The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercool...The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.展开更多
The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the ...The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.展开更多
The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also ...The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also carriedout to evaluate the effect of these processes on the room temperature mechanical properties. The experimentalresults of high temperature tensile tests revealed that the stress was inversely proportional to the square of the grainsize and that the activation energy for superplastic flow was higher than that for grain boundary diffusion.展开更多
The present study focuses on the relationship of hardness with grain size for commercially pure titanium （CpTi） and ultra fine grained titanium （UFG-Ti） produced by equal channel angular process （ECAP） of Cp-Ti...The present study focuses on the relationship of hardness with grain size for commercially pure titanium （CpTi） and ultra fine grained titanium （UFG-Ti） produced by equal channel angular process （ECAP） of Cp-Ti）.Vickers and Knoop indentations of UFG-Ti at different loads was ～2.5 times harder than those of Cp-Ti.Xray diffraction （XRD） analysis showed peak broadening in UFG-Ti due to reduced grain size and micro-lattice strains.Scanning electron microscopy （SEM） revealed that ECAP had reduced the grain size of Cp-Ti by ～10 times.Weibull statistics showed UFG-Ti with lower dispersion in hardness values compare to Cp-Ti indicating a more uniform microstructure.展开更多
Doping in Si nanocrystals is an interesting topic and directly studying the distribution of dopants in phosphorous/boron co-doping is an important issue facing the scientific community.In this study,atom probe tomogra...Doping in Si nanocrystals is an interesting topic and directly studying the distribution of dopants in phosphorous/boron co-doping is an important issue facing the scientific community.In this study,atom probe tomography is performed to study the structures and distribution of impurity in phosphorous/boron co-doped Si nanocrystals/SiO_(2) multilayers.Compared with phosphorous singly doped Si nanocrystals,it is interesting to find that the concentration of phosphorous in co-doped samples can be significantly improved.Theoretical simulation suggests that phosphorous-boron pairs are formed in co-doped Si nanocrystals with the lowest formation energy,which also reduces the formation energy of phosphorous in Si nanocrystals.The results indicate that co-doping can promote the entry of phosphorous impurities into the near-surface and inner sites of Si nanocrystals,which provides an interesting way to regulate the electronic and optical properties of Si nanocrystals such as the observed enhancement of conductivity and sub-band light emission.展开更多
The effects of aging treatment on the microstructures and mechanical properties of extruded AM50+xCa alloys （x=0,1%,2% in mass fraction） were studied. The results indicated the secondary phase Mg 17 Al 12 precipitat...The effects of aging treatment on the microstructures and mechanical properties of extruded AM50+xCa alloys （x=0,1%,2% in mass fraction） were studied. The results indicated the secondary phase Mg 17 Al 12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50+xCa alloys increased initially to its peak,and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature,the hardness of the AM50+2Ca alloy decreased,whereas the hardness of AM50 and AM50+1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50+1Ca alloys increased after aging treatment for the precipitation of Mg 17 Al 12 phase,which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature,their tensile strengths increased. For AM50+2Ca alloy,the tensile strength declined after aging at 150?℃ and 175?℃,while it increased slightly at 200?℃. The ductility of AM50+xCa alloys （x=0,1%,2%） declined after aging treatment.展开更多
Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active s...Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields,ranging from pattern formation in physical and chemical systems,to self-assembly problems in biology.Yet,very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions,and the link between model parameters and thermodynamic quantities is not established.Here,we report a modified phase field model that describes the subtlety of the ice vapour phase transition,through anisotropic water molecules attachment and condensation,surface diffusion,and strong anisotropic surface tension,that guarantee the anisotropy,faceting and dendritic growth of snowflakes.We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram.We find that the growth dynamics of snow crystals matches the selection theory,consistently with previous experimental observations.展开更多
A self-organisation is an universal phenomenon in nature and,in particular,is highly important in materials systems.Our goal was to develop a new theory that provides a computationally effective approach to this probl...A self-organisation is an universal phenomenon in nature and,in particular,is highly important in materials systems.Our goal was to develop a new theory that provides a computationally effective approach to this problem.In this paper a quasiparticle theory of a diffusional self-organisation of atoms in continuum space during the diffusional time scale has been introduced.This became possible due to two novelties,a concept of quasiparticles,fratons,used for a description of dynamic degrees of freedom and model Hamiltonian taking into account a directionality,length and strength of interatomic bonds.To illustrate a predictive power and achievable level of complexity of self-assembled structures,the challenging cases of self-assembling of the diamond,zinc-blende,helix and double-helix structures,from a random atomic distribution,have been successfully modelled.This approach opens a way to model a self-assembling of complex atomic and molecular structures in the atomic scale during diffusional time.展开更多
Electrical characterization analyses are proposed in this work using the Lambert function on Schottky junctions in GaN wide band gap semiconductor devices for extraction of physical parameters.The Lambert function is ...Electrical characterization analyses are proposed in this work using the Lambert function on Schottky junctions in GaN wide band gap semiconductor devices for extraction of physical parameters.The Lambert function is used to give an explicit expression of the current in the Schottky junction.This function is applied with defined conduction phenomena,whereas other work presented arbitrary（or undefined）conduction mechanisms in such parameters＇ extractions.Based upon AlGaN/GaN HEMT structures,extractions of parameters are undergone in order to provide physical characteristics.This work highlights a new expression of current with defined conduction phenomena in order to quantify the physical properties of Schottky contacts in AlGaN/GaN HEMT transistors.展开更多
文摘The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.
基金This work was financially supported by the International Cooperation Foundation of Shanghai Science and Technology Committee of China (No. 02SL002) and the Regional Council of Rhone-Alpes of France.
文摘The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.
基金The autlors gratefully acknowledge the financial support from the National Commnittee for High Technology ResearchDevelopment of China under the project No.2002AA331120.
文摘The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also carriedout to evaluate the effect of these processes on the room temperature mechanical properties. The experimentalresults of high temperature tensile tests revealed that the stress was inversely proportional to the square of the grainsize and that the activation energy for superplastic flow was higher than that for grain boundary diffusion.
文摘The present study focuses on the relationship of hardness with grain size for commercially pure titanium （CpTi） and ultra fine grained titanium （UFG-Ti） produced by equal channel angular process （ECAP） of Cp-Ti）.Vickers and Knoop indentations of UFG-Ti at different loads was ～2.5 times harder than those of Cp-Ti.Xray diffraction （XRD） analysis showed peak broadening in UFG-Ti due to reduced grain size and micro-lattice strains.Scanning electron microscopy （SEM） revealed that ECAP had reduced the grain size of Cp-Ti by ～10 times.Weibull statistics showed UFG-Ti with lower dispersion in hardness values compare to Cp-Ti indicating a more uniform microstructure.
基金Project supported by the National Key Research and Development Program of China (Grant No.2018YFB2200101)the National Natural Science Foundation of China (Grant Nos.62004078 and 61921005)+4 种基金Natural Science Foundation of Jiangsu Province (Grant No.BK20201073)Natural Science Foundation of Ningbo (Grant No.2021J068)ANR DONNA (Grant No.ANR-18-CE09-0034)Leading Innovative and Entrepreneur Team Introduction Program of Hangzhou (Grant No.TD2022012)partially supported by the CNRS Federation IRMA-FR 3095。
文摘Doping in Si nanocrystals is an interesting topic and directly studying the distribution of dopants in phosphorous/boron co-doping is an important issue facing the scientific community.In this study,atom probe tomography is performed to study the structures and distribution of impurity in phosphorous/boron co-doped Si nanocrystals/SiO_(2) multilayers.Compared with phosphorous singly doped Si nanocrystals,it is interesting to find that the concentration of phosphorous in co-doped samples can be significantly improved.Theoretical simulation suggests that phosphorous-boron pairs are formed in co-doped Si nanocrystals with the lowest formation energy,which also reduces the formation energy of phosphorous in Si nanocrystals.The results indicate that co-doping can promote the entry of phosphorous impurities into the near-surface and inner sites of Si nanocrystals,which provides an interesting way to regulate the electronic and optical properties of Si nanocrystals such as the observed enhancement of conductivity and sub-band light emission.
文摘The effects of aging treatment on the microstructures and mechanical properties of extruded AM50+xCa alloys （x=0,1%,2% in mass fraction） were studied. The results indicated the secondary phase Mg 17 Al 12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50+xCa alloys increased initially to its peak,and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature,the hardness of the AM50+2Ca alloy decreased,whereas the hardness of AM50 and AM50+1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50+1Ca alloys increased after aging treatment for the precipitation of Mg 17 Al 12 phase,which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature,their tensile strengths increased. For AM50+2Ca alloy,the tensile strength declined after aging at 150?℃ and 175?℃,while it increased slightly at 200?℃. The ductility of AM50+xCa alloys （x=0,1%,2%） declined after aging treatment.
基金financial support through the CISTIC project of programme Investissements d’Avenir LabEx EMC3(ANR-10-LABX-09-01).
文摘Snowflake growth provides a fascinating example of spontaneous pattern formation in nature.Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields,ranging from pattern formation in physical and chemical systems,to self-assembly problems in biology.Yet,very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions,and the link between model parameters and thermodynamic quantities is not established.Here,we report a modified phase field model that describes the subtlety of the ice vapour phase transition,through anisotropic water molecules attachment and condensation,surface diffusion,and strong anisotropic surface tension,that guarantee the anisotropy,faceting and dendritic growth of snowflakes.We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram.We find that the growth dynamics of snow crystals matches the selection theory,consistently with previous experimental observations.
基金supported in part by the grant from the French National Agency for the Research(ANR)project‘Spiderman’.
文摘A self-organisation is an universal phenomenon in nature and,in particular,is highly important in materials systems.Our goal was to develop a new theory that provides a computationally effective approach to this problem.In this paper a quasiparticle theory of a diffusional self-organisation of atoms in continuum space during the diffusional time scale has been introduced.This became possible due to two novelties,a concept of quasiparticles,fratons,used for a description of dynamic degrees of freedom and model Hamiltonian taking into account a directionality,length and strength of interatomic bonds.To illustrate a predictive power and achievable level of complexity of self-assembled structures,the challenging cases of self-assembling of the diamond,zinc-blende,helix and double-helix structures,from a random atomic distribution,have been successfully modelled.This approach opens a way to model a self-assembling of complex atomic and molecular structures in the atomic scale during diffusional time.
基金Project supported by the French Department of Defense(DGA)
文摘Electrical characterization analyses are proposed in this work using the Lambert function on Schottky junctions in GaN wide band gap semiconductor devices for extraction of physical parameters.The Lambert function is used to give an explicit expression of the current in the Schottky junction.This function is applied with defined conduction phenomena,whereas other work presented arbitrary（or undefined）conduction mechanisms in such parameters＇ extractions.Based upon AlGaN/GaN HEMT structures,extractions of parameters are undergone in order to provide physical characteristics.This work highlights a new expression of current with defined conduction phenomena in order to quantify the physical properties of Schottky contacts in AlGaN/GaN HEMT transistors.
