Effects of alloying elements Ni,Co,Mn,Cr,and H on the stacking fault energy(SFE)ofγ-Fe and its microscopic mechanisms were systematically investigated.Generalized SFE calculations show that individual alloying elemen...Effects of alloying elements Ni,Co,Mn,Cr,and H on the stacking fault energy(SFE)ofγ-Fe and its microscopic mechanisms were systematically investigated.Generalized SFE calculations show that individual alloying elements Ni,Co,and H increase SFE ofγ-Fe,whereas Mn and Cr decrease SFE.The influence of alloying elements on SFE exhibits short-range characteristics.The effect of synergistic interaction of alloying elements and H on SFE was further investigated.Results show that the co-alloying of Ni/Co with H exacerbates the effect of H on the increase in SFE.In contrast,the synergistic effect of Mn/Cr with H tends to inhibit H from the increasing SFE.Finally,the electronic structure analysis elucidated the microscopic mechanism of the change in SFE.Alloying elements modulate SFE by changing the interatomic charge density at the stacking fault plane and the density of states of the stacking fault structure at the Fermi level.The present results add to the knowledge of alloying related influence on the mechanical property and hydrogen embrittlement ofγ-Fe.展开更多
1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifi...1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifice of plastic deformation capability[2].Lately,many strategies have been proposed to improve the comprehensive properties of materials,among which manipulating stacking fault energy(SFE)is effective[3–5].展开更多
High-density stacking faults(SFs)were introduced into a novel Ni-Co-based superalloy through warm rolling at 300-500°C,and the effects of SFs on its tensile properties at intermediate temperatures(650 and 750...High-density stacking faults(SFs)were introduced into a novel Ni-Co-based superalloy through warm rolling at 300-500°C,and the effects of SFs on its tensile properties at intermediate temperatures(650 and 750°C)were investigated.The results indicated that all warm rolled specimens have high-density SFs and Lomer-Cottrell locks compared with the initial specimens.Meanwhile,the simultaneous improvement of intermediate-temperature strength and ductility of alloys can be achieved by high-density SFs.In particular,the specimen rolled at 300°C exhibited a superior combination of high strength(yield and ultimate tensile strengths of(1311±18)and(1462±25)MPa respectively at 650°C,and(1180±17)and(1293±15)MPa respectively at 750°C)and high fracture elongation((26.7±2.5)%at 650°C and(10.7±1.3)%at 750°C).The high strengths and facture elongations of all warm-rolled specimens were primarily attributed to the interaction of pre-existingγ′phases,high-density SFs and Lomer-Cottrell locks with dislocations,as well as to the formation of high-density deformation nano-twins during tensile loading.展开更多
It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Ph...It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Phase transformation,morphology characteristics of nano twins,compressive and tensile proper-ties,and the related mechanisms have been studied.Results show that B2 phase enriched with Re tends to precipitate along theα_(2)/γinterface within lamellar colony.The stacking fault energy(SFE)ofγphase decreases from 43 mJ/m^(2) to 16 mJ/m^(2) as Re content increases from 0 at.%to 0.6 at.%,decreasing the crit-ical shear stress for twin formation.Compared to the mismatch value ofα_(2)/γinterface(0.004),which of B2/α_(2) and B2/γinterfaces increase to 0.247 and 0.149,respectively.Driven by high interfacial stress,high-density dislocations are generated at the B2/α_(2) interface,providing the dislocation slip channel for the formation of stacking faults(SFs)and nanotwins at the B2/γinterface.Therefore,the mechanism of inducting high-density nanotwins is to reduce the stacking fault energy ofγphase by Re and form highly mismatched B2/α_(2) interface.Compressive strength and the strain increase from 1723 MPa to 2398 MPa and 29%to 39%as Re content increases from 0 at.%to 0.6 at.%,respectively.Tensile strength increases from 356 MPa to 452 MPa without sacrificing plasticity.The improvement in strength and plasticity are attributed to the nano-twinning strengthening and interfacial thermal mismatch strengthening.Forming nanotwins during solidification process serve as the nucleation sites for newly formed twins during de-formation process,increasing the deformation tolerance of TiAl alloy.展开更多
To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope...To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.展开更多
Self-powered neutron detectors(SPNDs)play a critical role in monitoring the safety margins and overall health of reactors,directly affecting safe operation within the reactor.In this work,a novel fault identification ...Self-powered neutron detectors(SPNDs)play a critical role in monitoring the safety margins and overall health of reactors,directly affecting safe operation within the reactor.In this work,a novel fault identification method based on graph convolutional networks(GCN)and Stacking ensemble learning is proposed for SPNDs.The GCN is employed to extract the spatial neighborhood information of SPNDs at different positions,and residuals are obtained by nonlinear fitting of SPND signals.In order to completely extract the time-varying features from residual sequences,the Stacking fusion model,integrated with various algorithms,is developed and enables the identification of five conditions for SPNDs:normal,drift,bias,precision degradation,and complete failure.The results demonstrate that the integration of diverse base-learners in the GCN-Stacking model exhibits advantages over a single model as well as enhances the stability and reliability in fault identification.Additionally,the GCN-Stacking model maintains higher accuracy in identifying faults at different reactor power levels.展开更多
Due to the insufficient slip systems,Mg and its alloys exhibit poor ductility during plastic deformation at room temperature.To solve this problem,alloying is considered as a most effective method to improve the ducti...Due to the insufficient slip systems,Mg and its alloys exhibit poor ductility during plastic deformation at room temperature.To solve this problem,alloying is considered as a most effective method to improve the ductility of Mg alloys,which attracts wide attentions of industries.However,it is still a challenge to understand the ductilization mechanism,because of the complicated alloying elements and their interactions with Mg matrix.In this work,pure Mg and Mg-Y alloys were comparatively studied to investigate the effect of Y addition on microstructure evolution and mechanical properties.A huge increase of uniform elongation,from 5.3%to 20.7%,was achieved via only 3 wt%addition of yttrium.TEM results revealed that the only activated slip system in pure Mg was basalslip,led to its poor ductility at room temperature.In contrast,a large number of stacking faults and non-basal dislocations with<c>component were observed in the deformed Mg-Y alloy,which was proposed as the main reason for significant improvement of strain hardening and ductility.High resolution TEM indicated that most of the stacking faults were II and 12 intrinsic faults,which played a critical role in improving the ductility of Mg-Y alloy.Addition of Y into Mg alloy decreased the stacking fault energy,which induced high density stacking faults in the grain interior.展开更多
In order to study the effects of Nd addition on microstructure and mechanical properties of Mg-Gd-Zn-Zr alloys,the microstruc-ture and mechanical properties of the as-cast Mg-12Gd-2Zn-xNd-0.4Zr(x=0,0.5wt%,and 1wt%)all...In order to study the effects of Nd addition on microstructure and mechanical properties of Mg-Gd-Zn-Zr alloys,the microstruc-ture and mechanical properties of the as-cast Mg-12Gd-2Zn-xNd-0.4Zr(x=0,0.5wt%,and 1wt%)alloys were investigated by using optical microscope,scanning electron microscope,X-ray diffractometer,nano indentation tester,microhardness tester,and tensile testing machine.The results show that the microstructures mainly consist ofα-Mg matrix,eutectic phase,and stacking faults.The addition of Nd plays a significant role in grain refinement and uniform microstructure.The tensile yield strength and microhardness increase but the compression yield strength decreases with increasing Nd addition,leading to weakening tension-compression yield asymmetry in reverse of the Mg-12Gd-2Zn-xNd-0.4Zr alloys.The highest ultimate tensile strength(194 MPa)and ultimate compression strength(397 MPa)are obtained with 1wt%Nd addition of the alloy.展开更多
Bilayer graphene quantum dots with rotational stacking faults(RSFs) having different rotational angles were studied.Using the first-principles calculation, we determined that these stacking faults could quantitatively...Bilayer graphene quantum dots with rotational stacking faults(RSFs) having different rotational angles were studied.Using the first-principles calculation, we determined that these stacking faults could quantitatively modulate the magnetism and the distribution of spin and energy levels in the electronic structures of the dots.In addition, by examining the spatial distribution of unpaired spins and Bader charge analysis, we found that the main source of magnetic moment originated from the edge atoms of the quantum dots.Our research results can potentially provide a new path for producing all-carbon nanodevices with different electrical and magnetic properties.展开更多
To develop biodegradable magnesium alloy with desirable corrosion properties,a low Gd-containing Mg-3Gd-1Zn-0.4Zr(wt%,GZ31K)alloy was prepared.The as-cast ingot was solution treated and then hot extruded.Microstructur...To develop biodegradable magnesium alloy with desirable corrosion properties,a low Gd-containing Mg-3Gd-1Zn-0.4Zr(wt%,GZ31K)alloy was prepared.The as-cast ingot was solution treated and then hot extruded.Microstructures were characterized by scanning electron microscopy(SEM).Corrosion behavior of the alloy under each condition was studied by hydrogen evolution and quasi in-situ corrosion methods.It has been found that the as-cast alloy is composed ofα-Mg,stacking faults(SFs)at the outer edge of the matrix grains,and eutectic phase along the grain boundaries.After solution treatment,the SFs disappear and precipitates rich in Zn and Zr elements form in the grain interior and boundaries.The microstructure is significantly refined after extrusion.Hydrogen evolution tests show that the as-cast alloy exhibits the best corrosion resistance,and the solution-treated alloy has the worst corrosion resistance.Corrosion rate of the alloy under each condition decreases first and then increases with prolonging immersion time.Corrosion experiments demonstrate thatα-Mg was corroded preferentially,the eutectic phase and precipitates exhibit better corrosion resistance.The as-extruded alloy demonstrates uniform corrosion due to fine and homogeneous microstructure.展开更多
The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield streng...The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing,which is related to the repulsive force between twin boundary and the dislocation.The result also shows that there is no strain-hardening at the yield point.On the contrary,the stress is raised by strain hardening in the plastic stage.In addition,we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire.The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.展开更多
■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately ...■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately with the coherent twin boundaries. Most of the steps were linked with stacking faults inside twins. Burgers vector of twinning dislocations and the mismatch strain at steps were characterized. Due to the compressive mismatch strain at steps, the high density stacking faults inside twins were formed at twin tips during twinning process. The localized strain at the steps would be related to the crack nucleation in magnesium alloys.展开更多
Partial stacking faults(PSFs) formed by incomplete mixed-mode phase transformation have been found to exhibit unfixed slip distance of closely-packed planes unlike those of the deformation-induced stacking faults(SFs)...Partial stacking faults(PSFs) formed by incomplete mixed-mode phase transformation have been found to exhibit unfixed slip distance of closely-packed planes unlike those of the deformation-induced stacking faults(SFs) with fixed distance. Though engineering PSFs can yield appealing properties, such as the enhanced damping capacity, understanding of the interaction between lattice distortion and atomic diffusion and their influences on forming PSFs is still far from being clear. Herein we performed a case study on aged Fe-Ga alloy that undergoes a mixed-mode phase transformation from body-centered cubic(BCC)to ordered face-centered cubic(FCC). The TEM investigations showed that the faulted {111}-FCC distance of the PSFs is shorter than a/6<112> of the typical {111}-<112> SFs in deformed FCC materials and the PSFs have disordered Fe and Ga arrangements. Further studies revealed that such PSFs will not be completely dissociated at FCC twin boundaries(TBs) even after long term isothermal aging. Consequently,the formation of PSFs can be ascribed to the transformation-dependent atomic ordering and lattice shear strain of the parent BCC lattice, where the diffusion-controlled glides of the PSFs-associated dislocations will accelerate atomic diffusions due to the dislocation-pipe effect along <112>-FCC direction, but may hinder the atomic diffusions across the {111}-FCC TBs due to the retarding effect. This study may add important insight into the defects process during mixed-mode phase transformation and broaden the knowledge of the interaction between concurrently-happened lattice distortion and atomic diffusion.展开更多
Near-αtitanium alloy and Ti_(2)AlNb alloy powders premixed with different proportions were prepared on the near-αtitanium alloy substrate by laser deposition technique,and the microstructure characteristics were ana...Near-αtitanium alloy and Ti_(2)AlNb alloy powders premixed with different proportions were prepared on the near-αtitanium alloy substrate by laser deposition technique,and the microstructure characteristics were analyzed and discussed.Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti_(2)AlNb above 40wt%,whereas the needle-like structure within coarse columnarβgrains exist with the proportion of Ti_(2)AlNb below 40wt%.It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures.Based on the analysis of experimental results,it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries,but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.展开更多
Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electroche...Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electrochemical activity,leading to diminished capacity and voltage performance.Herein,we introduce a Co-free LLO,Li_(1.167)Ni_(0.222)Mn_(0.611)O_(2)(Cf-L1),which features a cooperative structure of Li/Ni mixing and stacking faults.This structure regulates the crystal and electronic structures,resulting in a higher discharge capacity of 300.6 mA h g^(-1)and enhanced rate capability compared to the typical Co-free LLO,Li_(1.2)Ni_(0.2)Mn_(0.6)O_(2)(Cf-Ls).Density functional theory(DFT)indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities,while stacking faults further optimize the electronic interactions of transition metal(TM)3d and non-bonding O 2p orbitals.Moreover,stacking faults accommodate lattice strain,improving electrochemical reversibility during charge/discharge cycles,as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls.This study offers a structured approach to developing Co-free LLOs with enhanced capacity,voltage,rate capability,and cyclability,significantly impacting the advancement of the next-generation Li-ion batteries.展开更多
Line broadening in a diffraction intensity profile of powdered crystalline materials due to stacking fault has been characterized in terms of the zeroth, first, second, third, and fourth moments and the fourth cumulan...Line broadening in a diffraction intensity profile of powdered crystalline materials due to stacking fault has been characterized in terms of the zeroth, first, second, third, and fourth moments and the fourth cumulant. Calculations have been derived showing that the first moment causes a shift in the peak position of the profile while the third moment affects its shape. The intensity expression has been derived on the basis of usual Cartesian coordinates and also of polar coordinates indicated by the probability of the fault and the reciprocal lattice parameter as the two axes. The expressions for the fourth cumulant have also been so derived. Here we have used three different approaches to determine methods for calculating the fourth cumulant due to stacking faults. The three forms of the equations derived here are for different coordinate systems, but will arrive at the same answers.展开更多
Improving the strength-ductility is crucial to the development of high-performance nickel-based super-alloys fabricated via additive manufacturing(AM).In this study,Sc and Y microalloying is used to regu-late the micr...Improving the strength-ductility is crucial to the development of high-performance nickel-based super-alloys fabricated via additive manufacturing(AM).In this study,Sc and Y microalloying is used to regu-late the microstructure and improve the strength-ductility of René104 supealloy(René104ScY).The re-sults suggest the formation of high-density stacking faults(SFs),Lomer-Cottrell locks,and nano-Al_(3)(Sc,Y)phases in the René104ScY matrix.The cellular/columnar structures are refined,the number of equiax-ial grains increases,and the number of columnar grains and their aspect ratio decrease in René104ScY.The synergistic effect of multiple strengthening mechanisms,including that formed by SFs,improves the strength and ductility of René104ScY fabricated via laser powder bed fusion.The yield strength,tensile strength,and elongation of René104ScY are 1059±15 MPa,1405±10 MPa,and 28.8%±0.6%,respec-tively.This study provides a novel approach for developing high-performance nickel-based superalloys using AM.展开更多
The phase transformation of Cu-23 at.%Zn-11 at.% Al alloy from about 5℃ to 25℃ has been studied by means of the positron annihilation and transmission electron microscope. It is shown that the stacking faults in the...The phase transformation of Cu-23 at.%Zn-11 at.% Al alloy from about 5℃ to 25℃ has been studied by means of the positron annihilation and transmission electron microscope. It is shown that the stacking faults in the alloy have no remarkable effect on the trapping of positrons.展开更多
Cu,Cu-2.2%Al and Cu-4.5%Al with stacking fault energies（SFE） of 78,35 and 7 mJ/m2 respectively were processed by cold-rolling（CR） at liquid nitrogen temperature（77 K） after hot-rolling.X-ray diffraction measurem...Cu,Cu-2.2%Al and Cu-4.5%Al with stacking fault energies（SFE） of 78,35 and 7 mJ/m2 respectively were processed by cold-rolling（CR） at liquid nitrogen temperature（77 K） after hot-rolling.X-ray diffraction measurements indicate that a decrease in SFE leads to a decrease in crystallite size but increase in microstrain,dislocation and twin densities of the CR processed samples.Tensile tests at room temperature indicate that as the stacking fault energy decreases,the strength and ductility increase.The results indicate that decreasing stacking fault energy is an optimum method to improve the ductility without loss of strength.展开更多
基金supported by National Science and Technology Major Project(2025ZD0618901)National Natural Science Foundation of China(U2241245 and 52321001)+2 种基金Aeronautical Science Foundation of China(2022Z053092001)Natural Science Foundation of Shenyang(23-503-6-05)Science and Technology Major Project of Liaoning Province(2024JH1/11700028).
文摘Effects of alloying elements Ni,Co,Mn,Cr,and H on the stacking fault energy(SFE)ofγ-Fe and its microscopic mechanisms were systematically investigated.Generalized SFE calculations show that individual alloying elements Ni,Co,and H increase SFE ofγ-Fe,whereas Mn and Cr decrease SFE.The influence of alloying elements on SFE exhibits short-range characteristics.The effect of synergistic interaction of alloying elements and H on SFE was further investigated.Results show that the co-alloying of Ni/Co with H exacerbates the effect of H on the increase in SFE.In contrast,the synergistic effect of Mn/Cr with H tends to inhibit H from the increasing SFE.Finally,the electronic structure analysis elucidated the microscopic mechanism of the change in SFE.Alloying elements modulate SFE by changing the interatomic charge density at the stacking fault plane and the density of states of the stacking fault structure at the Fermi level.The present results add to the knowledge of alloying related influence on the mechanical property and hydrogen embrittlement ofγ-Fe.
基金financially supported by the National Natural Science Foundation of China(NSFC)under grant No.52371100.
文摘1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifice of plastic deformation capability[2].Lately,many strategies have been proposed to improve the comprehensive properties of materials,among which manipulating stacking fault energy(SFE)is effective[3–5].
基金supported by the Program for Hong Liu Excellent Young Scholars by Lanzhou University of Technology in 2023,the National Key Research and Development Program of China(No.2017YFA0700703)the Major Science and Technology Project of Gansu Province,China(Nos.22ZD6GA008,23ZDGC002,23ZDGA010)+1 种基金the Gansu Provincial Key Research and Development Program,China(No.20YF3GA041)the Special Fund of National Key Laboratory of Ni&Co Associated Minerals Resources Development and Comprehensive Utilization by Jinchuan Group Co.,Ltd.,China(No.GZSYS-KY-2022-012).
文摘High-density stacking faults(SFs)were introduced into a novel Ni-Co-based superalloy through warm rolling at 300-500°C,and the effects of SFs on its tensile properties at intermediate temperatures(650 and 750°C)were investigated.The results indicated that all warm rolled specimens have high-density SFs and Lomer-Cottrell locks compared with the initial specimens.Meanwhile,the simultaneous improvement of intermediate-temperature strength and ductility of alloys can be achieved by high-density SFs.In particular,the specimen rolled at 300°C exhibited a superior combination of high strength(yield and ultimate tensile strengths of(1311±18)and(1462±25)MPa respectively at 650°C,and(1180±17)and(1293±15)MPa respectively at 750°C)and high fracture elongation((26.7±2.5)%at 650°C and(10.7±1.3)%at 750°C).The high strengths and facture elongations of all warm-rolled specimens were primarily attributed to the interaction of pre-existingγ′phases,high-density SFs and Lomer-Cottrell locks with dislocations,as well as to the formation of high-density deformation nano-twins during tensile loading.
基金supported by the National Natural Science Foundation of China(No.U21A2042)the National Nature Fund Youth Fund Project of China(No.52101038)Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001).
文摘It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Phase transformation,morphology characteristics of nano twins,compressive and tensile proper-ties,and the related mechanisms have been studied.Results show that B2 phase enriched with Re tends to precipitate along theα_(2)/γinterface within lamellar colony.The stacking fault energy(SFE)ofγphase decreases from 43 mJ/m^(2) to 16 mJ/m^(2) as Re content increases from 0 at.%to 0.6 at.%,decreasing the crit-ical shear stress for twin formation.Compared to the mismatch value ofα_(2)/γinterface(0.004),which of B2/α_(2) and B2/γinterfaces increase to 0.247 and 0.149,respectively.Driven by high interfacial stress,high-density dislocations are generated at the B2/α_(2) interface,providing the dislocation slip channel for the formation of stacking faults(SFs)and nanotwins at the B2/γinterface.Therefore,the mechanism of inducting high-density nanotwins is to reduce the stacking fault energy ofγphase by Re and form highly mismatched B2/α_(2) interface.Compressive strength and the strain increase from 1723 MPa to 2398 MPa and 29%to 39%as Re content increases from 0 at.%to 0.6 at.%,respectively.Tensile strength increases from 356 MPa to 452 MPa without sacrificing plasticity.The improvement in strength and plasticity are attributed to the nano-twinning strengthening and interfacial thermal mismatch strengthening.Forming nanotwins during solidification process serve as the nucleation sites for newly formed twins during de-formation process,increasing the deformation tolerance of TiAl alloy.
基金The financial supports from the National Natural Science Foundation of China(Nos.52171107,52201203)the National Natural Science Foundation of China-Joint Fund of Iron and Steel Research(No.U1960204)the“333”Talent Project of Hebei Province,China(No.B20221001)are gratefully acknowledged.
文摘To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.
基金the Industry-University Cooperation Project in Fujian Province University(No.2022H6020)。
文摘Self-powered neutron detectors(SPNDs)play a critical role in monitoring the safety margins and overall health of reactors,directly affecting safe operation within the reactor.In this work,a novel fault identification method based on graph convolutional networks(GCN)and Stacking ensemble learning is proposed for SPNDs.The GCN is employed to extract the spatial neighborhood information of SPNDs at different positions,and residuals are obtained by nonlinear fitting of SPND signals.In order to completely extract the time-varying features from residual sequences,the Stacking fusion model,integrated with various algorithms,is developed and enables the identification of five conditions for SPNDs:normal,drift,bias,precision degradation,and complete failure.The results demonstrate that the integration of diverse base-learners in the GCN-Stacking model exhibits advantages over a single model as well as enhances the stability and reliability in fault identification.Additionally,the GCN-Stacking model maintains higher accuracy in identifying faults at different reactor power levels.
基金the National Key R&D Program of China(2017YFA0204403)National Natural Science Foundation of China(51601003,51901103)the Fundamental Research Funds for the Central Universities(30918011342).
文摘Due to the insufficient slip systems,Mg and its alloys exhibit poor ductility during plastic deformation at room temperature.To solve this problem,alloying is considered as a most effective method to improve the ductility of Mg alloys,which attracts wide attentions of industries.However,it is still a challenge to understand the ductilization mechanism,because of the complicated alloying elements and their interactions with Mg matrix.In this work,pure Mg and Mg-Y alloys were comparatively studied to investigate the effect of Y addition on microstructure evolution and mechanical properties.A huge increase of uniform elongation,from 5.3%to 20.7%,was achieved via only 3 wt%addition of yttrium.TEM results revealed that the only activated slip system in pure Mg was basalslip,led to its poor ductility at room temperature.In contrast,a large number of stacking faults and non-basal dislocations with<c>component were observed in the deformed Mg-Y alloy,which was proposed as the main reason for significant improvement of strain hardening and ductility.High resolution TEM indicated that most of the stacking faults were II and 12 intrinsic faults,which played a critical role in improving the ductility of Mg-Y alloy.Addition of Y into Mg alloy decreased the stacking fault energy,which induced high density stacking faults in the grain interior.
基金financially supported by the National Natural Science Foundation of China(No.52071175)the Natural Science Foundation of Higher Education Institutions of Jiangsu Province-Key Project,China(No.18KJA430008)+1 种基金the Key Research&Development Plan(Social Development)of Jiangsu Province,China(No.BE2020702)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX21_0923).
文摘In order to study the effects of Nd addition on microstructure and mechanical properties of Mg-Gd-Zn-Zr alloys,the microstruc-ture and mechanical properties of the as-cast Mg-12Gd-2Zn-xNd-0.4Zr(x=0,0.5wt%,and 1wt%)alloys were investigated by using optical microscope,scanning electron microscope,X-ray diffractometer,nano indentation tester,microhardness tester,and tensile testing machine.The results show that the microstructures mainly consist ofα-Mg matrix,eutectic phase,and stacking faults.The addition of Nd plays a significant role in grain refinement and uniform microstructure.The tensile yield strength and microhardness increase but the compression yield strength decreases with increasing Nd addition,leading to weakening tension-compression yield asymmetry in reverse of the Mg-12Gd-2Zn-xNd-0.4Zr alloys.The highest ultimate tensile strength(194 MPa)and ultimate compression strength(397 MPa)are obtained with 1wt%Nd addition of the alloy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11374174,51390471,51527803,and 51701143)the National Basic Research Program of China(Grant No.2015CB654902)+4 种基金the National Key Research and Development Program of China(Grant No.2016YFB0700402)the Foundation for the Author of National Excellent Doctoral Dissertation,China(Grant No.201141)the Tianjin Municipal Education Commission,Chinathe Tianjin Municipal Science and Technology Commission,Chinathe Fundamental Research Fund of Tianjin University of Technology
文摘Bilayer graphene quantum dots with rotational stacking faults(RSFs) having different rotational angles were studied.Using the first-principles calculation, we determined that these stacking faults could quantitatively modulate the magnetism and the distribution of spin and energy levels in the electronic structures of the dots.In addition, by examining the spatial distribution of unpaired spins and Bader charge analysis, we found that the main source of magnetic moment originated from the edge atoms of the quantum dots.Our research results can potentially provide a new path for producing all-carbon nanodevices with different electrical and magnetic properties.
基金This project was supported by the Natural Science Foundation of Jiangsu Province for Outstanding Youth(BK20160081)the Natural Science Foundation of Higher Education Institutions of Jiangsu Province-Key Project(18KJA430008)+2 种基金the Jiangsu Government Scholarship for Overseas Studies,the“333 Project”of Jiangsu Province(BRA2018338)the National Natural Science Foundation of China(51701093)the Outstanding Scientific and Technological Innovation Team in Colleges and Universities of Jiangsu Province.
文摘To develop biodegradable magnesium alloy with desirable corrosion properties,a low Gd-containing Mg-3Gd-1Zn-0.4Zr(wt%,GZ31K)alloy was prepared.The as-cast ingot was solution treated and then hot extruded.Microstructures were characterized by scanning electron microscopy(SEM).Corrosion behavior of the alloy under each condition was studied by hydrogen evolution and quasi in-situ corrosion methods.It has been found that the as-cast alloy is composed ofα-Mg,stacking faults(SFs)at the outer edge of the matrix grains,and eutectic phase along the grain boundaries.After solution treatment,the SFs disappear and precipitates rich in Zn and Zr elements form in the grain interior and boundaries.The microstructure is significantly refined after extrusion.Hydrogen evolution tests show that the as-cast alloy exhibits the best corrosion resistance,and the solution-treated alloy has the worst corrosion resistance.Corrosion rate of the alloy under each condition decreases first and then increases with prolonging immersion time.Corrosion experiments demonstrate thatα-Mg was corroded preferentially,the eutectic phase and precipitates exhibit better corrosion resistance.The as-extruded alloy demonstrates uniform corrosion due to fine and homogeneous microstructure.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10902083)the Program for New Scientific and Technological Star of Shaanxi Province,China (Grant No. 2012KJXX-39)
文摘The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing,which is related to the repulsive force between twin boundary and the dislocation.The result also shows that there is no strain-hardening at the yield point.On the contrary,the stress is raised by strain hardening in the plastic stage.In addition,we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire.The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.
基金supported financially by the National Natural Science Foundation of China (Nos. 11374028, U1330112 and 51621003)the National Natural Science Fund for Innovative Research Groups (No. 51621003)the Scientific Research Key Program of Beijing Municipal Commission of Education (No. KZ201310005002)
文摘■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately with the coherent twin boundaries. Most of the steps were linked with stacking faults inside twins. Burgers vector of twinning dislocations and the mismatch strain at steps were characterized. Due to the compressive mismatch strain at steps, the high density stacking faults inside twins were formed at twin tips during twinning process. The localized strain at the steps would be related to the crack nucleation in magnesium alloys.
基金This work was supported by the National Natural Science Foundation of China(Nos.51871174 and 51831006)the State Key Laboratory of Solidification Processing in NPU(No.SKLSP202003).
文摘Partial stacking faults(PSFs) formed by incomplete mixed-mode phase transformation have been found to exhibit unfixed slip distance of closely-packed planes unlike those of the deformation-induced stacking faults(SFs) with fixed distance. Though engineering PSFs can yield appealing properties, such as the enhanced damping capacity, understanding of the interaction between lattice distortion and atomic diffusion and their influences on forming PSFs is still far from being clear. Herein we performed a case study on aged Fe-Ga alloy that undergoes a mixed-mode phase transformation from body-centered cubic(BCC)to ordered face-centered cubic(FCC). The TEM investigations showed that the faulted {111}-FCC distance of the PSFs is shorter than a/6<112> of the typical {111}-<112> SFs in deformed FCC materials and the PSFs have disordered Fe and Ga arrangements. Further studies revealed that such PSFs will not be completely dissociated at FCC twin boundaries(TBs) even after long term isothermal aging. Consequently,the formation of PSFs can be ascribed to the transformation-dependent atomic ordering and lattice shear strain of the parent BCC lattice, where the diffusion-controlled glides of the PSFs-associated dislocations will accelerate atomic diffusions due to the dislocation-pipe effect along <112>-FCC direction, but may hinder the atomic diffusions across the {111}-FCC TBs due to the retarding effect. This study may add important insight into the defects process during mixed-mode phase transformation and broaden the knowledge of the interaction between concurrently-happened lattice distortion and atomic diffusion.
基金National Natural Science Foundation of China(51974259)Xi'an Municipal Bureau of Science and Technology(21ZCZZHXJS-QCY6-0008)Industry-Academic Cooperation Project of Aero Engine Corporation of China(HFZL2020CXY021)。
文摘Near-αtitanium alloy and Ti_(2)AlNb alloy powders premixed with different proportions were prepared on the near-αtitanium alloy substrate by laser deposition technique,and the microstructure characteristics were analyzed and discussed.Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti_(2)AlNb above 40wt%,whereas the needle-like structure within coarse columnarβgrains exist with the proportion of Ti_(2)AlNb below 40wt%.It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures.Based on the analysis of experimental results,it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries,but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.
基金financially supported by the National Natural Science Foundation of China(52202046,51602246,and 51801144)the Natural Science Foundation of Shanxi Provincial(2021JQ-034)。
文摘Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electrochemical activity,leading to diminished capacity and voltage performance.Herein,we introduce a Co-free LLO,Li_(1.167)Ni_(0.222)Mn_(0.611)O_(2)(Cf-L1),which features a cooperative structure of Li/Ni mixing and stacking faults.This structure regulates the crystal and electronic structures,resulting in a higher discharge capacity of 300.6 mA h g^(-1)and enhanced rate capability compared to the typical Co-free LLO,Li_(1.2)Ni_(0.2)Mn_(0.6)O_(2)(Cf-Ls).Density functional theory(DFT)indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities,while stacking faults further optimize the electronic interactions of transition metal(TM)3d and non-bonding O 2p orbitals.Moreover,stacking faults accommodate lattice strain,improving electrochemical reversibility during charge/discharge cycles,as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls.This study offers a structured approach to developing Co-free LLOs with enhanced capacity,voltage,rate capability,and cyclability,significantly impacting the advancement of the next-generation Li-ion batteries.
文摘Line broadening in a diffraction intensity profile of powdered crystalline materials due to stacking fault has been characterized in terms of the zeroth, first, second, third, and fourth moments and the fourth cumulant. Calculations have been derived showing that the first moment causes a shift in the peak position of the profile while the third moment affects its shape. The intensity expression has been derived on the basis of usual Cartesian coordinates and also of polar coordinates indicated by the probability of the fault and the reciprocal lattice parameter as the two axes. The expressions for the fourth cumulant have also been so derived. Here we have used three different approaches to determine methods for calculating the fourth cumulant due to stacking faults. The three forms of the equations derived here are for different coordinate systems, but will arrive at the same answers.
基金financially supported by the Project of Chinese Academy of Engineering(Nos.2019-XZ-11 and 2023-XY-18)the Open Fund of National Joint Engineering Research Center for Abrasion Control and Molding of Metal Materials of China(No.HKDNM201907).
文摘Improving the strength-ductility is crucial to the development of high-performance nickel-based super-alloys fabricated via additive manufacturing(AM).In this study,Sc and Y microalloying is used to regu-late the microstructure and improve the strength-ductility of René104 supealloy(René104ScY).The re-sults suggest the formation of high-density stacking faults(SFs),Lomer-Cottrell locks,and nano-Al_(3)(Sc,Y)phases in the René104ScY matrix.The cellular/columnar structures are refined,the number of equiax-ial grains increases,and the number of columnar grains and their aspect ratio decrease in René104ScY.The synergistic effect of multiple strengthening mechanisms,including that formed by SFs,improves the strength and ductility of René104ScY fabricated via laser powder bed fusion.The yield strength,tensile strength,and elongation of René104ScY are 1059±15 MPa,1405±10 MPa,and 28.8%±0.6%,respec-tively.This study provides a novel approach for developing high-performance nickel-based superalloys using AM.
文摘The phase transformation of Cu-23 at.%Zn-11 at.% Al alloy from about 5℃ to 25℃ has been studied by means of the positron annihilation and transmission electron microscope. It is shown that the stacking faults in the alloy have no remarkable effect on the trapping of positrons.
基金Project (50874056) supported by the National Natural Science Foundation of China
文摘Cu,Cu-2.2%Al and Cu-4.5%Al with stacking fault energies（SFE） of 78,35 and 7 mJ/m2 respectively were processed by cold-rolling（CR） at liquid nitrogen temperature（77 K） after hot-rolling.X-ray diffraction measurements indicate that a decrease in SFE leads to a decrease in crystallite size but increase in microstrain,dislocation and twin densities of the CR processed samples.Tensile tests at room temperature indicate that as the stacking fault energy decreases,the strength and ductility increase.The results indicate that decreasing stacking fault energy is an optimum method to improve the ductility without loss of strength.
