Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase tra...Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase transition have rarely been reported yet.Herein,we discovered ferroelasticity in a pair of organic enantiomers,(1S and/or 1R)-2,10-camphorsultam(S-and R-CPS),which undergoes a high-T_(c)plastic phase transition.Both large entropies change of∼45 J mol^(-1)K^(-1)and evidently ductile deformation process confirm the plastic phase feature.Strip-like ferroelastic domain patterns and bidirectional domain movements have been observed via polarized light microscopy and nanoindentation technique,respectively.This work highlights the discovery of organic ferroelastic combining the features of enantiomers and plastic phase transition,which contributes insights into exploration of organic multifunctional materials.展开更多
1 Scope This standard specifies the definition, classification, technical requirements, test methods, inspection rules, packing, marking, transportation and quality certificate of corundum block containing plastic ph...1 Scope This standard specifies the definition, classification, technical requirements, test methods, inspection rules, packing, marking, transportation and quality certificate of corundum block containing plastic phase.展开更多
The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The r...The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The results are compared with those using differential scheme. It is shown that the material properties derived from the present model normally are larger than those obtained by differential scheme for foam plastics with identical porosity. The differences in shear moduli and Young's moduli obtained by the two methods are small but they are larger for bulk moduli of incompressible matrix and Poisson's ratios. The Young's moduli of high density foam plastics derived by the present model agree better with experimental ones.展开更多
High temperature rupture specimens with different rapture plasticity are investigated. The rupture fracture failure of Inconel 783 superalloy is researched by analyzing the fracture surface and microstructure of the r...High temperature rupture specimens with different rapture plasticity are investigated. The rupture fracture failure of Inconel 783 superalloy is researched by analyzing the fracture surface and microstructure of the rupture specimens. The intergranular β phase precipitated sufficiently with favorable morphology can efficiently strengthen grain boundaries that can achieve a full plastic deformation of grains. Additionally, the intergranular β phase can effectively restrain the occurrence and expansion of intergranular cracks during the rupture test. The intergranular β phase insufficiently precipitated can weaken the intergranular cohesion and lead to the occurrence and expansion of cracks; thus, the grains cannot be fully deformed before breaking. Therefore, the β phase precipitated in the grain boundaries can significantly increase the rupture plasticity of Inconel 783 superalloy.展开更多
Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase ...Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase transformations on the plastic behaviour of a low-alloy steel. It is now well known that the plastic strain rate can then be decomposed as the sum of two terms. The first one corresponds to classical plasticity while the second one is due to the evolution of the transformation and is usually referred to as corresponding to transformation induced plasticity. A theoretical approach of the problem has been achieved ([1][2][3]] and a macroscopic model has been proposed in the case of ideal-plastic phases. The theoretical approach has been assessed and completed using micromechanical numerical simulations but these were based on rather coarse 3D meshes due to limited computer capabilities in the 80’s. This paper presents new finite element micromechanical calculations using refined meshes to analyse the classical plastic behaviour and transformation induced plasticity. The results of the computations are discussed and compared with the calculations initially performed. Finally improvements of the macroscopic model are proposed.展开更多
For the first time, for different organic and inorganic compounds possessing the plastic crystalline phase, a new semiempirical equation describing dependence of their fusion enthalpies on such physico-chemical quanti...For the first time, for different organic and inorganic compounds possessing the plastic crystalline phase, a new semiempirical equation describing dependence of their fusion enthalpies on such physico-chemical quantities as normal melting temperature, surface tension, molar volume and critical molar volume is received on the base of the principle of corresponding states and the energy equipartition theorem. Moreover, the proposed equation allows one to take into account the particularities of one-particle molecular rotation in the plastic crystalline phase.展开更多
Coupled relations among temperature, phase transformation and stress have beendiscussed here in the present paper. Thermo-elasto-plastic constitutive equationsincluding creep and iterative finite element formulation d...Coupled relations among temperature, phase transformation and stress have beendiscussed here in the present paper. Thermo-elasto-plastic constitutive equationsincluding creep and iterative finite element formulation during continuous casting withphase change have also been presented.展开更多
Phase transitions widely exist in nature and occur when some control parameters are changed. In neural systems, their macroscopic states are represented by the activity states of neuron populations, and phase transiti...Phase transitions widely exist in nature and occur when some control parameters are changed. In neural systems, their macroscopic states are represented by the activity states of neuron populations, and phase transitions between different activity states are closely related to corresponding functions in the brain. In particular, phase transitions to some rhythmic synchronous firing states play significant roles on diverse brain functions and disfunctions, such as encoding rhythmical external stimuli, epileptic seizure, etc. However, in previous studies, phase transitions in neuronal networks are almost driven by network parameters （e.g., external stimuli）, and there has been no investigation about the transitions between typical activity states of neuronal networks in a self-organized way by applying plastic connection weights. In this paper, we discuss phase transitions in electrically coupled and lattice-based small-world neuronal networks （LBSW networks） under spike-timing-dependent plasticity （STDP）. By applying STDP on all electrical synapses, various known and novel phase transitions could emerge in LBSW networks, particularly, the phenomenon of self-organized phase transitions （SOPTs）： repeated transitions between synchronous and asynchronous firing states. We further explore the mechanics generating SOPTs on the basis of synaptic weight dynamics.展开更多
Based on the assumption that a representative element of apearlitic steel is an aggregate of numerous spherical pearliticcolonies with randomly distributed orientations, and that each colonyis com- posed of many paral...Based on the assumption that a representative element of apearlitic steel is an aggregate of numerous spherical pearliticcolonies with randomly distributed orientations, and that each colonyis com- posed of many parallel fine lamellas of ferrite andcementite, a description for the dual-phase pearlitic steel isobtained by making use of a microstructure-based constitutiveequation for a single dual-phase pearlitic colony and the Hill'sself-consistent scheme. The elastoplastic response of dual-phasepearlitic steel BS11 subjected to asymmetrically cyclic loading isanalyzed, and a comparison with the experimental results showssatisfacto- ry agreement. The non-proportional cyclic plasticity ofBS11 is also analyzed, in which stress develops along a semi-circlein a biaxial tension/compression and shear stress plane, as istypically experienced by the sur- face elements in rolling andsliding contact.展开更多
The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electro...The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.展开更多
The influence of deformation temperature,strain rate and alloying elements such as chromium,nickel,copper,on corrosion resistance of a 304 stainless steel after plastic deformation was investigated.The techniques empl...The influence of deformation temperature,strain rate and alloying elements such as chromium,nickel,copper,on corrosion resistance of a 304 stainless steel after plastic deformation was investigated.The techniques employed were tensile test at room and elevated temperature,deep drawing tests at various strain rates,X-ray diffraction test and potentiodynamic and cyclic polarization,metallography by optical and scanning electron microscopy.Results showed that chromium,nickel and copper had a significant effect on corrosion resistance of steel after plastic deformation.It was observed that corrosion resistance after plastic deformation was a function of deformation temperature and alloying elements.展开更多
Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many coun...Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.展开更多
The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temper...The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temperature.The microstructure and tensile properties of composites were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and tensile testing machine at room temperature.The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly.The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5 MPa,respectively,when the amount of I-phase particles added is10 %.Meanwhile,the elongation of the composites decreases sharply.展开更多
With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys(HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation b...With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys(HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation behavior in these solid-solution alloys. It is shown that the maximum shear stress (max)required for dislocation nucleation is determined to be 1/16-1/12 and 1/18-1/14 of shear modulus for the TiZrNbTa and TiZrNbTaMo HEAs, respectively, which is nearly comparative to the theoretical shear stress of these alloys. The activation volumes of dislocation nucleation the TiZrNbTa and TiZrNbTaMo HEAs are determined to be 1.2 b^3 for and 1.3 b^3, respectively, which is substantially irrespective of alloying with Mo. Furthermore, activation volumes of these two HEAs are on the order of cubic burger’s vector and only one-third of the value for TiZrHfNb HEA, suggesting that a heterogeneous nucleation of dislocation took place in a way of direct atom-vacancy exchange, rather than of the cooperative motion of several atoms. These findings reveal the unique feature in deformation of BCC solid-solution complex alloys.展开更多
To determine the time-independent constitutive modeling for porous and multi- phase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated ...To determine the time-independent constitutive modeling for porous and multi- phase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated as a mixture of grain interior and grain bound- ary, and pores were taken as a single phase, then Budiansky＇s self-consistent method was used to calculate the Young＇s modulus of porous, possible multi-phase, nanocrystalline materials, the prediction being in good agreement with the results in the literature. Further, the established method is extended to simulate the constitutive relations of porous and possible multi-phase nanocrystalline materials with small plastic deformation in conjunction with the secant-moduli approach and iso-strain assumption. Comparisons between the experimental grain size and porosity dependent mechanical data and the corresponding predictions using the established model show that it appears to be capable of describing the time-independent mechanical behaviors for porous and multi-phase nanocrystalline materials in a small plastic strain range. Further discussion on the modification factor, the advantages and limitations of the model developed were present.展开更多
Optical, cathodoluminescence and transmission electron microscope (TEM)analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclasticcoarse-grained marbles from two fault zones, an...Optical, cathodoluminescence and transmission electron microscope (TEM)analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclasticcoarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks showsimilar microstructural characteristics and give clues to similar processes of rock deformation.They are characterized by the structural contrast between macroscopic cataclastic (brittle) andmicroscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e.deformation twins, kink bands and microfractures) are well preserved in the deformed grains inclasts or in primary rocks. The matrix materials are of extremely fine grains with diffusivefeatures. Dislocation microstructures for co-existing brittle deformation and crystalline plasticitywere revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformedclasts, while dislocation walls form in the transitions to the fine-grained matrix materials andfree dislocations, dislocation loops and dislocation dipoles are observed both in the deformedclasts and in the fine-grained matrix materials. Dynamic recrystallization grains from subgrainrotation recrystallization and subsequent grain boundary migration constitute the major parts of thematrix materials. Statistical measurements of densities of free dislocations, grain sizes ofsubgrains and dynamically recrystallized grains suggest an unsteady state of the rock deformation.Microstructural and cathodoluminescence analyses prove that fluid activity is one of the major partsof faulting processes. Low-temperature plasticity, and thereby induced co-existence of macroscopicbrittle and microscopic ductile microstructures are attributed to hydrolytic weakening due to theinvolvement of fluid phases in deformation and subsequent variation of rock rheology. Duringhydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, andincrease the rate of recovery of strain-hardened rocks, which accommodates fracturing.展开更多
基金supported by the National Natural Science Foundation of China(No.22271131)the Department of Science and Technology in Jiangxi Province(No.20225BCJ23029).
文摘Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase transition have rarely been reported yet.Herein,we discovered ferroelasticity in a pair of organic enantiomers,(1S and/or 1R)-2,10-camphorsultam(S-and R-CPS),which undergoes a high-T_(c)plastic phase transition.Both large entropies change of∼45 J mol^(-1)K^(-1)and evidently ductile deformation process confirm the plastic phase feature.Strip-like ferroelastic domain patterns and bidirectional domain movements have been observed via polarized light microscopy and nanoindentation technique,respectively.This work highlights the discovery of organic ferroelastic combining the features of enantiomers and plastic phase transition,which contributes insights into exploration of organic multifunctional materials.
文摘1 Scope This standard specifies the definition, classification, technical requirements, test methods, inspection rules, packing, marking, transportation and quality certificate of corundum block containing plastic phase.
基金Supported by the National Natural Science Foundation of China and Laboratory for Nonlinear Mechanics of Continuous Media,Institute of Mechanics,Chinese Academy of Sciences.
文摘The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The results are compared with those using differential scheme. It is shown that the material properties derived from the present model normally are larger than those obtained by differential scheme for foam plastics with identical porosity. The differences in shear moduli and Young's moduli obtained by the two methods are small but they are larger for bulk moduli of incompressible matrix and Poisson's ratios. The Young's moduli of high density foam plastics derived by the present model agree better with experimental ones.
文摘High temperature rupture specimens with different rapture plasticity are investigated. The rupture fracture failure of Inconel 783 superalloy is researched by analyzing the fracture surface and microstructure of the rupture specimens. The intergranular β phase precipitated sufficiently with favorable morphology can efficiently strengthen grain boundaries that can achieve a full plastic deformation of grains. Additionally, the intergranular β phase can effectively restrain the occurrence and expansion of intergranular cracks during the rupture test. The intergranular β phase insufficiently precipitated can weaken the intergranular cohesion and lead to the occurrence and expansion of cracks; thus, the grains cannot be fully deformed before breaking. Therefore, the β phase precipitated in the grain boundaries can significantly increase the rupture plasticity of Inconel 783 superalloy.
文摘Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase transformations on the plastic behaviour of a low-alloy steel. It is now well known that the plastic strain rate can then be decomposed as the sum of two terms. The first one corresponds to classical plasticity while the second one is due to the evolution of the transformation and is usually referred to as corresponding to transformation induced plasticity. A theoretical approach of the problem has been achieved ([1][2][3]] and a macroscopic model has been proposed in the case of ideal-plastic phases. The theoretical approach has been assessed and completed using micromechanical numerical simulations but these were based on rather coarse 3D meshes due to limited computer capabilities in the 80’s. This paper presents new finite element micromechanical calculations using refined meshes to analyse the classical plastic behaviour and transformation induced plasticity. The results of the computations are discussed and compared with the calculations initially performed. Finally improvements of the macroscopic model are proposed.
文摘For the first time, for different organic and inorganic compounds possessing the plastic crystalline phase, a new semiempirical equation describing dependence of their fusion enthalpies on such physico-chemical quantities as normal melting temperature, surface tension, molar volume and critical molar volume is received on the base of the principle of corresponding states and the energy equipartition theorem. Moreover, the proposed equation allows one to take into account the particularities of one-particle molecular rotation in the plastic crystalline phase.
文摘Coupled relations among temperature, phase transformation and stress have beendiscussed here in the present paper. Thermo-elasto-plastic constitutive equationsincluding creep and iterative finite element formulation during continuous casting withphase change have also been presented.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11135001 and 11174034)
文摘Phase transitions widely exist in nature and occur when some control parameters are changed. In neural systems, their macroscopic states are represented by the activity states of neuron populations, and phase transitions between different activity states are closely related to corresponding functions in the brain. In particular, phase transitions to some rhythmic synchronous firing states play significant roles on diverse brain functions and disfunctions, such as encoding rhythmical external stimuli, epileptic seizure, etc. However, in previous studies, phase transitions in neuronal networks are almost driven by network parameters （e.g., external stimuli）, and there has been no investigation about the transitions between typical activity states of neuronal networks in a self-organized way by applying plastic connection weights. In this paper, we discuss phase transitions in electrically coupled and lattice-based small-world neuronal networks （LBSW networks） under spike-timing-dependent plasticity （STDP）. By applying STDP on all electrical synapses, various known and novel phase transitions could emerge in LBSW networks, particularly, the phenomenon of self-organized phase transitions （SOPTs）： repeated transitions between synchronous and asynchronous firing states. We further explore the mechanics generating SOPTs on the basis of synaptic weight dynamics.
基金the National Natural Science Foundation of China (No.19872079)the Fund of the Ministry of Education of China.
文摘Based on the assumption that a representative element of apearlitic steel is an aggregate of numerous spherical pearliticcolonies with randomly distributed orientations, and that each colonyis com- posed of many parallel fine lamellas of ferrite andcementite, a description for the dual-phase pearlitic steel isobtained by making use of a microstructure-based constitutiveequation for a single dual-phase pearlitic colony and the Hill'sself-consistent scheme. The elastoplastic response of dual-phasepearlitic steel BS11 subjected to asymmetrically cyclic loading isanalyzed, and a comparison with the experimental results showssatisfacto- ry agreement. The non-proportional cyclic plasticity ofBS11 is also analyzed, in which stress develops along a semi-circlein a biaxial tension/compression and shear stress plane, as istypically experienced by the sur- face elements in rolling andsliding contact.
基金Item Sponsored by National Natural Science Foundation of China(51201061,51475315)China Postdoctoral Science Foundation(2015M571804)Natural Science Foundation of Jiangsu Province of China(BK20150329)
文摘The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.
文摘The influence of deformation temperature,strain rate and alloying elements such as chromium,nickel,copper,on corrosion resistance of a 304 stainless steel after plastic deformation was investigated.The techniques employed were tensile test at room and elevated temperature,deep drawing tests at various strain rates,X-ray diffraction test and potentiodynamic and cyclic polarization,metallography by optical and scanning electron microscopy.Results showed that chromium,nickel and copper had a significant effect on corrosion resistance of steel after plastic deformation.It was observed that corrosion resistance after plastic deformation was a function of deformation temperature and alloying elements.
基金supported by the National Natural Science Foundation of China (Grant no. 11472262)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant no. XDB22040502)+1 种基金the Collaborative Innovation Center of Suzhou Nano Science and Technologythe Fundamental Research Funds for the Central Universities
文摘Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.
基金financially supported by Beijing Municipal Science and Technology Commission(No.Z131100003213019)National Natural Science Foundation of China(Nos.51101002 and 51301006)Beijing Municipal Commission of Education(Nos.KM201310005001 and KM201110005001)
文摘The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temperature.The microstructure and tensile properties of composites were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and tensile testing machine at room temperature.The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly.The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5 MPa,respectively,when the amount of I-phase particles added is10 %.Meanwhile,the elongation of the composites decreases sharply.
基金supported by the National Natural Science Foundation of China under Grant No. 51571192
文摘With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys(HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation behavior in these solid-solution alloys. It is shown that the maximum shear stress (max)required for dislocation nucleation is determined to be 1/16-1/12 and 1/18-1/14 of shear modulus for the TiZrNbTa and TiZrNbTaMo HEAs, respectively, which is nearly comparative to the theoretical shear stress of these alloys. The activation volumes of dislocation nucleation the TiZrNbTa and TiZrNbTaMo HEAs are determined to be 1.2 b^3 for and 1.3 b^3, respectively, which is substantially irrespective of alloying with Mo. Furthermore, activation volumes of these two HEAs are on the order of cubic burger’s vector and only one-third of the value for TiZrHfNb HEA, suggesting that a heterogeneous nucleation of dislocation took place in a way of direct atom-vacancy exchange, rather than of the cooperative motion of several atoms. These findings reveal the unique feature in deformation of BCC solid-solution complex alloys.
基金Project supported by the National Natural Science Foundation of China (No. 10502025)Fok Ying Tong Education Foundation (No.101005)University Foundation of Jiangsu Province (No.05KJB1300421)
文摘To determine the time-independent constitutive modeling for porous and multi- phase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated as a mixture of grain interior and grain bound- ary, and pores were taken as a single phase, then Budiansky＇s self-consistent method was used to calculate the Young＇s modulus of porous, possible multi-phase, nanocrystalline materials, the prediction being in good agreement with the results in the literature. Further, the established method is extended to simulate the constitutive relations of porous and possible multi-phase nanocrystalline materials with small plastic deformation in conjunction with the secant-moduli approach and iso-strain assumption. Comparisons between the experimental grain size and porosity dependent mechanical data and the corresponding predictions using the established model show that it appears to be capable of describing the time-independent mechanical behaviors for porous and multi-phase nanocrystalline materials in a small plastic strain range. Further discussion on the modification factor, the advantages and limitations of the model developed were present.
基金partly financially supported by the State Education Commission and the NNSF(No.49872071).
文摘Optical, cathodoluminescence and transmission electron microscope (TEM)analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclasticcoarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks showsimilar microstructural characteristics and give clues to similar processes of rock deformation.They are characterized by the structural contrast between macroscopic cataclastic (brittle) andmicroscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e.deformation twins, kink bands and microfractures) are well preserved in the deformed grains inclasts or in primary rocks. The matrix materials are of extremely fine grains with diffusivefeatures. Dislocation microstructures for co-existing brittle deformation and crystalline plasticitywere revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformedclasts, while dislocation walls form in the transitions to the fine-grained matrix materials andfree dislocations, dislocation loops and dislocation dipoles are observed both in the deformedclasts and in the fine-grained matrix materials. Dynamic recrystallization grains from subgrainrotation recrystallization and subsequent grain boundary migration constitute the major parts of thematrix materials. Statistical measurements of densities of free dislocations, grain sizes ofsubgrains and dynamically recrystallized grains suggest an unsteady state of the rock deformation.Microstructural and cathodoluminescence analyses prove that fluid activity is one of the major partsof faulting processes. Low-temperature plasticity, and thereby induced co-existence of macroscopicbrittle and microscopic ductile microstructures are attributed to hydrolytic weakening due to theinvolvement of fluid phases in deformation and subsequent variation of rock rheology. Duringhydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, andincrease the rate of recovery of strain-hardened rocks, which accommodates fracturing.
