can recover the secret image without any loss.It also has been proved to be very useful in image content protection and reversible data hiding in encrypted images.However,the standard deviation(SD)is selected as the only feature during the matching of the secret and target image blocks in RIT methods,the matching result is not so good and needs to be further improved since the distributions of SDs of the two images may be not very similar.Therefore,this paper proposes a Gray level co-occurrence matrix(GLCM)based approach for reversible image transformation,in which,an effective feature extraction algorithm is utilized to increase the accuracy of blocks matching for improving the visual quality of transformed image,while the auxiliary information,which is utilized to record the transformation parameters,is not increased.Thus,the visual quality of the stego-image should be improved.Experimental results also show that the root mean square of stego-image can be reduced by 4.24%compared with the previous method.展开更多
The influence of heating rate on double reversible transformation in CuZnAlMnNi shape memory alloy was investigated by differential scanning calorimetry. It was found that rapid heating inhibits X -->M transformati...The influence of heating rate on double reversible transformation in CuZnAlMnNi shape memory alloy was investigated by differential scanning calorimetry. It was found that rapid heating inhibits X -->M transformation but is favorable to the reverse martensite transformation, giving rise to the approach of the two transformation peaks. With the decrease of heating rate, the two transformation peaks separate gradually.展开更多
Internal friction(IF)spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy(SMA)samples were measured wi...Internal friction(IF)spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy(SMA)samples were measured with a dynamic mechanical analyzer,respectively.The IF spectra were characterized by IF peak increasing progressively and peak shifting toward high temperature with an increase in temperature rate.An iterative approach was used to calculate the precise intrinsic and approximate transitory IF contributions to the normal IF spectrum.The quantitatively analyzed results indicate that the transitory IF of this alloy is nonlinearly dependent on the temperature rate and obeys a power law with a power coefficient of 0.55.The predicted and experimental IF spectra at different temperature rates of 0.75 and 1°C/min agree well with each other,respectively.展开更多
The apparent activation energies and frequency factors of thedouble reversible transformations occurring in heating CuZnAlMnNIshape memory alloy (SMA) were deduced as ΔE_x→M = 62. 597 8 KJ/mol, ΔE_M → A = 153. 92 ...The apparent activation energies and frequency factors of thedouble reversible transformations occurring in heating CuZnAlMnNIshape memory alloy (SMA) were deduced as ΔE_x→M = 62. 597 8 KJ/mol, ΔE_M → A = 153. 92 KJ/Mol, A_x→M = 5.2232 × 10~9S^-1, andA_ M → A = 2.3251 × 10~23 S^-1, respectively. The kinetic equationsof the two transformations due- Ing heating were establishedsimultaneously.展开更多
304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electro...304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52130110,52271116,52431002)the Fundamental Research Funds for the Central Universities(No.D5000220052)the Aeronautical Science Foundation of China(2023Z053053003).
文摘How to describe the austenite reverse transformation(ART)has always been considered as a key problem of controlling microstructures and mechanical properties in high-strength steels.So far,numerous studies have been conducted,unfortunately,without fully considering diffusion of elements,interface migration,and interaction between trans-interface diffusion and interface migration,as well as synergy of thermodynamic and kinetic for interfacial migration.A more flexible modeling for the ART is herein developed using thermodynamic extremal principle,where the concept of trans-interface diffusion in two steps,i.e.,from the parent phase to the interface and from the interface to the product phase,as well as the Gibbs energy balance approach,was introduced to predict the behavior of interface migration and element trans-interface diffusion within the migrating interface.Subsequently,the thermodynamic driving force ΔG and the effective kinetic energy barrier Q_(eff) for the ART were also analytically performed,as well as a unified expression for so-called generalized stability(GS).It is demonstrated that the higher driving force in the ART generally results in the increased yield strength,while the larger GS tends to yield improved uniform elongation,thus forming a correspondence between the thermo-kinetics trade-off and the strength-ductility trade-off.Applying a proposed criterion of high ΔG-high GS,the present model can be adopted to design the ART,which will produce the austenite microstructure with high strength and high plasticity,as evidenced by the current experiments.
基金supported by the National Natural Science Foundation of the People’s Republic of China under grant No.50071037.
文摘The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results show that a higher level of the applied constant stress during the cooling process will induce martensite with a higher reverse martensitic transformation start temperature As and a smaller recovery strain ratio. Similarly, a prestrain at the room temperature elevates the As temperature and decreases the recovery strain ratio. However, the As temperature and the recovery strain ratio of the martensite formed during the cooling process under a constant stress are lower than those of the martensite formed by prestrain at the room temperature.
基金This work is funded by the National Natural Science Foundation the Peoples Republic of China (No. 50071037)
文摘The reverse transformation behavior of TiNi alloy wires prestrained at different temperatures is studied in this paper. Experimental results show that prestrain at different temperatures obviously affects the reverse transformation behavior of the TiNi alloy wire. A single peak appears on the DSC curves of wires prestrained at 253-313K (in the martensite state). However deformed at 333K, three consecutive peaks appear on the DSC curves of wires with a smaller prestrain and a single peak appears on the DSC curves of the wires with a larger prestrain. The recovery strain ratio of the wires prestrained at 253-313K are very similar. However, the ratio of the wire predeformed at 333K is obviously smaller than that of the wire prestrained in the martensite state.
基金financially supported by the National Key R&D Program of China(No.2021YFA1200202)the National Natural Science Foundation of China(No.51922026)+2 种基金the Fundamental Research Funds for the Central Universities(Nos.N2002005,N2007011)the Liaoning Natural Science Foundation(No.20180510010)the 111 Project(No.B20029)。
文摘Bidirectional transformations,which are achieved by triggering both dynamic forward transformation from the face-centered-cubic(fcc)austenite to the hexagonal-close-packed(hcp)martensite and the reverse transformation from martensite to austenite during cold deformation,have been previously reported in FeMnCoCr-based high-entropy alloys(HEAs).This leads to the permanent refinement of microstructure and hence enhances the work-hardening capacity of alloys.In order to reveal the microscopic mechanism of the reverse transformation in HEAs under deformation,the effect of the sample aspect ratio,i.e.,Z/X,on the evolution of deformation systems in the equi-atomic FeMnCoCrNi alloy with[110]orientation during uniaxial tensile loading along the Z direction is investigated by atomic simulations in this study.When the aspect ratio is 0.5,the reverse transformation is more significant compared with other models,while a good plasticity can still be maintained.We then compare the micromechanical behavior of three fcc single crystals,i.e.,FeMnCoCrNi,FeCuCoCrNi,and pure Cu.The results show that the stacking fault energy plays a major role in the activation of different deformation mechanisms;however,the lattice distortion in the HEA does not significantly affect the activation of deformation systems.Furthermore,for all materials dislocation slip leads to the softening,while strain hardening is attributed to the initiation of multiple deformation mechanisms.The Shockley partials slip leads to bidirectional phase transition,twinning and detwinning in the three materials.Thus,the reverse transformation can occur in all metallic materials where the fcc to hcp phase transformation is the dominant deformation mechanism.These findings contribute to an in-depth understanding of the deformation mechanism in fcc-structured materials under severe plastic deformation and provide theoretical guidance for the design of alloys with superior strength–plasticity combinations.
基金supported by the National Natural Science Foundation of China(Grant Nos.61308016,11374089,and 11347121)the Natural Science Foundationof Hebei Province,China(Grant Nos.A2012205023,F2012205076,and A2012205085)+3 种基金the Natural Science Foundation of Hunan Province,China(GrantNo.13JJ4097)the China Postdoctoral Science Foundation(Grant No.2014M551041)the Research Foundation of Education Bureau of Hebei Province,China(Grant No.ZD20131014)Hebei Normal University Foundation,China(Grant No.L2011B06)
文摘Based on the nonlocal nonlinear Schr6dinger equation, the propagation properties of anomalous hollow beams in strongly isotropic nonlocal media are investigated. The analytical expressions of the beam propagation, the on-axis intensity and the beam width are obt.ained. The results show that the evolution of the beam is periodical and the input power is the most important parameter. The input power determines the variation of the period. Furthermore, it is found that there exists a critical input power in the x direction and in the y direction separately when the initial beam widths in the two transversal directions are unequal. The beam width remains invariant in the corresponding transversal direction when the input power equals the critical power in one of the transversal directions. Selecting a properinput power, the beam can be broadened or compressed in the two transversal directions at the same time, In particular, the beam can be broadened （compressed） in one transversal direction, whereas in the other transversal direction, it is compressed （broadened）, i.e., the transversal reverse transformation.
基金Funded by the National Natural Science Foundation of China(No.50071037)
文摘The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is significantly different from that of the TiNi alloys prestrained in the martensite phase. Three continual peaks appear on the DSC curves of wires with a small prestrain and one high temperature peak appears on the DSC curves of wires with a large prestrain.
基金FundedbytheNationalNaturalScienceFoundationofChi na (No .5 0 0 710 37)
文摘The actuation mechanism of TiNi shape memory alloy wires, which were deformed at parent phase followed by a cooling process under constant strain constraint, was investigated. The experimental results show that the two-step reverse martensitic transformation behavior occurs during the heating process, and the temperature range of reverse transformation was obviously widened with the increasing of prestrain. The recovery strain vs temperature curves exhibits an actuation characteristic of linear output recovery strain in a wide temperature range.
基金Sponsored by National Natural Science Foundation of China(51071075)
文摘Microstructure of metastable austenitic manganese steel after reverse transformation treatment was investi gated using optical microscopy, X ray diffraction （XRD）, electrical resistivity and hardness testing. Austenite grain refinement was successfully achieved by a two-step heat treatment. First, martensite was produced by cooling the so- lution-treated samples to --196 ℃. Then, the deep cryogenic treated samples were heated to 850 ℃ upon slow or rapid heating. The mean size of original austenite grain was about 400 fire. But the mean size of equiaxed reversion austenite was refined to 50 μm. Microstructure evolution and electrical resistivity change showed that martensite plates underwent tempering action upon slow heating, and the residual austenite was decomposed, resulting in the formation of pearlite nodules at the austenite grains boundaries. The refinement mechanism upon slow heating is the diffusion-controlled nucleation and growth of austenite. However, the reverse transformation upon rapid heating was predominated by displacive manner. The residual austenite was not decomposed. The plate α-phase was carbon-super- saturated until the starting of reverse transformation. The reverse transformation was accompanied by surface effect, resulting in the formation of plate austenite with high density dislocations. The refinement mechanism upon rapid heating is the recrystallization of displacive reversed austenite.
基金supported by the National Natural Science Foundation of China(Grant No.51474031)
文摘To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870A degrees C for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850A degrees C, where grains with a diameter ae<currency> 500 nm accounted for 30% and those with a diameter > 0.5 mu m accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.
基金the National Natural Science Foundation of China under grant No. 59601004,59731030.
文摘DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation increased with increasing degree of predeformation, but the algebraic difference between As and Af decreased with increasing predeformation until it reached a minimum value, then remained unchanged with further deformation. Transformation heat also increased with increasing predeformation until it reached a maximum value, then decreased with further predeformation. All the phenomena above were considered to be closely related with the release of elastic strain energy during predeformation.
基金financially supported by the Key Project of Natural Science Foundation of Jiangxi Province(No.20192ACB20004)the National Natural Science Foundation of China(No.51671097)the Open Project awarded by National Key Laboratory State Microstructures Physics(No.M32037)。
文摘Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and intelligent/smart devices.In this work,the magnetic-field-induced metamagnetic reverse martensitic transformation(MFIRMT)from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering.The martensitic transformation temperature Tmreduces quasi-linearly with increasing Fe-content.In strikingly contrast with the Fe-free alloys,the magnetization difference(M')across martensitic transformation increases by three orders of magnitude for Fe-doped alloys.The increased M'should be ascribed to the reduction of Tm,almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content.The large M'provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects,such as magnetocaloric,magnetoresistance and magnetostriction effects.Meanwhile,giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved.Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.
基金The authors appreciate Dr.Jinmin Liu and Dr.Xiaolan Wang for TEM measurements.
文摘Mechanism of FCC→HCP reverse phase transformation in face-centered cubic zirconium(FCC-Zr)along with a concomitant 70.5°rotation ofα-Zr matrix were investigated in zircaloy-4(Zr-4)cladding tube by using transmission electron microscopy(TEM).Results showed that the interaction among a secondary phase particle(SPP)and three FCC-Zr grains resulted in the formation of cross stacking faults in SPP and exerted a drag force on minor axis of the adjacent FCC-Zr phase.Moreover,when the shear stress along[112]_(FCC-Zr)direction was large enough to initiate the emission of 1/6[112]Shockley partial dislocation on every other(111)_(FCC-Zr)close-packed plane,the stacking sequence would change from ABC ABCA to AB ABABA viz.(0001)planes of the daughter HCP phase.Thus,FCC→HCP reverse phase transformation in FCC-Zr was presented.
基金the National Natural Science Foundation of China(No.52001213)the“Chen Guang”Project(No.20CG65)supported by the Shanghai Municipal Education Commission,China.
文摘To simultaneously enhance the strength−plasticity synergy and resistance to hydrogen embrittlement(HE),the post-annealing treatment was conducted in a laser powder-bed fusion Ti−6Al−4V alloy to introduce reversible transformation.The microstructure,mechanical properties,and HE behavior of the alloy were analyzed by electron back-scattered diffraction,transmission electron microscopy,slow-strain-rate tensile test,hydrogen permeation and thermal desorption spectroscopy.The as-printed sample exhibited high strength but limited elongation and high HE sensitivity.When annealed at 550℃,the elongation was improved but the hydrogen diffusion rate also increased,thus promoting the formation of brittle hydride.When annealed at 750℃,the reversible transformationα'→β→α'occurred and anα'/β/α'sandwich structure formed,thereby enhancing HE resistance(reducing the total elongation loss to 12%)while maintaining high strength(~1116 MPa).The introduction of nanoscaleβ-phase and soft-orientedα'grain significantly inhibited hydride formation and hydrogen-induced crack propagation.
基金the Natural Science Foundation of China(Nos.52173224,52130105)the Natural Science Foundation of Shanghai(No.21ZR1431200)+2 种基金Shanghai Jiao Tong University-JA Solar New Energy Materials Joint Research Center.Shufen Chu is supported by the China Postdoctoral Science Foundation(No.2023M742218)Fan Zhang is supported by the National Key Lab-oratory Foundation of Science and Technology on Materials under Shock and Impact(No.WDZC2022-1)the National Natural Science Foundation of China((No.52271141).
文摘High entropy alloys(HEAs)have attracted much attention for their excellent mechanical properties stem-ming from diverse deformation mechanisms.Particularly,face-centered cubic(FCC)to body-centered cu-bic(BCC)martensitic transformation is crucial for enhancing the strength and plasticity of HEAs,partic-ularly at cryogenic temperatures.However,the fundamental atomic mechanism underlying martensitic transformation remains elusive,and the impact of martensitic transformation on the mechanical prop-erties of HEAs at room temperature is unknown.Here,we report in situ atomic-scale observation of a reversible martensitic transformation from FCC to body-centered tetragonal(BCT)and ultimately back to FCC in the nanostructured CrMnFeCoNi HEA at room temperature under deformation.This martensitic transformation is completed by the synergistic action of 90°partial dislocations slip on(111)FCC plane and atom shuffling,involving the periodic arrangement and slip of two 90°half Shockley partial disloca-tions a/12[112](111)and one 90°Shockley partial dislocation-a/6[112](111)on three successive(111)FCC atomic planes.Additionally,the reversible phase transformation induced by high stress dissipates strain energies and hinders crack propagation,thereby enhancing the fracture toughness of HEAs.Our findings contribute to a deeper comprehension of the martensitic transformation mechanisms in HEAs,offering valuable insights for improving their mechanical properties.
文摘A 0.06%C low carbon steel was deformed in torsion over the temperature range 877-917℃in a 2% H_2 - Ar gas atmosphere.Strains of 0.25 -5.0 were applied at strain rates ofε= 0.04 s^(-1) andε= 0.4 s^(-1) to study the formation of ferrite by dynamic transformation(DT) at temperatures above the A_(e3).The critical strain for ferrite formation by DT was aboutε= 0.2 and its volume fraction increased with strain and decreased with temperature above the A_(e3).Average ferrite grain sizes of 1.5μm to 5μm were produced,which decreased with strain rate.At the lower strain rate(ε= 0.04 s^(-1)) reverse transformation(RT) took place during deformation once an incubation time of about 40 s,was exceeded.An increase in strain rate fromε= 0.04 s^(-1) toε= 0.4 s^(-1) arrested RT during testing at all temperatures as the total test times did not exceed 13 s.The present work shows that DT is favored at higher strain rates by increasing the driving force(i.e.stored energy ) and by suppressing RT.
基金This work is supported by the National Key R&D Program of China under grant 2018YFB1003205by the National Natural Science Foundation of China under grant 61502242,U1536206,U1405254,61772283,61602253,61672294+2 种基金by the Jiangsu Basic Research Programs-Natural Science Foundation under grant numbers BK20150925 and BK20151530by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)fundby the Collaborative Innovation Center of Atmospheric Environment and Equipment Technology(CICAEET)fund,China.
文摘Recently,a reversible image transformation(RIT)technology that transforms a secret image to a freely-selected target image is proposed.It not only can generate a stego-image that looks similar to the target image,but also can recover the secret image without any loss.It also has been proved to be very useful in image content protection and reversible data hiding in encrypted images.However,the standard deviation(SD)is selected as the only feature during the matching of the secret and target image blocks in RIT methods,the matching result is not so good and needs to be further improved since the distributions of SDs of the two images may be not very similar.Therefore,this paper proposes a Gray level co-occurrence matrix(GLCM)based approach for reversible image transformation,in which,an effective feature extraction algorithm is utilized to increase the accuracy of blocks matching for improving the visual quality of transformed image,while the auxiliary information,which is utilized to record the transformation parameters,is not increased.Thus,the visual quality of the stego-image should be improved.Experimental results also show that the root mean square of stego-image can be reduced by 4.24%compared with the previous method.
文摘The influence of heating rate on double reversible transformation in CuZnAlMnNi shape memory alloy was investigated by differential scanning calorimetry. It was found that rapid heating inhibits X -->M transformation but is favorable to the reverse martensite transformation, giving rise to the approach of the two transformation peaks. With the decrease of heating rate, the two transformation peaks separate gradually.
文摘Internal friction(IF)spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy(SMA)samples were measured with a dynamic mechanical analyzer,respectively.The IF spectra were characterized by IF peak increasing progressively and peak shifting toward high temperature with an increase in temperature rate.An iterative approach was used to calculate the precise intrinsic and approximate transitory IF contributions to the normal IF spectrum.The quantitatively analyzed results indicate that the transitory IF of this alloy is nonlinearly dependent on the temperature rate and obeys a power law with a power coefficient of 0.55.The predicted and experimental IF spectra at different temperature rates of 0.75 and 1°C/min agree well with each other,respectively.
基金the Natural Science Foundation of Shandong Province, Y2001F06.]
文摘The apparent activation energies and frequency factors of thedouble reversible transformations occurring in heating CuZnAlMnNIshape memory alloy (SMA) were deduced as ΔE_x→M = 62. 597 8 KJ/mol, ΔE_M → A = 153. 92 KJ/Mol, A_x→M = 5.2232 × 10~9S^-1, andA_ M → A = 2.3251 × 10~23 S^-1, respectively. The kinetic equationsof the two transformations due- Ing heating were establishedsimultaneously.
基金supported by the National Natural Science Foundation of China(Grant No.51474031)
文摘304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.
