A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and...A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and mechanical properties of the fine-grained CS-HEA were characterized.The results showed that as-cast shrinkage cavities and elemental segregation were eliminated.The average grain size was refined from 121.1 to 5.4μm.The face-centered cubic phase fraction increased from 23%to 82%.During tensile deformation,dislocation slip dominated at strains ranging from 5%to 17%,followed by transformation induced plasticity(TRIP)from 17%to 26%,and twin induced plasticity(TWIP)from 26%to 37%.The yield strength,ultimate tensile strength,and elongation of the fine-grained CS-HEA were 503 MPa,1120 MPa,and 37%,respectively.The strength-ductility synergy of fine-grained CS-HEA was attributed to the combined effects of TRIP,TWIP,dislocation strengthening,and fine-grained strengthening.展开更多
Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation...Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.展开更多
In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot al...In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot always provide sufficiently reliable solutions.Nevertheless,Machine Learning(ML)techniques,which offer advanced regression tools to address complicated engineering issues,have been developed and widely explored.This study investigates the selected ML techniques to evaluate their suitability for application in the hot deformation behavior of metallic materials.The ML-based regression methods of Artificial Neural Networks(ANNs),Support Vector Machine(SVM),Decision Tree Regression(DTR),and Gaussian Process Regression(GPR)are applied to mathematically describe hot flow stress curve datasets acquired experimentally for a medium-carbon steel.Although the GPR method has not been used for such a regression task before,the results showed that its performance is the most favorable and practically unrivaled;neither the ANN method nor the other studied ML techniques provide such precise results of the solved regression analysis.展开更多
The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion a...The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.展开更多
Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microst...Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microstructure of the characterization region was analyzed to investigate the recrystallization behavior of 23Cr-8Ni steel.Results show that as the strain rate decreases and the deformation temperature increases,the flow stress decreases.Because the softening phenomenon occurs after the peak stress,the flow stress decreases.The stress index(n)is 4.28,and the thermal deformation activation energy(Q)is 588878 J/mol.Processing map is established,and an optimal thermal processing range of 0.001–0.1 s^(−1) and 1000–1200℃ is achieved,therefore greatly promoting the yield rate.展开更多
The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this s...The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this study,single and dual-phase Ni_(55+x)Mn_(25)Ga_(20-x)(x=0,2,4 and 6)alloys were fabricated.The proportion of theγphase was elevated gradually,and the peak martensitic transformation temperature was enhanced from 350 to 460℃ with an increasing Ni/Ga ratio.The microstructures of theγphase were further regulated from continuous block to dispersed granular after annealing.The annealed dual-phase alloy with x=2 exhibited greater yield stress,compressive strength and toughness than the annealed single-phase alloy.It maintained plastic deformation without fracture,even at a strain of 30%.High strain energy and dislocation density were observed in the martensite of the dual-phase alloy,which can be attributed toγphases and the interface between martensite andγphases.Furthermore,[001]-oriented martensite variants were obtained during deformation in the dual-phase alloy.They were parallel to the loading direction and conducive to improving the compressive strength.This protocol provides in-depth insight into the influence of theγphase on the texture evolution and mechanical behavior of martensite during deformation.展开更多
Bamboo is an important building material with natural hygroscopicity,and the mechanism of water effects on its deformation and fracture behavior has not been fully revealed.For this purpose,a novel in-situ testing met...Bamboo is an important building material with natural hygroscopicity,and the mechanism of water effects on its deformation and fracture behavior has not been fully revealed.For this purpose,a novel in-situ testing method was developed in this study,which coupled Acoustic Emission(AE)and Digital Image Correlation(DIC)techniques.This method was used to investigate the effects of various Moisture Content(MC)levels(0,6%,15%,and 25%)on the tensile behavior of bamboo.The results showed that as the MC increased from 0 to 25%,the tensile strength of bamboo decreased from 163 to 110 MPa,the Young's modulus dropped from 8.5 to 3.9 GPa,and the elongation increased from 4.3 to 14%.An increase in MC could effectively promote the occurrence of subcritical cracks and micro-interfacial dissociations in bamboo.The synergistic effect of these two factors facilitated strain dispersion,ensuring adaptability to large deformations.Additionally,it was found that an increase in MC could significantly alter the fracture mode.This ingenious synergistic effect in bamboo was revealed for the first time in this study.The mechanisms discovered in this study may provide some important insights into the design and fabrication of advanced biomimetic heterostructures and biomimetic interfacial materials.展开更多
Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,whi...Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.展开更多
The effects of solid solution on the deformation behavior of binary Mg-xZn(x=0,1,2 wt%)alloys featuring a designated texture that enables extension twinning under tension parallel to the basal pole in most grains,were...The effects of solid solution on the deformation behavior of binary Mg-xZn(x=0,1,2 wt%)alloys featuring a designated texture that enables extension twinning under tension parallel to the basal pole in most grains,were investigated using in-situ neutron diffraction and the EVPSC-TDT model.Neutron diffraction was used to quantitatively track grain-level lattice strains and diffraction intensity changes(related to mechanical twinning)in differently oriented grains of each alloy during cyclic tensile/compressive loadings.These measurements were accurately captured by the model.The stress-strain curves of Mg-1 wt%Zn and Mg-2 wt%Zn alloys show as-expected solid solution strengthening from the addition of Zn compared to pure Mg.The macroscopic yielding and hardening behaviors are explained by alternating slip and twinning modes as calculated by the model.The solid solution's influence on individual deformation modes,including basal〈a〉slip,prismatic〈a〉slip,and extension twinning,was then quantitatively assessed in terms of activity,yielding behavior,and hardening response by combining neutron diffraction results with crystal plasticity predictions.The Mg-1 wt%Zn alloy displays distinct yielding and hardening behavior due to solid solution softening of prismatic〈a〉slip.Additionally,the dependence of extension twinning,in terms of the twinning volume fraction,on Zn content exhibits opposite trends under tensile and compressive loadings.展开更多
A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate...A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate-high temperatures and high-low stress conditions.The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy,resulting in approximate cubicγ′phases in dendrites and the formation of initial dislocation tangles.After the stress rupture test at 760℃/780 MPa,high content cubicγ′phases,small size of voids as well as preserved dislocation tangles are observed,showing stable structures with high-stress rupture resistance.High content and suitable size of cubicγ′phases,initial dislocation tangles,and L-C locks hinder the dislocation motion,which decreases the minimum strain rate and prolongs life significantly,forming four stress rupture stages.Hence,the defor-mation mechanism is determined by dislocation piled-up onγ/γ′interface,formation of stacking faults inγ′phases,and dislocations shearingγ′phases.However,the microstructure exhibits uneven struc-tures composed of large sizes of raftedγ′phases and voids at 980℃/260 MPa.The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion,resulting in the increase of minimum strain rate,decline of life,and typic three stress rupture stages,even though there are obstacles to dislocation movement caused by dislocation networks.The deformation mecha-nism transforms to form dislocation networks onγ/γ′interface and dislocations shearingγ′phases.Be-sides,the decomposition of carbides on GBs also depends on temperature,which decomposes into harm-ful chain-like M23 C6 carbides at moderate temperatures and reinforced granular-shaped M6 C carbides at high temperatures.The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.展开更多
High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material...High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.展开更多
The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechan...The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechanisms.Currently,there is a lack of comparison and evaluation regarding the suitability of different types of models.In this study,Mg-Gd-Y-Zr alloy is taken as the research object.The hot deformation behavior of the alloy was studied systematically.Subsequently,Arrhenius model with strain compensation,artificial neural network(ANN)model,and ISV model involving dynamic recrystallization(DRX),dislocation density and grain size evolution were established.ANN model demonstrates a higher level of accuracy in fitting the original stress-strain curves compared to both ISV model and modified Arrhenius model,but ANN model is not suitable for predicting the experimental results outside of the initial database.ISV model considers the impact of microstructure evolution history on stress,making it highly effective in reflecting the mechanical responses under complex loading condition.The established ISV model is embedded in the ABAQUS software,which shows good ability in calculating the mechanical response,dimension,and microstructure evolution information of the component during hot forming.展开更多
Ti750s titanium alloy,a novel high-temperature titanium alloy designed for short-term service at elevated temperatures(700–750℃),has previously lacked comprehensive understanding of its hot processing behavior.In th...Ti750s titanium alloy,a novel high-temperature titanium alloy designed for short-term service at elevated temperatures(700–750℃),has previously lacked comprehensive understanding of its hot processing behavior.In this study,the high-temperature deformation behavior and microstructural evolution of the Ti750s alloy were systematically investigated through thermal simulation compression tests conducted at temperatures ranging from 900 to 1070℃and strain rates between 0.1 and 10 s⁻1.A hot processing map was constructed using the dynamic material model to optimize the hot processing parameters.The results indicated that the optimal processing window was between 1040 and 1070℃with a strain rate of 0.1 s⁻1.Processing within the instability region resulted in localized plastic deformation,manifesting as pronounced shear bands and a highly heterogeneous strain distribution;this region should be avoided during hot deformation.Within theα+βphase safety zone characterized by low power dissipation rates between 0.32 and 0.4,the primary deformation mechanism in this region was dynamic recovery(DRV),where the lamellarαgrains underwent deformation and rotation.Conversely,in theα+βphase safety zone with high-power dissipation rates between 0.45 and 0.52,dynamic spheroidization of theαphase and dynamic recrystallization(DRX)of theβphase occurred concurrently.In theβphase safety zone with low power dissipation rates between 0.32 and 0.51,the primary deformation mechanism consisted of DRV ofβgrains,accompanied by limited DRX.However,in theβphase safety zone with high-power dissipation rates exceeding 0.56,both DRV and DRX ofβgrains took place,resulted in a significant increase in the size and number of recrystallized grains compared to those observed under low power dissipation conditions.展开更多
Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and ...Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.展开更多
As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical ...As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.展开更多
The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced n...The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced nonlinearity and multi-scale complexity.This study systematically investigates the hot deformation behavior of Mg-Y-Nd-(Sm)-Zr alloys.Sm alloying promotes recrystallization.The flow stress of Sm-containing alloys declines sharply towards a steady state after reaching its peak value.To overcome the limitations of the Arrhenius-type constitutive(AC)model in predicting complex nonlinear flow behavior,the AC and data hybrid informed neural network(ACINN)model is developed.This approach enhances the predictive accuracy and extends the applicability of the traditional AC model.The evolution of microstructure and recrystallization behavior under hot deformation conditions are investigated based on results from electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The relationship between the power dissipation factor(η)and recrystallization behavior is further examined using K-means clustering analysis.The results demonstrate that dynamic recrystallization(DRX)behavior varies with theηvalue,comprising four distinct regimes:dynamic recovery(DRV),discontinuous dynamic recrystallization(DDRX)dominance,continuous dynamic recrystallization(CDRX)dominance and complete dynamic recrystallization.This analysis presents a new perspective for studying the hot deformation processes of Mg alloys.展开更多
The low cycle fatigue(LCF)behaviors and cyclic deformation mechanisms of 2195 Al-Li alloy were inves-tigated under low temperatures(-20℃and-80℃)and different strain amplitudes(0.6%,0.7%,0.8%,and 1.0%).The LCF stress...The low cycle fatigue(LCF)behaviors and cyclic deformation mechanisms of 2195 Al-Li alloy were inves-tigated under low temperatures(-20℃and-80℃)and different strain amplitudes(0.6%,0.7%,0.8%,and 1.0%).The LCF stress responses under conditions of-20℃&0.6%and-80℃&0.6%exhibited initial cyclic hardening followed by cyclic softening.In contrast,the alloy under other LCF conditions displayed continuous cyclic softening.Notably,the alloy demonstrated reduced LCF life under conditions of-80℃and various strain amplitudes.The fatigue life model based on the total strain energy was developed and proven to be more accurate in predicting fatigue life under diverse LCF conditions.Furthermore,the combined kinematic/isotropic hardening constitutive model exhibited excellent performance in simulat-ing hysteresis loops of the alloy,with corresponding calibration errors all below 14%.Additionally,fatigue fracture surfaces under various LCF conditions consistently exhibited prominent cleavage fracture char-acteristics,and the final fracture zone at-80℃showed increased surface roughness.Finally,the cyclic softening mechanisms were found to be dependent on LCF conditions.The debonding of the interface be-tween the T1 phases and the Al matrix was identified as the primary cyclic softening mechanism under conditions of-20℃&0.6%and-80℃&0.6%.Moreover,the cyclic softening effect under-80℃&1.0%was closely associated with localized shearing of T1 phases.Under-20℃&1.0%,a more pronounced cyclic softening behavior was observed,which was primarily attributed to the continuous shearing of T1 phases.展开更多
Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms...Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(σ_(y))of BCC Fe can be enhanced by increasing the strain rate(ε)and/or decreasing the deformation temperature(T).With the strain rate increasing from ε=10^(2)s^(-1)to 10^(6) s^(-1),the yield strength at 300 K rises from σ_(y)=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength at σ_(y)=10^(3) s^(-1)decreases from σ_(y)=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,ε>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.展开更多
During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis o...During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis of this process is necessary.The isothermal hot compression tests were conducted to investigate the hot deformation behavior of Fe-21Cr-15Ni-5Mn-2Mo steel,a novel austenitic stainless steel,at strain rates from 0.01 to 10 s^(-1)and temperatures ranging from 950 to 1200℃.Based on the true stress-strain curves derived from the tests,the constitutive model and hot working map for the steel were constructed,and the microstructure evolution of the steel was systematically analyzed.The critical deformation conditions for the occurrence of DRX were determined using the plotted work hardening rate curve.The findings indicate a significant rise in flow stress as strain rate increases or deformation temperature decreases.Concurrently,the strain needed to attain peak stress progressively grows.The activation energy for deformation of the steel is 595.511 kJ/mol,which results from the competition between dynamic softening and work hardening during its hot deformation process.Low strain rate and low temperature(0.01 s^(-1),950℃)are the parameters for the instability zone of the steel,and localized flow and deformation bands are the microstructure manifestations of unstable hot processing.The optimal hot working window for the experimental steel is the medium to high strain rate range and medium to high temperature(0.1−10 s^(-1),1100−1200℃),where the microstructure exhibits randomly oriented,uniformly distributed DRX grains.The bulging of the initial grain boundaries is primarily associated with the nucleation mechanism of DRX.Furthermore,based on the critical strain and peak strain,the kinetics of DRX are predicted by the Avrami equation.展开更多
The effects of plastic deformation on precipitation behavior and tensile fracture behavior of Mg-10Gd-3Y-0.6Zr alloy were investigated.The results indicate that more precipitation cores can be provided by the crystal ...The effects of plastic deformation on precipitation behavior and tensile fracture behavior of Mg-10Gd-3Y-0.6Zr alloy were investigated.The results indicate that more precipitation cores can be provided by the crystal defects caused by the plastic deformation,as well as increasing the amount of β＇ phases,and the formation of precipitations at grain boundaries and interfaces between the twins and matrix.Because of an increase in precipitations,the dislocation slipping during deformation process is effectively hindered and the matrix is strengthened,especially for the 2% deformed alloy which can achieve a good combination of strength and ductility.With increasing the plastic deformation,the microcracks occur at the interface between grain boundary precipitations and matrix,and then propagate intergranularly.When intergranular fracture combines with the formation of smoothing facets on the fracture surface,the tensile properties decrease.展开更多
基金the funds of the National Natural Science Fund for Excellent Young Scholars of China(No.52222410)Shaanxi Province National Science Fund for Distinguished Young Scholars,China(No.2022JC-24)the National Natural Science Foundation of China(Nos.52227807,52034005)。
文摘A fine-grained metastable dual-phase Fe_(40)Mn_(20)Co_(20)Cr_(15)Si_(5)high entropy alloy(CS-HEA)with excellent strength and ductility was successfully prepared by friction stir processing(FSP).The microstructural and mechanical properties of the fine-grained CS-HEA were characterized.The results showed that as-cast shrinkage cavities and elemental segregation were eliminated.The average grain size was refined from 121.1 to 5.4μm.The face-centered cubic phase fraction increased from 23%to 82%.During tensile deformation,dislocation slip dominated at strains ranging from 5%to 17%,followed by transformation induced plasticity(TRIP)from 17%to 26%,and twin induced plasticity(TWIP)from 26%to 37%.The yield strength,ultimate tensile strength,and elongation of the fine-grained CS-HEA were 503 MPa,1120 MPa,and 37%,respectively.The strength-ductility synergy of fine-grained CS-HEA was attributed to the combined effects of TRIP,TWIP,dislocation strengthening,and fine-grained strengthening.
基金financially supported by the National Science and Technology Major Project of China(No.2017-Ⅵ-0008-0078)。
文摘Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.
基金supported by the SP2024/089 Project by the Faculty of Materials Science and Technology,VˇSB-Technical University of Ostrava.
文摘In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot always provide sufficiently reliable solutions.Nevertheless,Machine Learning(ML)techniques,which offer advanced regression tools to address complicated engineering issues,have been developed and widely explored.This study investigates the selected ML techniques to evaluate their suitability for application in the hot deformation behavior of metallic materials.The ML-based regression methods of Artificial Neural Networks(ANNs),Support Vector Machine(SVM),Decision Tree Regression(DTR),and Gaussian Process Regression(GPR)are applied to mathematically describe hot flow stress curve datasets acquired experimentally for a medium-carbon steel.Although the GPR method has not been used for such a regression task before,the results showed that its performance is the most favorable and practically unrivaled;neither the ANN method nor the other studied ML techniques provide such precise results of the solved regression analysis.
基金Shenzhen Science and Technology Program(KJZD20230923113900001)Project of Industry and Information Technology Bureau of Shenzhen Municipality(201806071403422960)。
文摘The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.
文摘Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microstructure of the characterization region was analyzed to investigate the recrystallization behavior of 23Cr-8Ni steel.Results show that as the strain rate decreases and the deformation temperature increases,the flow stress decreases.Because the softening phenomenon occurs after the peak stress,the flow stress decreases.The stress index(n)is 4.28,and the thermal deformation activation energy(Q)is 588878 J/mol.Processing map is established,and an optimal thermal processing range of 0.001–0.1 s^(−1) and 1000–1200℃ is achieved,therefore greatly promoting the yield rate.
基金supported by the Natural Science Foundation of Heilongjiang Province,China(No.LH2021E051)the National Natural Science Foundation of China(No.52204386)Outstanding Youth Science Fund of Heilongjiang,China(No.JQ2023E003).
文摘The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this study,single and dual-phase Ni_(55+x)Mn_(25)Ga_(20-x)(x=0,2,4 and 6)alloys were fabricated.The proportion of theγphase was elevated gradually,and the peak martensitic transformation temperature was enhanced from 350 to 460℃ with an increasing Ni/Ga ratio.The microstructures of theγphase were further regulated from continuous block to dispersed granular after annealing.The annealed dual-phase alloy with x=2 exhibited greater yield stress,compressive strength and toughness than the annealed single-phase alloy.It maintained plastic deformation without fracture,even at a strain of 30%.High strain energy and dislocation density were observed in the martensite of the dual-phase alloy,which can be attributed toγphases and the interface between martensite andγphases.Furthermore,[001]-oriented martensite variants were obtained during deformation in the dual-phase alloy.They were parallel to the loading direction and conducive to improving the compressive strength.This protocol provides in-depth insight into the influence of theγphase on the texture evolution and mechanical behavior of martensite during deformation.
基金funded by the Jilin Provincial Department of Science and Technology Fund Project 20240404049ZPthe National Key R and D Program of China(2022YFA1604000)+5 种基金the National Science Fund for Distinguished Young Scholars(51925504)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(52021003)the National Natural Science Foundation of China 52075220the China Postdoctoral Science Foundation Funded Project 2024M751087the Postdoctoral Fellowship Program of CPSF under Grant GZC20230946the Open Research Project of the State Key Laboratory of Strength and Vibration of Mechanical Structures SV2024-KF-13.
文摘Bamboo is an important building material with natural hygroscopicity,and the mechanism of water effects on its deformation and fracture behavior has not been fully revealed.For this purpose,a novel in-situ testing method was developed in this study,which coupled Acoustic Emission(AE)and Digital Image Correlation(DIC)techniques.This method was used to investigate the effects of various Moisture Content(MC)levels(0,6%,15%,and 25%)on the tensile behavior of bamboo.The results showed that as the MC increased from 0 to 25%,the tensile strength of bamboo decreased from 163 to 110 MPa,the Young's modulus dropped from 8.5 to 3.9 GPa,and the elongation increased from 4.3 to 14%.An increase in MC could effectively promote the occurrence of subcritical cracks and micro-interfacial dissociations in bamboo.The synergistic effect of these two factors facilitated strain dispersion,ensuring adaptability to large deformations.Additionally,it was found that an increase in MC could significantly alter the fracture mode.This ingenious synergistic effect in bamboo was revealed for the first time in this study.The mechanisms discovered in this study may provide some important insights into the design and fabrication of advanced biomimetic heterostructures and biomimetic interfacial materials.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIP)(Nos.NRF-2021R1A2C3006662,NRF-2022R1A5A1030054,and RS-2023-00281246)supported by the Basic Science Research Program‘Fostering the Next Generation of Researchers(Ph.D.Candidate)’through the NRF funded by the Ministry of Edu-cation(No.RS-2023-00275651).
文摘Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.
基金supported by the National Research Foundation grant funded by the Korean government(No,2023R1A2C2007190,RS-2024-00398068)partially funded by the Natural Science Foundation of Shandong Province,China(No.ZR2022QE206).
文摘The effects of solid solution on the deformation behavior of binary Mg-xZn(x=0,1,2 wt%)alloys featuring a designated texture that enables extension twinning under tension parallel to the basal pole in most grains,were investigated using in-situ neutron diffraction and the EVPSC-TDT model.Neutron diffraction was used to quantitatively track grain-level lattice strains and diffraction intensity changes(related to mechanical twinning)in differently oriented grains of each alloy during cyclic tensile/compressive loadings.These measurements were accurately captured by the model.The stress-strain curves of Mg-1 wt%Zn and Mg-2 wt%Zn alloys show as-expected solid solution strengthening from the addition of Zn compared to pure Mg.The macroscopic yielding and hardening behaviors are explained by alternating slip and twinning modes as calculated by the model.The solid solution's influence on individual deformation modes,including basal〈a〉slip,prismatic〈a〉slip,and extension twinning,was then quantitatively assessed in terms of activity,yielding behavior,and hardening response by combining neutron diffraction results with crystal plasticity predictions.The Mg-1 wt%Zn alloy displays distinct yielding and hardening behavior due to solid solution softening of prismatic〈a〉slip.Additionally,the dependence of extension twinning,in terms of the twinning volume fraction,on Zn content exhibits opposite trends under tensile and compressive loadings.
基金financially supported by the Technology Area Fund of the Basic Strengthening Program(No.2021-JCJQ-JJ-0092)the Science Center for Gas Turbine Project(Project No.P2022-C-Ⅳ-002-001)+2 种基金the Defense Industrial Technology Development Program(No.JCKY2020130C024)the National Key R&D Program of China(Grant No.2021YFB3702503)the National Science and Tech-nology Major Project(No.Y2019-VII-0011-0151).
文摘A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate-high temperatures and high-low stress conditions.The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy,resulting in approximate cubicγ′phases in dendrites and the formation of initial dislocation tangles.After the stress rupture test at 760℃/780 MPa,high content cubicγ′phases,small size of voids as well as preserved dislocation tangles are observed,showing stable structures with high-stress rupture resistance.High content and suitable size of cubicγ′phases,initial dislocation tangles,and L-C locks hinder the dislocation motion,which decreases the minimum strain rate and prolongs life significantly,forming four stress rupture stages.Hence,the defor-mation mechanism is determined by dislocation piled-up onγ/γ′interface,formation of stacking faults inγ′phases,and dislocations shearingγ′phases.However,the microstructure exhibits uneven struc-tures composed of large sizes of raftedγ′phases and voids at 980℃/260 MPa.The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion,resulting in the increase of minimum strain rate,decline of life,and typic three stress rupture stages,even though there are obstacles to dislocation movement caused by dislocation networks.The deformation mecha-nism transforms to form dislocation networks onγ/γ′interface and dislocations shearingγ′phases.Be-sides,the decomposition of carbides on GBs also depends on temperature,which decomposes into harm-ful chain-like M23 C6 carbides at moderate temperatures and reinforced granular-shaped M6 C carbides at high temperatures.The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.
基金Project(52274369)supported by the National Natural Science Foundation of China。
文摘High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.
基金supported by the fund of the National Natural Science Foundation of China(52275322,51875127)。
文摘The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechanisms.Currently,there is a lack of comparison and evaluation regarding the suitability of different types of models.In this study,Mg-Gd-Y-Zr alloy is taken as the research object.The hot deformation behavior of the alloy was studied systematically.Subsequently,Arrhenius model with strain compensation,artificial neural network(ANN)model,and ISV model involving dynamic recrystallization(DRX),dislocation density and grain size evolution were established.ANN model demonstrates a higher level of accuracy in fitting the original stress-strain curves compared to both ISV model and modified Arrhenius model,but ANN model is not suitable for predicting the experimental results outside of the initial database.ISV model considers the impact of microstructure evolution history on stress,making it highly effective in reflecting the mechanical responses under complex loading condition.The established ISV model is embedded in the ABAQUS software,which shows good ability in calculating the mechanical response,dimension,and microstructure evolution information of the component during hot forming.
基金supported by the National basic scientific research projects(JCKY2021204A004)the National Ministries and Commissions Projects(2019-112hbz)the National Natural Science Foundation of China(No.52271113).
文摘Ti750s titanium alloy,a novel high-temperature titanium alloy designed for short-term service at elevated temperatures(700–750℃),has previously lacked comprehensive understanding of its hot processing behavior.In this study,the high-temperature deformation behavior and microstructural evolution of the Ti750s alloy were systematically investigated through thermal simulation compression tests conducted at temperatures ranging from 900 to 1070℃and strain rates between 0.1 and 10 s⁻1.A hot processing map was constructed using the dynamic material model to optimize the hot processing parameters.The results indicated that the optimal processing window was between 1040 and 1070℃with a strain rate of 0.1 s⁻1.Processing within the instability region resulted in localized plastic deformation,manifesting as pronounced shear bands and a highly heterogeneous strain distribution;this region should be avoided during hot deformation.Within theα+βphase safety zone characterized by low power dissipation rates between 0.32 and 0.4,the primary deformation mechanism in this region was dynamic recovery(DRV),where the lamellarαgrains underwent deformation and rotation.Conversely,in theα+βphase safety zone with high-power dissipation rates between 0.45 and 0.52,dynamic spheroidization of theαphase and dynamic recrystallization(DRX)of theβphase occurred concurrently.In theβphase safety zone with low power dissipation rates between 0.32 and 0.51,the primary deformation mechanism consisted of DRV ofβgrains,accompanied by limited DRX.However,in theβphase safety zone with high-power dissipation rates exceeding 0.56,both DRV and DRX ofβgrains took place,resulted in a significant increase in the size and number of recrystallized grains compared to those observed under low power dissipation conditions.
基金supported by the National Key Research and Development Program of China(No.2022YFF0609000)the National Natural Science Foundation of China(Nos.52171034 and 52101037)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944).
文摘Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.
基金support was received from National Key Research and Development Plan from China:Demonstration and application of special steel for typical components of high-end equipment(2017YFB0703004).
文摘As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.
基金supported by the National Natural Science Foundation of China(nos.52201119,52371108)Frontier Exploration Project of Longmen Laboratory,China(no.LMQYTSKT014)The Joint Fund of Henan Science and Technology R&D Plan of China(no.242103810056).
文摘The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced nonlinearity and multi-scale complexity.This study systematically investigates the hot deformation behavior of Mg-Y-Nd-(Sm)-Zr alloys.Sm alloying promotes recrystallization.The flow stress of Sm-containing alloys declines sharply towards a steady state after reaching its peak value.To overcome the limitations of the Arrhenius-type constitutive(AC)model in predicting complex nonlinear flow behavior,the AC and data hybrid informed neural network(ACINN)model is developed.This approach enhances the predictive accuracy and extends the applicability of the traditional AC model.The evolution of microstructure and recrystallization behavior under hot deformation conditions are investigated based on results from electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The relationship between the power dissipation factor(η)and recrystallization behavior is further examined using K-means clustering analysis.The results demonstrate that dynamic recrystallization(DRX)behavior varies with theηvalue,comprising four distinct regimes:dynamic recovery(DRV),discontinuous dynamic recrystallization(DDRX)dominance,continuous dynamic recrystallization(CDRX)dominance and complete dynamic recrystallization.This analysis presents a new perspective for studying the hot deformation processes of Mg alloys.
基金supported by the National Natural Science Foundation of China(U23A20626)the Key Research and Devel-opment Program of Shandong Province(2021ZLGX01)the Project of Colleges and Universities Innovation Team of Jinan City(2021GXRC030).
文摘The low cycle fatigue(LCF)behaviors and cyclic deformation mechanisms of 2195 Al-Li alloy were inves-tigated under low temperatures(-20℃and-80℃)and different strain amplitudes(0.6%,0.7%,0.8%,and 1.0%).The LCF stress responses under conditions of-20℃&0.6%and-80℃&0.6%exhibited initial cyclic hardening followed by cyclic softening.In contrast,the alloy under other LCF conditions displayed continuous cyclic softening.Notably,the alloy demonstrated reduced LCF life under conditions of-80℃and various strain amplitudes.The fatigue life model based on the total strain energy was developed and proven to be more accurate in predicting fatigue life under diverse LCF conditions.Furthermore,the combined kinematic/isotropic hardening constitutive model exhibited excellent performance in simulat-ing hysteresis loops of the alloy,with corresponding calibration errors all below 14%.Additionally,fatigue fracture surfaces under various LCF conditions consistently exhibited prominent cleavage fracture char-acteristics,and the final fracture zone at-80℃showed increased surface roughness.Finally,the cyclic softening mechanisms were found to be dependent on LCF conditions.The debonding of the interface be-tween the T1 phases and the Al matrix was identified as the primary cyclic softening mechanism under conditions of-20℃&0.6%and-80℃&0.6%.Moreover,the cyclic softening effect under-80℃&1.0%was closely associated with localized shearing of T1 phases.Under-20℃&1.0%,a more pronounced cyclic softening behavior was observed,which was primarily attributed to the continuous shearing of T1 phases.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171013 and 52130110)the Key Research and Development Program of Shaanxi(Grant No.2025CY-YBXM-127)+1 种基金the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0369)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)China(Grant No.2023-QZ-03)。
文摘Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(σ_(y))of BCC Fe can be enhanced by increasing the strain rate(ε)and/or decreasing the deformation temperature(T).With the strain rate increasing from ε=10^(2)s^(-1)to 10^(6) s^(-1),the yield strength at 300 K rises from σ_(y)=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength at σ_(y)=10^(3) s^(-1)decreases from σ_(y)=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,ε>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.
基金financial support from the National Key R&D Program of China(No.2024YFB3713604)the Beijing Municipal Special Program for Science and Technology Service Industry(No.F20241219170567).
文摘During the fabrication of large parts by forging,dynamic recrystallization(DRX)is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel,and an in-depth analysis of this process is necessary.The isothermal hot compression tests were conducted to investigate the hot deformation behavior of Fe-21Cr-15Ni-5Mn-2Mo steel,a novel austenitic stainless steel,at strain rates from 0.01 to 10 s^(-1)and temperatures ranging from 950 to 1200℃.Based on the true stress-strain curves derived from the tests,the constitutive model and hot working map for the steel were constructed,and the microstructure evolution of the steel was systematically analyzed.The critical deformation conditions for the occurrence of DRX were determined using the plotted work hardening rate curve.The findings indicate a significant rise in flow stress as strain rate increases or deformation temperature decreases.Concurrently,the strain needed to attain peak stress progressively grows.The activation energy for deformation of the steel is 595.511 kJ/mol,which results from the competition between dynamic softening and work hardening during its hot deformation process.Low strain rate and low temperature(0.01 s^(-1),950℃)are the parameters for the instability zone of the steel,and localized flow and deformation bands are the microstructure manifestations of unstable hot processing.The optimal hot working window for the experimental steel is the medium to high strain rate range and medium to high temperature(0.1−10 s^(-1),1100−1200℃),where the microstructure exhibits randomly oriented,uniformly distributed DRX grains.The bulging of the initial grain boundaries is primarily associated with the nucleation mechanism of DRX.Furthermore,based on the critical strain and peak strain,the kinetics of DRX are predicted by the Avrami equation.
基金Project(IRT0713) supported by the Program for Changjiang Scholars and Innovative Research Team in Chinese UniversityProjects(2007CB613701,2007CB613702) supported by the National Basic Research Program of China
文摘The effects of plastic deformation on precipitation behavior and tensile fracture behavior of Mg-10Gd-3Y-0.6Zr alloy were investigated.The results indicate that more precipitation cores can be provided by the crystal defects caused by the plastic deformation,as well as increasing the amount of β＇ phases,and the formation of precipitations at grain boundaries and interfaces between the twins and matrix.Because of an increase in precipitations,the dislocation slipping during deformation process is effectively hindered and the matrix is strengthened,especially for the 2% deformed alloy which can achieve a good combination of strength and ductility.With increasing the plastic deformation,the microcracks occur at the interface between grain boundary precipitations and matrix,and then propagate intergranularly.When intergranular fracture combines with the formation of smoothing facets on the fracture surface,the tensile properties decrease.
