In order to construct quasi-continuously networked reinforcement in titanium(Ti)matrix composites,in this study,Ti-6 Al-4 V spherical powders were uniformly coated with a graphene nanosheet(GNS)layer by high energy ba...In order to construct quasi-continuously networked reinforcement in titanium(Ti)matrix composites,in this study,Ti-6 Al-4 V spherical powders were uniformly coated with a graphene nanosheet(GNS)layer by high energy ball milling and then consolidated by spark plasma sintering.Results showed that the GNS layer on the powder surface inhibited continuous metallurgy bonding between powders during sintering,which led to the formation of quasi-networked hybrid reinforcement structure consisting of insitu Ti C and remained GNSs.The networked GNSs/Ti64 composite possessed noticeably higher tensile strength but similar ductility to the Ti64 alloy,leading to both better tensile strength and ductility than the GNSs/Ti composite with randomly dispersed GNSs and Ti C.The formation mechanism and the fracture mechanism of the networked hybrid reinforcement were discussed.The results provided a method to fabricate Ti matrix composites with high strength and good ductility.展开更多
The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been...The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been produced easily under condition that selecting pipes well distributed on the wall thickness ,proper preheating temperature and appropriate additive.展开更多
At 45 MeV/u an experiment on fragmentation of projectile(<sup>20</sup>Ne)on <sup>165</sup>Ho was performed.An average reduced width σ<sub>0</sub> of 84.3±6.6 MeV/c was obtaine...At 45 MeV/u an experiment on fragmentation of projectile(<sup>20</sup>Ne)on <sup>165</sup>Ho was performed.An average reduced width σ<sub>0</sub> of 84.3±6.6 MeV/c was obtained by separating the break=up of all com-plex fragments of <sup>20</sup>Ne from the evaporation part of compound nucleus in momentum spectra.展开更多
The role of melt cooling rate on the interface morphology and dislocation configuration between 18R long-period stacking ordered(LPSO)structure and Mg matrix in Mg_(97)Zn_(1)Y_(2)(at.%)alloys was investigated by atomi...The role of melt cooling rate on the interface morphology and dislocation configuration between 18R long-period stacking ordered(LPSO)structure and Mg matrix in Mg_(97)Zn_(1)Y_(2)(at.%)alloys was investigated by atomic-scale HAADF-STEM imaging.The 18R/Mg interface is step-like both in the near-equilibrium alloy and non-equilibrium alloy.Lower cooling rate makes the step size more regular and larger.Only 54R structure can be observed at the interface in the near-equilibrium alloy,and the dislocations are highly ordered.54R and 54R′structure sandwiched by b1 and b2+b3 dislocation arrays,and new dislocation configuration can be detected at the interface in the non-equilibrium alloy,but the dislocations are less ordered.18R/Mg interface containing 54R or 54R′in equilibrium width,parallel to the(010)plane,should be most stable based on elastic calculation.The segregation of solute atoms and its strong interaction with dislocations dominate the LPSO/Mg interface via diffusion-displacive transformation.展开更多
The principle of production of polymer mineral composite was analyzed. Property parameters and the procedure for producing PMC components were also given. Damping property and principle of vibration absorption of poly...The principle of production of polymer mineral composite was analyzed. Property parameters and the procedure for producing PMC components were also given. Damping property and principle of vibration absorption of polymer mineral composite were also investigated. Reduced experiment was conducted for two jigs which are similar in structure only different in material that one made of PMC the other made of casting iron to test their dynamic characteristic.展开更多
BAS (BaAl 2Si 2O 8) glass ceramic was prepared by a sol gel process and the SiC W/BAS composites were fabricated by hot pressing. The transformation from hexacelsian to celsian, the microstructure and mechanical prope...BAS (BaAl 2Si 2O 8) glass ceramic was prepared by a sol gel process and the SiC W/BAS composites were fabricated by hot pressing. The transformation from hexacelsian to celsian, the microstructure and mechanical properties of the composites was investigated. The results show that the transformation promoted by adding celsian seeds is retarded in the composite by the presence of SiC whisker. SiC whisker has a good effect of improving the mechanical properties of BAS glass ceramic matrix. The toughening mechanisms are crack deflection and whisker fracture. The strengthening mechanism is loading transition. The amorphous phase at SiC W/BAS matrix interface damages the fracture toughness and high temperature strength of the composites.展开更多
Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper, the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness ...Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper, the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness parameters are investigated.Atheoretical model is proposed to study wetting transitions.The results of theoretical analysis are compared with those of experimentindicating that the proposed model can effectively predict the wetting transition.Furthermore, a numerical simulationbased on the meso scale Lattice Boltzmann Method （LBM） is performed to study dynamic contact angles, contact lines, andlocal velocity fields for the case that a droplet displays on the micro structured surface.A spherical water droplet with r= 15 μmfalls down to a biomimetic square-post patterned surface under the force of gravity with an initial velocity of 0.01 m·sand aninitial vertical distance of 20 μm from droplet centre to the top of pots.In spite of a higher initial velocity, the droplet can stillstay in a Cassie state; moreover, it reaches an equilibrium state at t≈17.5 ms, when contact angle is 153.16° which is slightlylower than the prediction of Cassie-Baxter’s equation which gives θ=154.40°.展开更多
The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ri...The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou.The new mass excess value allowed us to determine the excitation energies of the two low-lying 1+states in ^(22)Al with significantly reduced uncertainties of 51 keV.When compared to the analogue states in its mirror nucleus ^(22)F,the mirror energy differences of the two 1^(+)states in the ^(22)Al-^(22)F mirror pair are determined to be−625(51)keV and−330(51)keV.The excitation energies and mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory.The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of theπs_(1/2) orbital.展开更多
Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization pr...Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization process,which has not been fully understood in the typical Mg-RE based alloy.In this work,it is claimed for the first time that the minor Ce addition(∼0.3 wt%)into Mg matrix significantly pro-motes the pyramidal<c+a>and non-basal<a>dislocations at the early stage of extrusion,which con-sequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type<c+a>dislocations.At this stage,fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of<c+a>dislocations.At the later stage,the sub-grains continuously transform into dynamic recrystallized(DRXed)grains that have10¯10Taylor axis and also strong fiber texture,indicating substantial activation of pyramidal II-type<c+a>dislocation.The low mobility of<c+a>dislocations,accompanied with the solute drag from grain boundary(GB)segregation and pinning from nano-phases,cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains,∼0.51μm.The resultant texture hardening and grain refinement hardening effects,originated from bimodal microstructure,result in a yield strength of∼352 MPa,which is exceptional in Mg-Ce dilute alloy.This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium,and can also shed light on designing the other high-performance Mg alloys.展开更多
The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grain...The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.展开更多
A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating ...A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating with the evolution of mechanical properties is systematically characterized during the subsequent aging treatment at 200°C.The extruded alloy presents an outstanding strength with tensile yield strength of 466 MPa and ultimate tensile strength of 500 MPa at peak aging condition,while the elongation drops from 9.2%in extrusion state to 3.1%.It is found there obviously exist a rapidly decreasing range of ductility at the early stage of aging.Just during this time,the nano precipitates form preferentially at lamellar dislocation boundaries(LDBs)within the elongated grains,but there is no dense and uniform precipitation in the matrix.The results suggest that the low elongation in the aged Mg^(-1)5Gd alloy is mainly attributed to the nano precipitates prior formed at the LDBs with a high density in the elongated grains.The related mechanism has been clarified.展开更多
Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical co...Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades.In this work,thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples.We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field,and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains.When the unfavorably oriented grain is low misoriented,unfavorably oriented grain dominates grain selection,and the competitive grain growth performs as solute field domination.However,with the increase of unfavorably oriented grain’s misorientation,the grain selection converts into favorably oriented grain domination,and the competitive grain growth changes to thermal condition domination.To explain these abnormal transformation phenomena,we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation(θ_(cm)).According to dynamic equation of dendrite growth,we calculate the critical misorientationθ;to prove this model.The theoretical calculation results agree well with the experimental results.展开更多
Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at ...Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at 6.89 MeV is observed for the first time.The inelastic scattering angular distributions of these two states are well reproduced by the distorted-wave Born approximation(DWBA)calculation with an l=1 excitation.In addition,the spinparities of the unbound states are discussed and tentatively assigned based on shell model calculations using the modified YSOX interaction.展开更多
Utilizing ultrafine iron ore concentrate for pellet production can expand domestic iron ore resources in China and promote the utilization of low-grade ores.However,a challenge arises with the low decrepitation temper...Utilizing ultrafine iron ore concentrate for pellet production can expand domestic iron ore resources in China and promote the utilization of low-grade ores.However,a challenge arises with the low decrepitation temperature and reducibility in the preparation process of ultrafine iron ore concentrate pellets.To address the challenge,a novel approach was proposed,which incorporated straw powder as an additive to enhance pellet porosity,thereby improving the decrepitation temper-ature and reducibility of ultrafine iron ore concentrate pellets.The effect of varying proportions of straw powder(0.0-2.0%)on the characteristics of ultrafine iron ore concentrate pellets was examined.Results indicate that at a 2.0%straw powder ratio,pellet decrepitation temperature notably rises from 380 to 540℃,while the reducibility index escalates from 25.7%to 48.1%.Nevertheless,the addition of straw powder results in diminished drop strength,compressive strength of green pellets,and cold crushing strength of fired pellets.In addition,enhanced pellet reducibility leads to exacerbated reduction swelling index and reduction degradation index.Despite these effects,all parameters remain within an acceptable range.展开更多
A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitut...A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 K.The Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.展开更多
Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–...Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^（-1）. The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves（dynamic recrystallization and dynamic recovery） were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^（-1） and deformation temperature of 1200℃ as compared to other deformation conditions.展开更多
基金financially supported by the Key Research and Development Plan of Shaanxi Province(No.2020KW-034)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX2021058)。
文摘In order to construct quasi-continuously networked reinforcement in titanium(Ti)matrix composites,in this study,Ti-6 Al-4 V spherical powders were uniformly coated with a graphene nanosheet(GNS)layer by high energy ball milling and then consolidated by spark plasma sintering.Results showed that the GNS layer on the powder surface inhibited continuous metallurgy bonding between powders during sintering,which led to the formation of quasi-networked hybrid reinforcement structure consisting of insitu Ti C and remained GNSs.The networked GNSs/Ti64 composite possessed noticeably higher tensile strength but similar ductility to the Ti64 alloy,leading to both better tensile strength and ductility than the GNSs/Ti composite with randomly dispersed GNSs and Ti C.The formation mechanism and the fracture mechanism of the networked hybrid reinforcement were discussed.The results provided a method to fabricate Ti matrix composites with high strength and good ductility.
文摘The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been produced easily under condition that selecting pipes well distributed on the wall thickness ,proper preheating temperature and appropriate additive.
基金①The project supported by the U.S.Department of Energy.the Robert A.Welch Foundation theNational Natural Science Foundation of China
文摘At 45 MeV/u an experiment on fragmentation of projectile(<sup>20</sup>Ne)on <sup>165</sup>Ho was performed.An average reduced width σ<sub>0</sub> of 84.3±6.6 MeV/c was obtained by separating the break=up of all com-plex fragments of <sup>20</sup>Ne from the evaporation part of compound nucleus in momentum spectra.
基金This work is supported by the National Natural Science Foundation of China(grant number 51801214 and 51871222)Guangxi Science and Technology Base and Talents Special Project(Guike AD20297034)+2 种基金Liaoning Provincial Natural Science Foundation(2019-MS-335)Research Start-up Funding from Guangxi University of Science and Technology(No.03200150)Natural Science Foundation of Hebei Province of China(grant number E2020208083).
文摘The role of melt cooling rate on the interface morphology and dislocation configuration between 18R long-period stacking ordered(LPSO)structure and Mg matrix in Mg_(97)Zn_(1)Y_(2)(at.%)alloys was investigated by atomic-scale HAADF-STEM imaging.The 18R/Mg interface is step-like both in the near-equilibrium alloy and non-equilibrium alloy.Lower cooling rate makes the step size more regular and larger.Only 54R structure can be observed at the interface in the near-equilibrium alloy,and the dislocations are highly ordered.54R and 54R′structure sandwiched by b1 and b2+b3 dislocation arrays,and new dislocation configuration can be detected at the interface in the non-equilibrium alloy,but the dislocations are less ordered.18R/Mg interface containing 54R or 54R′in equilibrium width,parallel to the(010)plane,should be most stable based on elastic calculation.The segregation of solute atoms and its strong interaction with dislocations dominate the LPSO/Mg interface via diffusion-displacive transformation.
文摘The principle of production of polymer mineral composite was analyzed. Property parameters and the procedure for producing PMC components were also given. Damping property and principle of vibration absorption of polymer mineral composite were also investigated. Reduced experiment was conducted for two jigs which are similar in structure only different in material that one made of PMC the other made of casting iron to test their dynamic characteristic.
文摘BAS (BaAl 2Si 2O 8) glass ceramic was prepared by a sol gel process and the SiC W/BAS composites were fabricated by hot pressing. The transformation from hexacelsian to celsian, the microstructure and mechanical properties of the composites was investigated. The results show that the transformation promoted by adding celsian seeds is retarded in the composite by the presence of SiC whisker. SiC whisker has a good effect of improving the mechanical properties of BAS glass ceramic matrix. The toughening mechanisms are crack deflection and whisker fracture. The strengthening mechanism is loading transition. The amorphous phase at SiC W/BAS matrix interface damages the fracture toughness and high temperature strength of the composites.
基金supported by the Royal Society(UK)-NSFC(China)joint project,2009-2011by China Natural Science Foundation major International collaborative project 2010-2013 under grant No.50920105504
文摘Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper, the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness parameters are investigated.Atheoretical model is proposed to study wetting transitions.The results of theoretical analysis are compared with those of experimentindicating that the proposed model can effectively predict the wetting transition.Furthermore, a numerical simulationbased on the meso scale Lattice Boltzmann Method （LBM） is performed to study dynamic contact angles, contact lines, andlocal velocity fields for the case that a droplet displays on the micro structured surface.A spherical water droplet with r= 15 μmfalls down to a biomimetic square-post patterned surface under the force of gravity with an initial velocity of 0.01 m·sand aninitial vertical distance of 20 μm from droplet centre to the top of pots.In spite of a higher initial velocity, the droplet can stillstay in a Cassie state; moreover, it reaches an equilibrium state at t≈17.5 ms, when contact angle is 153.16° which is slightlylower than the prediction of Cassie-Baxter’s equation which gives θ=154.40°.
基金Supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000)the CAS Project for Young Scientists in Basic Research (YSBR-002)+4 种基金the National Nature Science Foundation of China (12135017,12121005,11975280,12105333,12205340,12322507,12305126,12305151)the Gansu Natural Science Foundation (22JR5RA123,23JRRA614)the National Key R&D Program of China (2021YFA1601500)Support from the Youth Innovation Promotion Association of Chinese Academy of Sciences (2021419,2022423)support from Young Scholar of Regional Development,CAS ([2023]15).
文摘The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou.The new mass excess value allowed us to determine the excitation energies of the two low-lying 1+states in ^(22)Al with significantly reduced uncertainties of 51 keV.When compared to the analogue states in its mirror nucleus ^(22)F,the mirror energy differences of the two 1^(+)states in the ^(22)Al-^(22)F mirror pair are determined to be−625(51)keV and−330(51)keV.The excitation energies and mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory.The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of theπs_(1/2) orbital.
基金supported by National Key Research and De-velopment Program of China(No.2021YFB3701002)National Nat-ural Science Foundation of China(No.U2167213,51971053)+1 种基金and funded by the Project of Promoting Talents in Liaoning province(No.XLYC1808038).H.C.Pan acknowledges the financial assistance from Young Elite Scientists Sponsorship Program by CAST(2019-2021QNRC001,2019-2021QNRC002,2019-2021QNRC003)the fund from the Fundamental Research Funds for the Central Univer-sities(N2202020).
文摘Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization process,which has not been fully understood in the typical Mg-RE based alloy.In this work,it is claimed for the first time that the minor Ce addition(∼0.3 wt%)into Mg matrix significantly pro-motes the pyramidal<c+a>and non-basal<a>dislocations at the early stage of extrusion,which con-sequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type<c+a>dislocations.At this stage,fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of<c+a>dislocations.At the later stage,the sub-grains continuously transform into dynamic recrystallized(DRXed)grains that have10¯10Taylor axis and also strong fiber texture,indicating substantial activation of pyramidal II-type<c+a>dislocation.The low mobility of<c+a>dislocations,accompanied with the solute drag from grain boundary(GB)segregation and pinning from nano-phases,cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains,∼0.51μm.The resultant texture hardening and grain refinement hardening effects,originated from bimodal microstructure,result in a yield strength of∼352 MPa,which is exceptional in Mg-Ce dilute alloy.This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium,and can also shed light on designing the other high-performance Mg alloys.
文摘The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.
基金supported by National Natural Science Foundation of China(Grant Nos.52171121,51971151,52201131,52201132,52171055 and 52071220)Liao Ning Xingliao Program(XLYC1907083)+1 种基金Natural Science Foundation of Liaoning Province of China(2022-NLTS-18-01)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education(HEU10202205).
文摘A bimodal-structured Mg^(-1)5Gd binary alloy with 45%volume fraction of elongated grains and 55%of dynamically recrystallized(DRXed)grains is fabricated by the extrusion process.The precipitating behavior correlating with the evolution of mechanical properties is systematically characterized during the subsequent aging treatment at 200°C.The extruded alloy presents an outstanding strength with tensile yield strength of 466 MPa and ultimate tensile strength of 500 MPa at peak aging condition,while the elongation drops from 9.2%in extrusion state to 3.1%.It is found there obviously exist a rapidly decreasing range of ductility at the early stage of aging.Just during this time,the nano precipitates form preferentially at lamellar dislocation boundaries(LDBs)within the elongated grains,but there is no dense and uniform precipitation in the matrix.The results suggest that the low elongation in the aged Mg^(-1)5Gd alloy is mainly attributed to the nano precipitates prior formed at the LDBs with a high density in the elongated grains.The related mechanism has been clarified.
基金financially supported by the Shandong Provincial Natural Science Foundation(No.ZR2020ME110)the National Natural Science Foundation of China(Nos.51331005,U1508213,51771190 and 51601102)+2 种基金the Fund of the State Key Laboratory of Solidification Processing in NWPU(Nos.SKLSP201847 and SKLSP201834)the Young Doctors Cooperation Project in Qilu University of Technology(No.2018BSHZ003)the Key Research and Development Program of Ningxia(No.2019BDE03016)。
文摘Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades.In this work,thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples.We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field,and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains.When the unfavorably oriented grain is low misoriented,unfavorably oriented grain dominates grain selection,and the competitive grain growth performs as solute field domination.However,with the increase of unfavorably oriented grain’s misorientation,the grain selection converts into favorably oriented grain domination,and the competitive grain growth changes to thermal condition domination.To explain these abnormal transformation phenomena,we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation(θ_(cm)).According to dynamic equation of dendrite growth,we calculate the critical misorientationθ;to prove this model.The theoretical calculation results agree well with the experimental results.
基金Supported by the National Key R&D Program of China(2018YFA0404403)the National Natural Science Foundation of China(11775004,U1867214,11875074,11961141003)+1 种基金the funding from the State Key Laboratory of Nuclear Physics and Technology,Peking University(NPT2021ZZ01)the funding from Heavy Ion Research Facility in Lanzhou(HIR2021PY002)。
文摘Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at 6.89 MeV is observed for the first time.The inelastic scattering angular distributions of these two states are well reproduced by the distorted-wave Born approximation(DWBA)calculation with an l=1 excitation.In addition,the spinparities of the unbound states are discussed and tentatively assigned based on shell model calculations using the modified YSOX interaction.
基金support from the National Natural Science Foundation of China(No.U1860113)for providing funding to complete the experiments.
文摘Utilizing ultrafine iron ore concentrate for pellet production can expand domestic iron ore resources in China and promote the utilization of low-grade ores.However,a challenge arises with the low decrepitation temperature and reducibility in the preparation process of ultrafine iron ore concentrate pellets.To address the challenge,a novel approach was proposed,which incorporated straw powder as an additive to enhance pellet porosity,thereby improving the decrepitation temper-ature and reducibility of ultrafine iron ore concentrate pellets.The effect of varying proportions of straw powder(0.0-2.0%)on the characteristics of ultrafine iron ore concentrate pellets was examined.Results indicate that at a 2.0%straw powder ratio,pellet decrepitation temperature notably rises from 380 to 540℃,while the reducibility index escalates from 25.7%to 48.1%.Nevertheless,the addition of straw powder results in diminished drop strength,compressive strength of green pellets,and cold crushing strength of fired pellets.In addition,enhanced pellet reducibility leads to exacerbated reduction swelling index and reduction degradation index.Despite these effects,all parameters remain within an acceptable range.
基金supported by the National Natural Science Foundation of China(Grant Nos.51227001 and 51471108)the SJTU-UNSW Cooperative Research Fund(16X120030005)
文摘A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 K.The Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.
基金financially supported by the National Program on Key Basic Research Project (Grant No. 2011CB606306-2)the National Natural Science Foundation of China (Grant No. 51775102)
文摘Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^（-1）. The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves（dynamic recrystallization and dynamic recovery） were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^（-1） and deformation temperature of 1200℃ as compared to other deformation conditions.
