The transformation mechanism of the inclusions and microstructure in 316L stainless steel after post-isothermal heat treatment(IHT)was revealed,along with the pitting behavior of the inclusions in a chloride environme...The transformation mechanism of the inclusions and microstructure in 316L stainless steel after post-isothermal heat treatment(IHT)was revealed,along with the pitting behavior of the inclusions in a chloride environment before and after the transformation.The effect of the inclusion transformation on the pitting corrosion behavior of 316L stainless steel and its intrinsic mechanism was also revealed.Results revealed a gradual transformation of MnO-SiO_(2)inclusions into MnO-Cr_(2)O_(3) within the temperature range of 1373 to 1573 K.MnO-Cr_(2)O_(3)inclusions exhibited minimal dissolution in chloride ion corrosion environments,while MnO-SiO_(2)oxides demonstrated higher electrochemical activity and were more prone to dissolve and form pits.Meanwhile,IHT significantly reduced the dislocation density of stainless steel,rendering it more stable in corrosive environments.X-ray photoelectron spectroscopy peak distributions of the passive films demonstrated that IHT increased the proportion of Cr and Fe oxides and hydroxides in the passive film which improved the stability and corrosion resistance of the steel.展开更多
Silicomanganese dust contains large amounts of valuables,such as Si and Mn,which can be used as raw materials for the smelting of silicomanganese.However,the direct addition of dust to the submerged arc furnace can in...Silicomanganese dust contains large amounts of valuables,such as Si and Mn,which can be used as raw materials for the smelting of silicomanganese.However,the direct addition of dust to the submerged arc furnace can influence the permeability of burden due to the fine particle size of dust,which results in incomplete reduction reactions during the smelting process.In this paper,silicomanganese dust,graphite powder,and other additives were pressed to form carbon-containing dust briquettes,and the self-reduction process of the dust briquettes was investigated through the isothermal thermogravimetric method with different carbon–oxygen (C/O) molar ratios,contents of fluxing agents,and reduction temperatures.Various reduction kinetic models for dust briquettes at different temperatures were established.The results show that the reaction fraction of the dust briquettes was about 90%at a C/O molar ratio of 1.2 with optimal reduction efficiency.The addition of CaF_(2)contributed to the decrease in the melting point and viscosity of dust briquettes,which increased their reduction rate.As the reduction temperature increased,the reduction rate of dust briquettes increased.The reduction reaction rate of dust briquettes was controlled through gas-phase diffusion.Meanwhile,their reduction process was analyzed kinetically,with the reaction time of 5 min as the dividing line.The apparent activation energies for the two diffusion stages were 56.10 and 100.52 kJ/mol,respectively.The kinetic equations are expressed as[1-(1-f)^(1/3)]^(2)=0.69e^(-56100/(RT))t and [1-(1-f)^(1/3)]^(2)=2.06e^(-100520/(RT))t.展开更多
The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through ...The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.展开更多
Semicrystalline polymers usually undergo multilevel microstructural evolutions with annealing and stretching processes,which is es-sential to tailor the physical properties of the polymer.Here,poly(butylene carbonate)...Semicrystalline polymers usually undergo multilevel microstructural evolutions with annealing and stretching processes,which is es-sential to tailor the physical properties of the polymer.Here,poly(butylene carbonate)(PBC)sheets were prepared via isothermal annealing and unidirectional pre-stretching processes,then the changes of PBC in crystallinity,mechanical properties,thermal properties and microscopic changes before and after annealing and stretching were measured,as well as the relationship between microstructure and macroscopic proper-ties before and after stretching.The strengthening mechanism of PBC was also described.It was demonstrated that shish-kabab structure emerged under the pre-stretching process.With the increase of the tensile ratio,the crystallinity,structure and mechanical properties are in-creased differently.Among them,the crystallinity and tensile strength after annealing-stretching treatment increased to 24.45%and 104.5 MPa,respectively,which were about 1.55 times and 3.4 times of those-without any treatment.展开更多
The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was a...The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was analyzed using the first-order irreversible reaction,following the shrinking unreacted nucleus model.The results demonstrate that VTM pellets prepared with 3Co-binder exhibit a faster oxidation rate than those with F-binder across the temperatures ranging from 1073 to 1473 K.In both cases,the oxidation process was controlled by an interfacial chemical reaction during the pre-oxidation stage and by internal diffusion during the mid-oxidation stage.The type of binder did not influence the primary oxidation control mechanism of the VTM pellets.However,the apparent rate constants in the pre-oxidation stage and the internal diffusion coefficients in the mid-oxidation stage were higher for pellets with 3Co-binder compared to those with F-binder.The apparent activation energies for the 3Co-binder pellets were similar to those of bentonite,indicating favorable kinetic conditions without negative impacts on the oxidation process.Nonetheless,it is important to note that pellets with F-binder required a longer oxidation time than those with 3Co-binder.展开更多
The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index met...The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.展开更多
Based on the entropy function, a two-dimensional phase field model of binary alloys was established. Meanwhile, an explicit difference method with uniform grid was adopted to solve the phase field and solute field con...Based on the entropy function, a two-dimensional phase field model of binary alloys was established. Meanwhile, an explicit difference method with uniform grid was adopted to solve the phase field and solute field controlled equations. And the alternating direction implicit(ADI) algorithm for solving temperature field controlled equation was also employed to avoid the restriction of time step. Some characteristics of the Ni-Cu alloy were captured in the process of non-isothermal solidification, and the comparative analysis of the isothermal and the non-isothermal solidification was investigated. The simulation results indicate that the non-isothermal model is favorable to simulate the real solidification process of binary alloys, and when the thermal diffusivity decreases, the non-isothermal phase-field model is gradually consistent with the isothermal phase-field model.展开更多
Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is ...Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.展开更多
Different amounts of Fe(0.005,0.01,0.03,0.05,and 0.07 wt%)were added to SAC305 to study the shear behavior damage of Fe-doped SAC solder joints under thermal loading(170℃,holding time of 0,250,500,and 750 h).The resu...Different amounts of Fe(0.005,0.01,0.03,0.05,and 0.07 wt%)were added to SAC305 to study the shear behavior damage of Fe-doped SAC solder joints under thermal loading(170℃,holding time of 0,250,500,and 750 h).The results show that during isothermal aging at 170℃,the average shear force of all solder joints decreases with increasing aging time,while the average fracture energy first increases and then decreases,reaching a maximum at 500 h.Minor Fe doping could both increase shear forces and related fracture energy,with the optimum Fe doping amount being 0.03 wt%within the entire aging range.This is because the doping Fe reduces the undercooling of the SAC305 alloy,resulting in the microstructure refining of solder joints.This in turn causes the microstructure changing from network structure(SAC305 joint:eutectic network+β-Sn)to a single matrix structure(0.03Fe-doped SAC305 joint:β-Sn matrix+small compound particles).Specifically,Fe atoms can replace some Cu in Cu_(6)Sn_(5)(both inside the solder joint and at the interface),and then form(Cu,Fe)_(6)Sn_(5) compounds,resulting in an increase in the elastic modulus and nanohardness of the compounds.Moreover,the growth of Cu_(6)Sn_(5) and Cu_(3)Sn intermetallic compounds(IMC)layer are inhibited by Fe doping even after the aging time prolonging,and Fe aggregates near the interface compound to form FeSn_(2).This study is of great significance for controlling the growth of interfacial compounds,stabilizing the microstructures,and providing strengthening strategy for solder joint alloy design.展开更多
Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in AI-2-mole-%-Si binary ...Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in AI-2-mole-%-Si binary alloy under isothermal solidification was simulated using phase field model. The simulation results showed the impingement of arbitrarily oriented crystals and the competitive growth among the grains during solidification. With the increase of growing time, the grains begin to coalesce and impinge the adjacent grains. When the dendrites start to impinge, the dendrite growth is obviously inhibited.展开更多
Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of ...Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of 0.8. The experimental results show that the flow stress increases with the decrease in the deformation temperature and the increase in the strain rate. The apparent activation energy for deformation is much lower at lower strain rates than that at higher strain rates. The flow stress model considering strain compensation was established. The average relative error between the calculated flow stress and experimental results is about 7.69%, indicating that the present model could be used to accurately predict the flow stress during high temperature in α＋β phase field of TC4 alloy.展开更多
Transient liquid phase(TLP)bonding is a promising process for the joining and repairing of nickel-base superalloys.One of the most important parameters in TLP bonding is the bonding time required for suf-ficient isoth...Transient liquid phase(TLP)bonding is a promising process for the joining and repairing of nickel-base superalloys.One of the most important parameters in TLP bonding is the bonding time required for suf-ficient isothermal solidification which prevents the formation of undesirable precipitated phases.In the present work,the effect of bonding time on the microstructure,type,and evolution of precipitates in the non-isothermal solidified zone(NSZ)and their effect on micro-mechanical properties were systemat-ically investigated using multi-scale tests in TLP bonded Mar-M247 superalloy joints with Ni-15.2Cr-3.74B interlayer at 1230℃.For a bonding time of 5 min,dual-phase M_(23)(C,B)_(6)-γ/γ’(where M is a mix-ture of Hf,Ta,Cr,and Ni)with eutectic configuration was formed in NSZ.With the increase in bonding time,the evolution of NSZ microstructure can be summed up as eutectic M_(23)(C,B)_(6)-γ/γ’,semi-striping dual-phase M_(23)(C,B)_(6)-γ/γ’,discontinuously striping M_(23)(C,B)_(6)-γ/γ’,followed by the disintegration of NSZ.As the NSZ counterpart,the isothermal solidified zone(ISZ)is mainly composed ofγ/γ’.Ac-companied by the dissolution of M_(23)(C,B)_(6) in the centerline,the proportion of the ISZ increases greatly until the joints are completely occupied by ISZ.Finally,a bamboo-like structure with domain size of-100μm was formed in the joint centerline,along withγ’reorganized themselves all into cubic shapes and distributed homogeneously.Mechanical property tests demonstrated that in comparison to samples with longer bonding time,the NSZ of the shortest bonding time(5 min)has the highest strength and a subsequent decrease in strength was observed with prolonging the bonding time and post-bond heat treatment.Furthermore,possible solidification/transformation path,segregation behavior,and formation mechanism of NSZ/ISZ evolution were discussed.展开更多
The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated ...The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated using dilatometry,scanning electron microscopy,transmission electron microscopy(TEM),and X-ray diffraction.The results show that the microstructures of CH steel with 0.3 wt.%Cr are ferrite,granular bainite,martensite,and retained austenite,while no ferrite is observed in the microstructure of CH steel with 1.0 wt.%Cr in the same process.Cr promotes the precipitation of(Nb,Ti)C in the high-temperature austenite region through theoretical calculations and TEM observations.Cr retards the bainite transformation and refines the grain size of CH steel.Furthermore,as isothermal holding temperature increases from 400 to 480℃,the bainite and retained austenite fractions of two CH steels decrease,while the martensite fraction increases in the steels after final quenching.Consequently,the strength has an increasing tendency and the total elongation has a decreasing tendency with increasing isothermal temperature.展开更多
Zabuye Salt Lake in Tibet,China is a carbonate-type salt lake,which has some unique characteristics that make it different from other types of salt lakes.The lake is at the latter period in its evolution and contains ...Zabuye Salt Lake in Tibet,China is a carbonate-type salt lake,which has some unique characteristics that make it different from other types of salt lakes.The lake is at the latter period in its evolution and contains liquid and solid resources.Its brine is rich in Li,B,K and other useful minor elements that are of great economic value.We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15℃and 25℃.The crystallization sequence of the primary salts from the brine at 25℃is halite（NaCl）→aphthitalite （3K_2SO_4·Na_2SO_4）→zabuyelite（Li_2CO_3）→trona（Na_2CO_3·NaHCO_3·2H_2O）→thermonatrite （Na_2CO_3·H_2O）→sylvite（KCl）,while the sequence is halite（NaCl）→sylvite（KCl）→trona （Na_2CO_3·NaHCO_3·2H_2O）→zabuyelite（Li_2CO_3）→thermonatrite（Na_2CO_3·H_2O）→aphthitalite （3K_2SO_4·Na_2SO_4） at 15℃.They are in accordance with the metastable phase diagram of the Na~＋,K~＋-Cl^-, CO_3^（2-）,SO_4^（2-）-H_2O quinary system at 25℃,except for Na_2CO_3·7H_2O which is replaced by trona and thermonatrite.In the 25℃experiment,zabuyelite（Li_2CO_3） was precipitated in the early stage because Li_2CO_3 is supersaturated in the brine at 25℃,in contrast with that at 15℃,it precipitated in the later stage.Potash was precipitated in the middle and late stages in both experiments,while boron was concentrated in the early and middle stages and precipitated in the late stage.展开更多
A new phase field method for two-dimensional simulations of binary alloy solidification was studied. A model basing on solute conservative in every unit was developed for solving the solute diffusion equation during s...A new phase field method for two-dimensional simulations of binary alloy solidification was studied. A model basing on solute conservative in every unit was developed for solving the solute diffusion equation during solidification. Two-dimensional computations were performed for ideal solutions and Ni-Cu dendritic growth into an isothermal and highly supersaturated liquid phase.展开更多
Dendritic coarsening in AI-2mol%Si alloy during isothermal solidification at 880K was investigated by phase field modeling. Three coarsening mechanisms operate in the alloy： （a） melting of small dendrite arms; （b...Dendritic coarsening in AI-2mol%Si alloy during isothermal solidification at 880K was investigated by phase field modeling. Three coarsening mechanisms operate in the alloy： （a） melting of small dendrite arms; （b） coalescence of dendrites near the tips leading to the entrapment of liquid droplets; （c） smoothing of dendrites. Dendrite melting is found to be dominant in the stage of dendritic growth, whereas coalescence of dendrites and smoothing of dendrites are dominant during isothermal holding. The simulated results provide a better understanding of dendrite coarsening during isothermal solidification.展开更多
The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd(x=0,1.5 wt.%,2.0 wt.%and 2.5 wt.%)magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work.Results sh...The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd(x=0,1.5 wt.%,2.0 wt.%and 2.5 wt.%)magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work.Results showed that the lamellar(Mg,Al)3Gd phases transformed into the particle-like Al2Gd phases in AZ31 magnesium alloys with Gd addition during semi-solid isothermal heat treatment,leading to yielding more sphericalα-Mg grains.When Gd content is 2.0 wt.%,the size of semi-solid spherical grains reaches the minimum.The main mechanism of grain refinement lies in the remelting of dendritic branches as well as the auxiliary effect of a small number of Al2Gd particles as grain refining inoculants.Meanwhile,Al2Gd particles enriched at the solid-liquid interfaces can remarkably retard the growth rate ofα-Mg grains.A reduction of deformation resistance has been successfully achieved in AZ31-2.0Gd magnesium alloy after semi-solid isothermal heat treatment,which shows a moderate compressive deformation resistance(230 MPa),comparing to the as-cast AZ31 magnesium alloy(280 MPa)and semi-solid AZ31 magnesium alloy(209 MPa).展开更多
In this work, the non-isothermal dissolution kinetics of the sigma phase in duplex stainless steels has been studied and modelled. A semi-empirical model is proposed to describe the kinetics of sigma phase precipitati...In this work, the non-isothermal dissolution kinetics of the sigma phase in duplex stainless steels has been studied and modelled. A semi-empirical model is proposed to describe the kinetics of sigma phase precipitation/dissolution during continuous heating starting from the isothermal transformation kinetics. The proposed model, which presumes validity of the additivity rule, is validated by means of experimental investigations. A good agreement is found between experimental and analytical results.展开更多
The evolution and distribution of Al2Sm phase in as-extruded AZ61-xSm（x=0, 1.5, 2.0 and 2.5, mass fraction, %） magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that ...The evolution and distribution of Al2Sm phase in as-extruded AZ61-xSm（x=0, 1.5, 2.0 and 2.5, mass fraction, %） magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0%（mass fraction）, the average size of the globular grains reached the smallest value of 90 μm. Although a few Al2Sm particles existed in the α-Mg grains, most of Al2Sm particles solidified at the edge of the globular grains with the width of 20 μm. These phenomena are mainly attributed to the forces acting on Al2Sm particles in front of the solid-liquid interface, leading to Al2Sm particles accumulating at the solid-liquid interface and then solidifying at the edge of the globular grains in the quenching process.展开更多
基金the support from the National Natural Science Foundation of China(Grant Nos.52074198,52374342,and U21A20113)the Department of Science and Technology of Hubei Province(Grant Nos.2023AFB603 and 2023DJC140).
文摘The transformation mechanism of the inclusions and microstructure in 316L stainless steel after post-isothermal heat treatment(IHT)was revealed,along with the pitting behavior of the inclusions in a chloride environment before and after the transformation.The effect of the inclusion transformation on the pitting corrosion behavior of 316L stainless steel and its intrinsic mechanism was also revealed.Results revealed a gradual transformation of MnO-SiO_(2)inclusions into MnO-Cr_(2)O_(3) within the temperature range of 1373 to 1573 K.MnO-Cr_(2)O_(3)inclusions exhibited minimal dissolution in chloride ion corrosion environments,while MnO-SiO_(2)oxides demonstrated higher electrochemical activity and were more prone to dissolve and form pits.Meanwhile,IHT significantly reduced the dislocation density of stainless steel,rendering it more stable in corrosive environments.X-ray photoelectron spectroscopy peak distributions of the passive films demonstrated that IHT increased the proportion of Cr and Fe oxides and hydroxides in the passive film which improved the stability and corrosion resistance of the steel.
基金financially supported by the Hubei Provincial Key Laboratory for New Processes of Ironmaking and Steelmaking (No. KF-20-3)Shandong Postdoctoral Science Foundation, China (No. SDCX-ZG-202301014)。
文摘Silicomanganese dust contains large amounts of valuables,such as Si and Mn,which can be used as raw materials for the smelting of silicomanganese.However,the direct addition of dust to the submerged arc furnace can influence the permeability of burden due to the fine particle size of dust,which results in incomplete reduction reactions during the smelting process.In this paper,silicomanganese dust,graphite powder,and other additives were pressed to form carbon-containing dust briquettes,and the self-reduction process of the dust briquettes was investigated through the isothermal thermogravimetric method with different carbon–oxygen (C/O) molar ratios,contents of fluxing agents,and reduction temperatures.Various reduction kinetic models for dust briquettes at different temperatures were established.The results show that the reaction fraction of the dust briquettes was about 90%at a C/O molar ratio of 1.2 with optimal reduction efficiency.The addition of CaF_(2)contributed to the decrease in the melting point and viscosity of dust briquettes,which increased their reduction rate.As the reduction temperature increased,the reduction rate of dust briquettes increased.The reduction reaction rate of dust briquettes was controlled through gas-phase diffusion.Meanwhile,their reduction process was analyzed kinetically,with the reaction time of 5 min as the dividing line.The apparent activation energies for the two diffusion stages were 56.10 and 100.52 kJ/mol,respectively.The kinetic equations are expressed as[1-(1-f)^(1/3)]^(2)=0.69e^(-56100/(RT))t and [1-(1-f)^(1/3)]^(2)=2.06e^(-100520/(RT))t.
基金supported by the National Natural Science Foundation of China(No.52204302)Young Elite Scientist Sponsorship Program by CAST(No.YESS20220533)+1 种基金Hunan Provincial Natural Science Foundation of China(No.2022JJ50274)China Baowu Low Carbon Metallurgy Innovation Foundation(No.BWLCF202103).
文摘The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.
基金supported by the Sichuan Provincial Regional Innovation Cooperation Project(No.2024YFHZ0159).
文摘Semicrystalline polymers usually undergo multilevel microstructural evolutions with annealing and stretching processes,which is es-sential to tailor the physical properties of the polymer.Here,poly(butylene carbonate)(PBC)sheets were prepared via isothermal annealing and unidirectional pre-stretching processes,then the changes of PBC in crystallinity,mechanical properties,thermal properties and microscopic changes before and after annealing and stretching were measured,as well as the relationship between microstructure and macroscopic proper-ties before and after stretching.The strengthening mechanism of PBC was also described.It was demonstrated that shish-kabab structure emerged under the pre-stretching process.With the increase of the tensile ratio,the crystallinity,structure and mechanical properties are in-creased differently.Among them,the crystallinity and tensile strength after annealing-stretching treatment increased to 24.45%and 104.5 MPa,respectively,which were about 1.55 times and 3.4 times of those-without any treatment.
基金supported by National Natural Science Foundation of China(No.52204302)Young Elite Scientist Sponsorship Program by CAST(No.YESS20220533)Hunan Provincial Natural Science Foundation of China(No.2022JJ40625).
文摘The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was analyzed using the first-order irreversible reaction,following the shrinking unreacted nucleus model.The results demonstrate that VTM pellets prepared with 3Co-binder exhibit a faster oxidation rate than those with F-binder across the temperatures ranging from 1073 to 1473 K.In both cases,the oxidation process was controlled by an interfacial chemical reaction during the pre-oxidation stage and by internal diffusion during the mid-oxidation stage.The type of binder did not influence the primary oxidation control mechanism of the VTM pellets.However,the apparent rate constants in the pre-oxidation stage and the internal diffusion coefficients in the mid-oxidation stage were higher for pellets with 3Co-binder compared to those with F-binder.The apparent activation energies for the 3Co-binder pellets were similar to those of bentonite,indicating favorable kinetic conditions without negative impacts on the oxidation process.Nonetheless,it is important to note that pellets with F-binder required a longer oxidation time than those with 3Co-binder.
基金Projects (50831003, 50571037) supported by the National Natural Science Foundation of China
文摘The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.
基金Projects(51161011,11364024)supported by the National Natural Science Foundation of China
文摘Based on the entropy function, a two-dimensional phase field model of binary alloys was established. Meanwhile, an explicit difference method with uniform grid was adopted to solve the phase field and solute field controlled equations. And the alternating direction implicit(ADI) algorithm for solving temperature field controlled equation was also employed to avoid the restriction of time step. Some characteristics of the Ni-Cu alloy were captured in the process of non-isothermal solidification, and the comparative analysis of the isothermal and the non-isothermal solidification was investigated. The simulation results indicate that the non-isothermal model is favorable to simulate the real solidification process of binary alloys, and when the thermal diffusivity decreases, the non-isothermal phase-field model is gradually consistent with the isothermal phase-field model.
基金supported by the opening fund of National Key Research and Development Program of China(No.2020YFE0205300)Key Laboratory of Science and Technology on Silicon Devices,Chinese Academy of Sciences(No.KLSDTJJ2022-5)+1 种基金Chongqing Natural Science Foundation of China(No.cstc2021jcyj-msxmX1002)the Fundamental Research Funds for the Central Universities(No.AUGA5710051221).
文摘Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.
基金supported by the Yunnan Fundamental Research Projects(No.202301BC070001-001)funded by the Yunnan Provincial Department of Science and Technologythe Yunnan Provincial Science and Technology Plan Project(No.202005AF150045)+1 种基金the Jiangsu Province Industry-University-Research Cooperation Project(No.BY2022832)funded by the Jiangsu Provincial Department of Science and Technologythe National Natural Science Foundation of China(No.52275339).
文摘Different amounts of Fe(0.005,0.01,0.03,0.05,and 0.07 wt%)were added to SAC305 to study the shear behavior damage of Fe-doped SAC solder joints under thermal loading(170℃,holding time of 0,250,500,and 750 h).The results show that during isothermal aging at 170℃,the average shear force of all solder joints decreases with increasing aging time,while the average fracture energy first increases and then decreases,reaching a maximum at 500 h.Minor Fe doping could both increase shear forces and related fracture energy,with the optimum Fe doping amount being 0.03 wt%within the entire aging range.This is because the doping Fe reduces the undercooling of the SAC305 alloy,resulting in the microstructure refining of solder joints.This in turn causes the microstructure changing from network structure(SAC305 joint:eutectic network+β-Sn)to a single matrix structure(0.03Fe-doped SAC305 joint:β-Sn matrix+small compound particles).Specifically,Fe atoms can replace some Cu in Cu_(6)Sn_(5)(both inside the solder joint and at the interface),and then form(Cu,Fe)_(6)Sn_(5) compounds,resulting in an increase in the elastic modulus and nanohardness of the compounds.Moreover,the growth of Cu_(6)Sn_(5) and Cu_(3)Sn intermetallic compounds(IMC)layer are inhibited by Fe doping even after the aging time prolonging,and Fe aggregates near the interface compound to form FeSn_(2).This study is of great significance for controlling the growth of interfacial compounds,stabilizing the microstructures,and providing strengthening strategy for solder joint alloy design.
基金supported by the Doctor Foundational Research Project in Shenyang Ligong University(Serial Number:0010).
文摘Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in AI-2-mole-%-Si binary alloy under isothermal solidification was simulated using phase field model. The simulation results showed the impingement of arbitrarily oriented crystals and the competitive growth among the grains during solidification. With the increase of growing time, the grains begin to coalesce and impinge the adjacent grains. When the dendrites start to impinge, the dendrite growth is obviously inhibited.
基金financially supported by China Postdoctoral Science Foundation (No. 2017M610649)Fundamental Research Funds for the Central Universities (No. 3102017zy001)
文摘Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of 0.8. The experimental results show that the flow stress increases with the decrease in the deformation temperature and the increase in the strain rate. The apparent activation energy for deformation is much lower at lower strain rates than that at higher strain rates. The flow stress model considering strain compensation was established. The average relative error between the calculated flow stress and experimental results is about 7.69%, indicating that the present model could be used to accurately predict the flow stress during high temperature in α＋β phase field of TC4 alloy.
基金supported by the National Natural Science Foundation of China(No.52125101)the Basic and Applied Basic Research Major Program of Guangdong Province,China(Grant No.2021B0301030003)the Jihua Laboratory(Project No.X210141TL210).
文摘Transient liquid phase(TLP)bonding is a promising process for the joining and repairing of nickel-base superalloys.One of the most important parameters in TLP bonding is the bonding time required for suf-ficient isothermal solidification which prevents the formation of undesirable precipitated phases.In the present work,the effect of bonding time on the microstructure,type,and evolution of precipitates in the non-isothermal solidified zone(NSZ)and their effect on micro-mechanical properties were systemat-ically investigated using multi-scale tests in TLP bonded Mar-M247 superalloy joints with Ni-15.2Cr-3.74B interlayer at 1230℃.For a bonding time of 5 min,dual-phase M_(23)(C,B)_(6)-γ/γ’(where M is a mix-ture of Hf,Ta,Cr,and Ni)with eutectic configuration was formed in NSZ.With the increase in bonding time,the evolution of NSZ microstructure can be summed up as eutectic M_(23)(C,B)_(6)-γ/γ’,semi-striping dual-phase M_(23)(C,B)_(6)-γ/γ’,discontinuously striping M_(23)(C,B)_(6)-γ/γ’,followed by the disintegration of NSZ.As the NSZ counterpart,the isothermal solidified zone(ISZ)is mainly composed ofγ/γ’.Ac-companied by the dissolution of M_(23)(C,B)_(6) in the centerline,the proportion of the ISZ increases greatly until the joints are completely occupied by ISZ.Finally,a bamboo-like structure with domain size of-100μm was formed in the joint centerline,along withγ’reorganized themselves all into cubic shapes and distributed homogeneously.Mechanical property tests demonstrated that in comparison to samples with longer bonding time,the NSZ of the shortest bonding time(5 min)has the highest strength and a subsequent decrease in strength was observed with prolonging the bonding time and post-bond heat treatment.Furthermore,possible solidification/transformation path,segregation behavior,and formation mechanism of NSZ/ISZ evolution were discussed.
基金The authors gratefully acknowledge the support from the Key Research and Development Plan of Shandong Province(No.2019TSLH0103)the New Energy Automobile Material Production and Application Demonstration Platform Project(No.TC180A6MR-1)Guangxi Innovation-Driven Development Special Fund Project(No.AA18242012).
文摘The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated using dilatometry,scanning electron microscopy,transmission electron microscopy(TEM),and X-ray diffraction.The results show that the microstructures of CH steel with 0.3 wt.%Cr are ferrite,granular bainite,martensite,and retained austenite,while no ferrite is observed in the microstructure of CH steel with 1.0 wt.%Cr in the same process.Cr promotes the precipitation of(Nb,Ti)C in the high-temperature austenite region through theoretical calculations and TEM observations.Cr retards the bainite transformation and refines the grain size of CH steel.Furthermore,as isothermal holding temperature increases from 400 to 480℃,the bainite and retained austenite fractions of two CH steels decrease,while the martensite fraction increases in the steels after final quenching.Consequently,the strength has an increasing tendency and the total elongation has a decreasing tendency with increasing isothermal temperature.
基金supported by project of K0722 from the Institute of Mineral Resources,Chinese Academy of Geological Sciences
文摘Zabuye Salt Lake in Tibet,China is a carbonate-type salt lake,which has some unique characteristics that make it different from other types of salt lakes.The lake is at the latter period in its evolution and contains liquid and solid resources.Its brine is rich in Li,B,K and other useful minor elements that are of great economic value.We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15℃and 25℃.The crystallization sequence of the primary salts from the brine at 25℃is halite（NaCl）→aphthitalite （3K_2SO_4·Na_2SO_4）→zabuyelite（Li_2CO_3）→trona（Na_2CO_3·NaHCO_3·2H_2O）→thermonatrite （Na_2CO_3·H_2O）→sylvite（KCl）,while the sequence is halite（NaCl）→sylvite（KCl）→trona （Na_2CO_3·NaHCO_3·2H_2O）→zabuyelite（Li_2CO_3）→thermonatrite（Na_2CO_3·H_2O）→aphthitalite （3K_2SO_4·Na_2SO_4） at 15℃.They are in accordance with the metastable phase diagram of the Na~＋,K~＋-Cl^-, CO_3^（2-）,SO_4^（2-）-H_2O quinary system at 25℃,except for Na_2CO_3·7H_2O which is replaced by trona and thermonatrite.In the 25℃experiment,zabuyelite（Li_2CO_3） was precipitated in the early stage because Li_2CO_3 is supersaturated in the brine at 25℃,in contrast with that at 15℃,it precipitated in the later stage.Potash was precipitated in the middle and late stages in both experiments,while boron was concentrated in the early and middle stages and precipitated in the late stage.
基金the National Natural Science Foundation of China financially(Grant No.10176009)
文摘A new phase field method for two-dimensional simulations of binary alloy solidification was studied. A model basing on solute conservative in every unit was developed for solving the solute diffusion equation during solidification. Two-dimensional computations were performed for ideal solutions and Ni-Cu dendritic growth into an isothermal and highly supersaturated liquid phase.
基金financially supported by the Natural Science Foundation of Liaoning Province(20092061 and 20102189)
文摘Dendritic coarsening in AI-2mol%Si alloy during isothermal solidification at 880K was investigated by phase field modeling. Three coarsening mechanisms operate in the alloy： （a） melting of small dendrite arms; （b） coalescence of dendrites near the tips leading to the entrapment of liquid droplets; （c） smoothing of dendrites. Dendrite melting is found to be dominant in the stage of dendritic growth, whereas coalescence of dendrites and smoothing of dendrites are dominant during isothermal holding. The simulated results provide a better understanding of dendrite coarsening during isothermal solidification.
基金Project(20171BAB206005)supported by the Natural Science Foundation of Jiangxi Province,ChinaProject(20153BCB23023)supported by the Training Program Foundation for Young Scientists of Jiangxi Province,ChinaProject(51961026)supported by the National Natural Science Foundation of China。
文摘The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd(x=0,1.5 wt.%,2.0 wt.%and 2.5 wt.%)magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work.Results showed that the lamellar(Mg,Al)3Gd phases transformed into the particle-like Al2Gd phases in AZ31 magnesium alloys with Gd addition during semi-solid isothermal heat treatment,leading to yielding more sphericalα-Mg grains.When Gd content is 2.0 wt.%,the size of semi-solid spherical grains reaches the minimum.The main mechanism of grain refinement lies in the remelting of dendritic branches as well as the auxiliary effect of a small number of Al2Gd particles as grain refining inoculants.Meanwhile,Al2Gd particles enriched at the solid-liquid interfaces can remarkably retard the growth rate ofα-Mg grains.A reduction of deformation resistance has been successfully achieved in AZ31-2.0Gd magnesium alloy after semi-solid isothermal heat treatment,which shows a moderate compressive deformation resistance(230 MPa),comparing to the as-cast AZ31 magnesium alloy(280 MPa)and semi-solid AZ31 magnesium alloy(209 MPa).
文摘In this work, the non-isothermal dissolution kinetics of the sigma phase in duplex stainless steels has been studied and modelled. A semi-empirical model is proposed to describe the kinetics of sigma phase precipitation/dissolution during continuous heating starting from the isothermal transformation kinetics. The proposed model, which presumes validity of the additivity rule, is validated by means of experimental investigations. A good agreement is found between experimental and analytical results.
基金Project(51405216) supported by the National Natural Science Foundation of ChinaProject(20153BCB23023) supported by the Training Programme Foundation for Young Scientists of Jiangxi Province,China
文摘The evolution and distribution of Al2Sm phase in as-extruded AZ61-xSm（x=0, 1.5, 2.0 and 2.5, mass fraction, %） magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0%（mass fraction）, the average size of the globular grains reached the smallest value of 90 μm. Although a few Al2Sm particles existed in the α-Mg grains, most of Al2Sm particles solidified at the edge of the globular grains with the width of 20 μm. These phenomena are mainly attributed to the forces acting on Al2Sm particles in front of the solid-liquid interface, leading to Al2Sm particles accumulating at the solid-liquid interface and then solidifying at the edge of the globular grains in the quenching process.
