Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behav...Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behavior and mechanical response of the as-rolled and annealed samples were systematically investigated by a combination of electron microscopy and microhardness characterization.The results show that the twinning activities were highly suppressed in the fine-grained samples during rolling.Upon increasing the rolling reduction to 40%,ultra-fine grain structures with a volume fraction of∼28%were formed due to the activation of multiple slip systems.Conversely,twinning dominated the early stages of deformation in the coarse-grained samples.After a 10%rolling reduction,numerous twins with a volume fraction of∼23%were formed.Further increasing the rolling reduction to 40%,high-density dislocations were activated and twin structures with a volume fraction of∼36%were formed.The annealing hardening response of deformed samples was effectively enhanced compared to that of the non-deformed samples,which was attributed to the enhanced Gd segregation along grain boundaries,twin boundaries and dislocation cores.Moreover,the grain size and rolling reduction were found to affect the microstructure evolution during annealing,resulting in a notable difference in the annealing hardening response of Mg-3Gd alloy between samples of different grain sizes deformed to different strains.These findings highlight the crucial importance of microstructural and processing parameters in the design of high-strength,cost-effective Mg alloys.展开更多
In order to clarify the influence of grain size on cyclic deformation response of superalloy sheets and springback behavior,cyclic loading-unloading and shearing tests were performed on the superalloy foils with 0.2 m...In order to clarify the influence of grain size on cyclic deformation response of superalloy sheets and springback behavior,cyclic loading-unloading and shearing tests were performed on the superalloy foils with 0.2 mm in thickness and diverse grain sizes.The results show that,the decline ratio of elastic modulus is weakened with increasing grain size,and the Bauschinger effect becomes evident with decreasing grain size.Meanwhile,U-bending test results determine that the springback is diminished with increasing grain size.The Chaboche,Anisotropic Nonlinear Kinematic(ANK)and Yoshida-Uemori(Y-U)models were utilized to fit the shear stress-strain curves of specimens.It is found that Y-U model is sufficient of predicting the springback.However,the prediction accuracy is degraded with increasing grain size.展开更多
The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high deman...The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application.To achieve this objective,this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process.Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction(EBSD),Scanning Electron Microscopy(SEM),X-Ray Diffraction(XRD),High-Resolution Transmission Electron Microscopy(HRTEM),and Focused Ion Beam(FIB).Besides,the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests.The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one,primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam.The effects of grain size,such as pinning and splitting,are amplified at higher brazing temperatures.Additionally,micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone,leading to a cleavage fracture mode.The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path.Therefore,this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.展开更多
Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si...Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.展开更多
Barium titanate[BaTiO_(3)(BT)]-based ceramics are typical ferroelectric materials.Here,the discontinuous grain growth(DGG)and relevant grain size effect are deeply studied.An obvious DGG phenomenon is observed in a pa...Barium titanate[BaTiO_(3)(BT)]-based ceramics are typical ferroelectric materials.Here,the discontinuous grain growth(DGG)and relevant grain size effect are deeply studied.An obvious DGG phenomenon is observed in a paradigmatic Zr^(4+)-doped BT-based ceramic,with grains growing from∼2.2–6.6 to∼121.8–198.4μm discontinuously near 1320℃.It is found that fine grains can get together and grow into large ones with liquid phase surrounding them above eutectic temperature.Then the grain boundary density(D g)is quantitatively studied and shows a first-order reciprocal relationship with grain size,and the grain size effect is dependent on D g.Fine grains lead to high D g,and then cause fine domains and pseudocubic-like phase structure because of the interrupted long-range ferroelectric orders by grain boundary.High D g also causes the diffusion phase transition and low Curie dielectric peak due to the distribution of phase transition temperature induced by internal stress.Local domain switching experiments reveal that the polarization orientation is more difficult near the grain boundary,implying that the grain boundary inhibition dominates the process of polarization orientation in fine-grain ceramics,which leads to low polarization but a high coercive field.However,large-grain ceramics exhibit easy domain switching and high&similar ferroelectricity.This work reveals that the grain boundary effect dominates the grain size effect in fine-grain ceramics,and expands current knowledge on DGG and grain size effect in polycrystalline materials.展开更多
The grain size of Mg foams was innovatively refined without alteration of pore structure and relative density by subjecting multi-axial forging(MAF)process to Ti-Mg composite,an intermediary product of the fabrication...The grain size of Mg foams was innovatively refined without alteration of pore structure and relative density by subjecting multi-axial forging(MAF)process to Ti-Mg composite,an intermediary product of the fabrication process of Mg foams where the spherical Ti particles were utilized as the replication material.The feasibility of the MAF process and the grain size effect on the mechanical properties of Mg foams were discussed.The results showed that,with the appropriate strain of 0.24 applied in the MAF process,Ti-Mg composites returned to original physical appearance without generating microcracks.And complete recrystallization was achieved after heat treatment,with the grain size of the MAFprocessed Mg foams two to three orders of magnitude smaller than that of as-cast foam.The mechanical properties of Mg foams were enhanced extensively after grain refinement with the yield strength and the plastic collapse strength increased by 147%and 50.7%,respectively.A revised model integrated by the Hall-Petch law and Gibson-Ashby model was proposed,which gave a good estimation of the yield strength and the plastic collapse strength of Mg foams from the compressive behavior of the corresponding parent material,though a knockdown factor of 0.45 was introduced for the yield strength.展开更多
Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of eff...Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant K_(eff) on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material K_(eff) decreases with the reduction of grain size. The variation of K_(eff) is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd_2Fe_(14)B permanent magnetic material.展开更多
X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very impo...X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographic parameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The results show that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio of high angle grain boundary to small angle grain boundary are important parameters. The finer the effective grain size, and the higher the frequency distribution of grain boundaries （〉 50~）, the more excellent toughness of high grade pipeline steels will be.展开更多
The effect of cooling rate on microstructure and effective grain size(EGS)of a Ni-Cr-Mo-B high-strength steel has been studied by dilatometer,field emission scanning electron microscopy(FESEM),transmission electron mi...The effect of cooling rate on microstructure and effective grain size(EGS)of a Ni-Cr-Mo-B high-strength steel has been studied by dilatometer,field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM)and electron backscattered diffraction(EBSD).The results show that the microstructure of the Ni-Cr-Mo-B steel is dependent on cooling rate in the following sequence:lath martensite(LM),mixed LM and lath bainite(LB),mixed LB and granular bainite(GB)and GB.The critical cooling rates for appearance of LB and GB are about 10℃/s and 0.5℃/s,respectively.The LM(>10℃/s)consists of few blocky regions with a width of several micros.Compared with the lath regions,the blocky regions in LM form at higher actual transformation temperatures during cooling.The blocky region area percentage in LM keeps almost constant about 8%at different cooling rates(>10℃/s)due to similar martensite transformation starting temperature(M_(s)).The LB percentage in mixed LM/LB increases gradually with decreasing cooling rate(10-0.5℃/s).The EBSD results show that different microstructures have different EGS.The mixed LM/LB exhibits the smallest EGS due to the separation of the prior austenite grains by the pre-formed LB and the refinement of the LM.Meanwhile,the mixed LM/LB at different cooling rates(10-0.5℃/s)exhibits almost the same EGS because the LB and LM in the mixed LM/LB have a similar high-angle grain boundary density and similar EGS.Because the blocky regions contain few high-angle grain boundaries and have similar area percentages in the LM,the LM at different cooling rates(>10℃/s)exhibits almost the same EGS.The ferrite in GB exhibits as a whole with few high-angle grain boundaries;thus,the mixed LB/GB exhibits the largest EGS.展开更多
The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the...The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.展开更多
To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the dep...To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.展开更多
Through molecular dynamics（MD） simulation, the dependencies of temperature, grain size and strain rate on the mechanical properties were studied. The simulation results demonstrated that the strain rate from 0.05 to...Through molecular dynamics（MD） simulation, the dependencies of temperature, grain size and strain rate on the mechanical properties were studied. The simulation results demonstrated that the strain rate from 0.05 to 2 ns–1 affected the Young＇s modulus of nickel nanowires slightly, whereas the yield stress increased. The Young＇s modulus decreased approximately linearly; however, the yield stress firstly increased and subsequently dropped as the temperature increased. The Young＇s modulus and yield stress increased as the mean grain size increased from 2.66 to 6.72 nm. Moreover, certain efforts have been made in the microstructure evolution with mechanical properties association under uniaxial tension. Certain phenomena such as the formation of twin structures, which were found in nanowires with larger grain size at higher strain rate and lower temperature, as well as the movement of grain boundaries and dislocation, were detected and discussed in detail. The results demonstrated that the plastic deformation was mainly accommodated by the motion of grain boundaries for smaller grain size. However, for larger grain size, the formations of stacking faults and twins were the main mechanisms of plastic deformation in the polycrystalline nickel nanowire.展开更多
In the present study,room-temperature compression experiments and characterization experiments via optical microstructure(OM),X-ray diffractometer(XRD)and electron backscattered diffraction(EBSD)techniques were conduc...In the present study,room-temperature compression experiments and characterization experiments via optical microstructure(OM),X-ray diffractometer(XRD)and electron backscattered diffraction(EBSD)techniques were conducted on WE43 magnesium(Mg)alloy samples to investigate the grain size effect on twinning behavior.Three couples of solution treatments(823 K for 0.5 h,798 K for 8 h,823 K for 16 h,followed by water-quenching at~333 K)were adopted and these solutionized samples are with different grain sizes of 48.5,72.0 and 120.2μm,respectively.Results show that{10-12}extension twin(ET)and{11-21}ET serve as major twinning modes during plastic deformation.For all 7.7%-deformed samples,although the volume fractions of{10-12}ETs and{11-21}ETs increase with the increasing grain size.{10-12}ETs are in growth stage,while{11-21}ETs are mainly in nucleation stage and they still maintain narrow and parallel to each other.Besides,{10-12}ETs mainly contribute to the rotation of caxes of grains towards compression direction,while{11-21}ETs mainly contribute to the formation of a nearly ring-shaped texture component in(0002)pole figure.Twin variants analysis with the assistance of Schmid factor(SF)demonstrates that the activation of twin variants mainly obeys Schmid law.When only{10-12}ETs occur in individual grains,the maximum number of twin variants shows some positive relationship with the increasing grain size.By comparison,when both{10-12}ETs and{11-21}ETs occur in individual grains,the maximum numbers of twin variants are rarely influenced by the increasing grain size.展开更多
GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crac...GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached 10 times the grain size.展开更多
This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain ...This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate(4×10~9 s^(-1)),while the temperature and initial pressure remained 300 K and 0 bar,respectively.It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials,which was vividly characterized by void nucleation,growth,and coalescence.The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes.Interestingly,it was discovered that the void evolution was characteristic of an almost double-linear behavior,and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size.More importantly,the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy.For small grain size,the existing voids propagated along the grain boundaries and in the grains,leading to intergranular and transgranular fracture.Contrarily,the intergranular-dominated fracture was responsible for the void propagation in the large grain.In addition,the starting time,ending time,and threshold of void nucleation were found to be weak sensitivity to GS,and a reverse effect was appropriate to the void growth.The results highlighted that as the GS increased,more complete stress relaxation and shorter duration time were produced,leading to larger void volume fraction and faster growth rate.展开更多
Size effects make traditional forming theories infeasible in analyzing the micro-forming process, so it is necessary to develop an accurate material model to describe the material flow behavior with consideration of s...Size effects make traditional forming theories infeasible in analyzing the micro-forming process, so it is necessary to develop an accurate material model to describe the material flow behavior with consideration of size effects. By studying the size effects of the flow behavior of H80 foils experimentally, it is found that the foil flow stress and strain hardening ability reduce significantly with the decrease of foil thickness. The reduction of the proportion of internal grains which own complete grain boundaries is the main cause of size effects of foil flow behavior. Moreover, grain refinement can reduce the size effects on material flow behavior. On these bases, a phenomenological material model has been developed to mathematically describe the material flow behavior with consideration of the effects of geometry size, grain size and strain hardening behavior. The reasonability and accuracy of this new model are verified by comparing the calculation values with experimental results in metal foil tensile and micro-bulk upsetting experiments. These experimental results and the proposed model lay a solid foundation for understanding and further exploring the material flow behavior in the micro-forming process.展开更多
The influence of grain size and ordering degree of the parent phase on the shape memory re- covery in a Cu-25.62Zn-3.97Al-0.0018B(wt-%)memory alloy is investigated.A mathematical relationship is set up between the rec...The influence of grain size and ordering degree of the parent phase on the shape memory re- covery in a Cu-25.62Zn-3.97Al-0.0018B(wt-%)memory alloy is investigated.A mathematical relationship is set up between the recovery ratio and ordering degree,probabili- ty of atoms at their ordered sites,grain size,the thickness of the grain boundary affected re- gions,the stress during deformation,as well as the critical shear stress.Shape memory effect reaches a maximum with varying grain size and increases linearly with increasing ordering parameter,which agrees well with experimental results.展开更多
Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its...Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.展开更多
The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat ...The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine as precipitates and continuous α_(s) played greater roles than other features,resulting in a high strength and very low ductility(<2%)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA( β anneal slow cooling and ageing)process,improved ductility and fracture toughness were obtained due to a lower density ofα;precipitates,a basket-weave structure and zigzag morphology of α_(GB).For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.展开更多
基金financial support from the National Key Research and Development Program of China(No.2021YFB3702101)National Natural Science Foundation of China(No.52130107,52071038)+5 种基金Fundamental Research Funds for the Central Universities(No.2023CDJXY-018)the“111”Project(No.B16007)by the Ministry of Education and the State Administration of Foreign Experts Affairs of Chinasupport to the Norwegian Micro-and Nano-Fabrication Facility,NorFab(No.295864)the Norwegian Laboratory for Mineral and Materials Characterization,MiMaC(No.269842/F50)the RCN INRPART project IntMat(No.309724)the Center for Research based Innovation SFI PhysMet(No.309584).
文摘Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behavior and mechanical response of the as-rolled and annealed samples were systematically investigated by a combination of electron microscopy and microhardness characterization.The results show that the twinning activities were highly suppressed in the fine-grained samples during rolling.Upon increasing the rolling reduction to 40%,ultra-fine grain structures with a volume fraction of∼28%were formed due to the activation of multiple slip systems.Conversely,twinning dominated the early stages of deformation in the coarse-grained samples.After a 10%rolling reduction,numerous twins with a volume fraction of∼23%were formed.Further increasing the rolling reduction to 40%,high-density dislocations were activated and twin structures with a volume fraction of∼36%were formed.The annealing hardening response of deformed samples was effectively enhanced compared to that of the non-deformed samples,which was attributed to the enhanced Gd segregation along grain boundaries,twin boundaries and dislocation cores.Moreover,the grain size and rolling reduction were found to affect the microstructure evolution during annealing,resulting in a notable difference in the annealing hardening response of Mg-3Gd alloy between samples of different grain sizes deformed to different strains.These findings highlight the crucial importance of microstructural and processing parameters in the design of high-strength,cost-effective Mg alloys.
基金the National Natural Science Foundation of China(Nos.51975031,52075023,51635005)Defense Industrial Technology Development Program,China(No.JCKY2018601C207)。
文摘In order to clarify the influence of grain size on cyclic deformation response of superalloy sheets and springback behavior,cyclic loading-unloading and shearing tests were performed on the superalloy foils with 0.2 mm in thickness and diverse grain sizes.The results show that,the decline ratio of elastic modulus is weakened with increasing grain size,and the Bauschinger effect becomes evident with decreasing grain size.Meanwhile,U-bending test results determine that the springback is diminished with increasing grain size.The Chaboche,Anisotropic Nonlinear Kinematic(ANK)and Yoshida-Uemori(Y-U)models were utilized to fit the shear stress-strain curves of specimens.It is found that Y-U model is sufficient of predicting the springback.However,the prediction accuracy is degraded with increasing grain size.
基金co-supported by the National Natural Science Foundation of China(No.52105316)the National Natural Foundation of Jiangxi,China(No.2021BAB214046)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.501LKQB2022107021)Young Elite Scientists Sponsorship Program by the China Association for Science and Technology(No.YESS20200397)。
文摘The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application.To achieve this objective,this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process.Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction(EBSD),Scanning Electron Microscopy(SEM),X-Ray Diffraction(XRD),High-Resolution Transmission Electron Microscopy(HRTEM),and Focused Ion Beam(FIB).Besides,the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests.The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one,primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam.The effects of grain size,such as pinning and splitting,are amplified at higher brazing temperatures.Additionally,micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone,leading to a cleavage fracture mode.The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path.Therefore,this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.
基金financially supported by the National Natural Science Foundation of China (No. 51771147)
文摘Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.
基金financially supported by the National Natu-ral Science Foundation of China(Nos.12104093,52072075,and 52102126)the Natural Science Foundation of Fujian Province(Nos.2021J05122,2021J05123,2022J01087,and 2022J01552)+2 种基金the Sichuan Province Science and Technology Support Program(No.2021YJ0560,22ZDYF3306,2022NSFSC1970,and 2022YFG0099)the Qishan Scholar Financial Support from Fuzhou University(No.GXRC-20099)the Fundamental Research Funds for the Central Universities,Southwest Minzu University(No.2020NTD03).
文摘Barium titanate[BaTiO_(3)(BT)]-based ceramics are typical ferroelectric materials.Here,the discontinuous grain growth(DGG)and relevant grain size effect are deeply studied.An obvious DGG phenomenon is observed in a paradigmatic Zr^(4+)-doped BT-based ceramic,with grains growing from∼2.2–6.6 to∼121.8–198.4μm discontinuously near 1320℃.It is found that fine grains can get together and grow into large ones with liquid phase surrounding them above eutectic temperature.Then the grain boundary density(D g)is quantitatively studied and shows a first-order reciprocal relationship with grain size,and the grain size effect is dependent on D g.Fine grains lead to high D g,and then cause fine domains and pseudocubic-like phase structure because of the interrupted long-range ferroelectric orders by grain boundary.High D g also causes the diffusion phase transition and low Curie dielectric peak due to the distribution of phase transition temperature induced by internal stress.Local domain switching experiments reveal that the polarization orientation is more difficult near the grain boundary,implying that the grain boundary inhibition dominates the process of polarization orientation in fine-grain ceramics,which leads to low polarization but a high coercive field.However,large-grain ceramics exhibit easy domain switching and high&similar ferroelectricity.This work reveals that the grain boundary effect dominates the grain size effect in fine-grain ceramics,and expands current knowledge on DGG and grain size effect in polycrystalline materials.
基金supported financially by the National Key Research and Development Program of China(No.2016YFC1102103)the Shanghai Municipal Commission of Economy and Informatization(No.JJ-YJCX-01-19-1277)+1 种基金the Science and Technology Commission of Shanghai Municipality(Nos.19441906300,19441913400,18441908000 and 17440730700)the Shanghai Rising-Star Program(No.19QB1400400)。
文摘The grain size of Mg foams was innovatively refined without alteration of pore structure and relative density by subjecting multi-axial forging(MAF)process to Ti-Mg composite,an intermediary product of the fabrication process of Mg foams where the spherical Ti particles were utilized as the replication material.The feasibility of the MAF process and the grain size effect on the mechanical properties of Mg foams were discussed.The results showed that,with the appropriate strain of 0.24 applied in the MAF process,Ti-Mg composites returned to original physical appearance without generating microcracks.And complete recrystallization was achieved after heat treatment,with the grain size of the MAFprocessed Mg foams two to three orders of magnitude smaller than that of as-cast foam.The mechanical properties of Mg foams were enhanced extensively after grain refinement with the yield strength and the plastic collapse strength increased by 147%and 50.7%,respectively.A revised model integrated by the Hall-Petch law and Gibson-Ashby model was proposed,which gave a good estimation of the yield strength and the plastic collapse strength of Mg foams from the compressive behavior of the corresponding parent material,though a knockdown factor of 0.45 was introduced for the yield strength.
基金Project supported by National‘863’Project (2002AA324050 2002AA302602) and Natural Science Foundation of China(50371046) and Doctoral Foundation of China (20040422014)
文摘Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant K_(eff) on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material K_(eff) decreases with the reduction of grain size. The variation of K_(eff) is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd_2Fe_(14)B permanent magnetic material.
基金Funded by China Postdoctoral Science Foundation(No.20060390319)
文摘X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographic parameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The results show that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio of high angle grain boundary to small angle grain boundary are important parameters. The finer the effective grain size, and the higher the frequency distribution of grain boundaries （〉 50~）, the more excellent toughness of high grade pipeline steels will be.
基金financially supported by the Liaoning Revitalization Talents Program(No.XLYC1907143)the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDC04000000 and XDA28040200)。
文摘The effect of cooling rate on microstructure and effective grain size(EGS)of a Ni-Cr-Mo-B high-strength steel has been studied by dilatometer,field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM)and electron backscattered diffraction(EBSD).The results show that the microstructure of the Ni-Cr-Mo-B steel is dependent on cooling rate in the following sequence:lath martensite(LM),mixed LM and lath bainite(LB),mixed LB and granular bainite(GB)and GB.The critical cooling rates for appearance of LB and GB are about 10℃/s and 0.5℃/s,respectively.The LM(>10℃/s)consists of few blocky regions with a width of several micros.Compared with the lath regions,the blocky regions in LM form at higher actual transformation temperatures during cooling.The blocky region area percentage in LM keeps almost constant about 8%at different cooling rates(>10℃/s)due to similar martensite transformation starting temperature(M_(s)).The LB percentage in mixed LM/LB increases gradually with decreasing cooling rate(10-0.5℃/s).The EBSD results show that different microstructures have different EGS.The mixed LM/LB exhibits the smallest EGS due to the separation of the prior austenite grains by the pre-formed LB and the refinement of the LM.Meanwhile,the mixed LM/LB at different cooling rates(10-0.5℃/s)exhibits almost the same EGS because the LB and LM in the mixed LM/LB have a similar high-angle grain boundary density and similar EGS.Because the blocky regions contain few high-angle grain boundaries and have similar area percentages in the LM,the LM at different cooling rates(>10℃/s)exhibits almost the same EGS.The ferrite in GB exhibits as a whole with few high-angle grain boundaries;thus,the mixed LB/GB exhibits the largest EGS.
基金Project(2023YFC2907403)supported by the National Key R&D Program of ChinaProject(52074021)supported by the National Natural Science Foundation of China+1 种基金Project(2242045)supported by Beijing Natural Science Foundation,ChinaProject(ZD202216)supported by the Beijing Association of Higher Education,China。
文摘The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.
基金supported by the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDB0510400)the National Natural Science Foundation of China(No.52225102)the Youth Innovation Promotion Association CAS(No.2023201).
文摘To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.
基金Supported by the National Natural Science Foundation of China(11102139,11472195)the Natural Science Foundation of Hubei Province of China(2014CFB713)
文摘Through molecular dynamics（MD） simulation, the dependencies of temperature, grain size and strain rate on the mechanical properties were studied. The simulation results demonstrated that the strain rate from 0.05 to 2 ns–1 affected the Young＇s modulus of nickel nanowires slightly, whereas the yield stress increased. The Young＇s modulus decreased approximately linearly; however, the yield stress firstly increased and subsequently dropped as the temperature increased. The Young＇s modulus and yield stress increased as the mean grain size increased from 2.66 to 6.72 nm. Moreover, certain efforts have been made in the microstructure evolution with mechanical properties association under uniaxial tension. Certain phenomena such as the formation of twin structures, which were found in nanowires with larger grain size at higher strain rate and lower temperature, as well as the movement of grain boundaries and dislocation, were detected and discussed in detail. The results demonstrated that the plastic deformation was mainly accommodated by the motion of grain boundaries for smaller grain size. However, for larger grain size, the formations of stacking faults and twins were the main mechanisms of plastic deformation in the polycrystalline nickel nanowire.
基金Project supported by the Natural Science Foundation of Chongqing(CSTB2022NSCQ-MSX0252)Research and Innovation Team Cultivation Project of Chongqing University of Technology(2023TDZ010)。
文摘In the present study,room-temperature compression experiments and characterization experiments via optical microstructure(OM),X-ray diffractometer(XRD)and electron backscattered diffraction(EBSD)techniques were conducted on WE43 magnesium(Mg)alloy samples to investigate the grain size effect on twinning behavior.Three couples of solution treatments(823 K for 0.5 h,798 K for 8 h,823 K for 16 h,followed by water-quenching at~333 K)were adopted and these solutionized samples are with different grain sizes of 48.5,72.0 and 120.2μm,respectively.Results show that{10-12}extension twin(ET)and{11-21}ET serve as major twinning modes during plastic deformation.For all 7.7%-deformed samples,although the volume fractions of{10-12}ETs and{11-21}ETs increase with the increasing grain size.{10-12}ETs are in growth stage,while{11-21}ETs are mainly in nucleation stage and they still maintain narrow and parallel to each other.Besides,{10-12}ETs mainly contribute to the rotation of caxes of grains towards compression direction,while{11-21}ETs mainly contribute to the formation of a nearly ring-shaped texture component in(0002)pole figure.Twin variants analysis with the assistance of Schmid factor(SF)demonstrates that the activation of twin variants mainly obeys Schmid law.When only{10-12}ETs occur in individual grains,the maximum number of twin variants shows some positive relationship with the increasing grain size.By comparison,when both{10-12}ETs and{11-21}ETs occur in individual grains,the maximum numbers of twin variants are rarely influenced by the increasing grain size.
基金ffinancially supported by the National Natural Science Foundations of China (Nos. 51725503, 51605164 and 51575183)the 111 project+3 种基金support by Shanghai Technology Innovation Program of SHEITC (No. CXY-2015-001)Fok Ying Tung Education Foundationsupport by Shanghai Sailing Program (No. 16YF1402300)Shanghai Chenguang Program (No. 16CG34).
文摘GH4169 at 650℃ in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached 10 times the grain size.
基金the financial support of the Natural Science Foundation Project of CQ CSTC under grant number cstc2018jcyjAX0581the Fundamental Research Funds for the Central Universities under grant number XDJK2018B002+1 种基金the foundation of the National Key Defense Laboratory for Computational Physics under grant number HXo2020-74the Venture&Innovation Support Program for Chongqing Overseas Returnees under grant number cx2018078。
文摘This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate(4×10~9 s^(-1)),while the temperature and initial pressure remained 300 K and 0 bar,respectively.It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials,which was vividly characterized by void nucleation,growth,and coalescence.The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes.Interestingly,it was discovered that the void evolution was characteristic of an almost double-linear behavior,and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size.More importantly,the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy.For small grain size,the existing voids propagated along the grain boundaries and in the grains,leading to intergranular and transgranular fracture.Contrarily,the intergranular-dominated fracture was responsible for the void propagation in the large grain.In addition,the starting time,ending time,and threshold of void nucleation were found to be weak sensitivity to GS,and a reverse effect was appropriate to the void growth.The results highlighted that as the GS increased,more complete stress relaxation and shorter duration time were produced,leading to larger void volume fraction and faster growth rate.
基金financially supported by the Foundation of Suzhou University of Science and Technology(No.XKQ2017005)
文摘Size effects make traditional forming theories infeasible in analyzing the micro-forming process, so it is necessary to develop an accurate material model to describe the material flow behavior with consideration of size effects. By studying the size effects of the flow behavior of H80 foils experimentally, it is found that the foil flow stress and strain hardening ability reduce significantly with the decrease of foil thickness. The reduction of the proportion of internal grains which own complete grain boundaries is the main cause of size effects of foil flow behavior. Moreover, grain refinement can reduce the size effects on material flow behavior. On these bases, a phenomenological material model has been developed to mathematically describe the material flow behavior with consideration of the effects of geometry size, grain size and strain hardening behavior. The reasonability and accuracy of this new model are verified by comparing the calculation values with experimental results in metal foil tensile and micro-bulk upsetting experiments. These experimental results and the proposed model lay a solid foundation for understanding and further exploring the material flow behavior in the micro-forming process.
文摘The influence of grain size and ordering degree of the parent phase on the shape memory re- covery in a Cu-25.62Zn-3.97Al-0.0018B(wt-%)memory alloy is investigated.A mathematical relationship is set up between the recovery ratio and ordering degree,probabili- ty of atoms at their ordered sites,grain size,the thickness of the grain boundary affected re- gions,the stress during deformation,as well as the critical shear stress.Shape memory effect reaches a maximum with varying grain size and increases linearly with increasing ordering parameter,which agrees well with experimental results.
基金supported by the National Natural Science Foundation of China(Nos.12372331,12072307,and 12302429)the Science and Technology Innovation Program of Hunan Province,China(No.2024RC3160)the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110116).
文摘Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.
基金the financial support from Baosteel Australia Joint Research Centre(BA16003)ARC Research Hub for Computational Particle Technology(IH140100035)funded by Australian Research Council grant LE0882821。
文摘The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine as precipitates and continuous α_(s) played greater roles than other features,resulting in a high strength and very low ductility(<2%)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA( β anneal slow cooling and ageing)process,improved ductility and fracture toughness were obtained due to a lower density ofα;precipitates,a basket-weave structure and zigzag morphology of α_(GB).For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.
