The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulati...The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.展开更多
Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosph...Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosphogypsum.However,pipe plugging,which is caused by the poor workability of HPG-based filling materials,has become a major safety hazard in the filling process.Determining an economical and practicable method is urgently needed to improve the workability of HPG slurry work.First,this work found that grind-ing treatment was much more effective than increasing concentration(59wt%-65wt%)and adding tailings(20wt%-100wt%)in enhan-cing the workability of HPG slurry based on a comprehensive analysis of water retention,fluidity,and flow stability.Then,the combined effects of particle size,particle morphology,water film,and interparticle interactions on the workability of HPG slurry were quantitat-ively described through a microanalysis.Moreover,the first direct evidence for the transformation from robust embedded structures to soft stacking structures was presented.In practice,the filling materials should be prepared by grinding HPG for 20 min and mixing with 0-200wt%phosphorus tailings to achieve satisfactory workability and mechanical performance.The results of this study provide practic-al and feasible methods for addressing the stable transportation problem of HPG slurry.展开更多
Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictiv...Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictive relationship between the workability and mechanical properties of UHPFRC. Specifically, the addition of fibers will affect the workability of fresh UHPFRC, and the workability of fresh UHPFRC will also affect the dispersion and arrangement of fibers, thus significantly influencing the mechanical properties of hardened UHPFRC. This paper first analyzes the research status of UHPFRC and the relationship between its workability and mechanical properties. Subsequently, it outlines the test methods and indicators of UHPFRC workability, including fluidity, slump, V-funnel passing time, and rheology. Then, it reviews the impacts of metal fibers, synthetic fibers, hybrid fibers, and other fibers on the workability and mechanical properties of UHPFRC, and presents a reasonable range of fiber dosage for workability and mechanical properties. Key findings include: (1) Steel fibers within 1%–2% volume optimize workability-mechanical balance, while exceeding 2.5% reduces compressive strength by 7%–30%;(2) Hybrid steel-polypropylene fibers enhance toughness by 65%;(3) Fiber orientation control via rheology-modifying admixtures improves flexural strength by up to 64%. This review establishes a fiber factor (V·L/D) for predictive mix design, advancing beyond empirical approaches in prior studies.展开更多
This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox...This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox ratio,and slump flow.The motivation for this study stems from the increasing need to optimize concrete mix designs while minimizing environmental impact and reducing the reliance on costly physical testing.Six ML models-backpropagation neural network(BPNN),random forest regression(RFR),K-nearest neighbors(KNN),stacking,bagging,and eXtreme gradient boosting(XGBoost)-were trained and validated using a comprehensive dataset of 239 mix design parameters.The models'predictive accuracies were assessed using the coefficient of determination,mean squared error,root mean squared error,and mean absolute error.XGBoost consistently outperformed other models,achieving the coefficient of determination values of 0.999,0.933,and 0.935 for compressive strength in the training,validation,and testing datasets,respectively.Sensitivity analysis revealed that cement,silica fume,coarse aggregate,and superplasticizer positively influenced compressive strength,while water content had a negative impact.These findings highlight the potential of ML models,particularly XGBoost and RFR,in optimizing SCC mix designs,reducing reliance on physical testing,and enhancing sustainability in construction.The application of these models can lead to more efficient and eco-friendly concrete mix designs,benefiting real-world construction projects by improving quality control and reducing costs.展开更多
Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability...Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.展开更多
This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution conc...This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution concentrations of 3%,6%,9%,and 12%,the optimal dispersion effect was achieved with an ultrasonic dispersion time of 20 minutes.Specifically,at a 6%nano-TiO_(2)content,both the workability and mechanical performance of the cement paste were enhanced.Furthermore,while nano-TiO_(2)did not alter the types of hydration products present in the cement paste,it did increase the amount of C-S-H gels.This enhancement was attributed to a higher number of nucleation sites for hydration products,which promoted hydration and reduced the porosity of the cement paste.展开更多
The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300...The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.展开更多
The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow inst...The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.展开更多
Flow behaviors of spray forming low solvus high refractory (LSHR) alloy were investigated using hot compression tests performed on a Gleeble?3500 thermal mechanical simulator at temperatures of 1020?1150 °C and s...Flow behaviors of spray forming low solvus high refractory (LSHR) alloy were investigated using hot compression tests performed on a Gleeble?3500 thermal mechanical simulator at temperatures of 1020?1150 °C and strain rates of 0.0003?1.0 s?1. The constitutive equation was established, power dissipation (η) maps and hot processing maps were plotted. The microstructure evolution and dislocation distribution of domains with different values of η in power dissipation maps were also observed. The results show that the flow stress increases with decreasing temperature and increasing strain rate. The activation energy of the spray forming LSHR alloy is 1243.86 kJ/mol. When the value of η is 0.36 at the strain of 0.5, the domain in the processing map shows characteristics of typical dynamic recrystallization (DRX) and low dislocation density. According to the microstructure evolution and processing maps, the optimum processing condition for good hot workability of spray forming LSHR alloy can be summed up as:temperature range 1110?1150 °C; strain rate range 0.01?0.3 s?1.展开更多
The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constituti...The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.展开更多
The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate co...The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate content,with coarse aggregate content of 0%,40%,50%,60%,75%,and 80%,respectively.Slump,compressive and flexural tensile strengths,elastic modulus,and water penetration were tested to research the effect of coarse aggregate content on concrete.The experimental results reveal that slump reduces with increasing of coarse aggregate content,while compressive strength,elastic modulus and flexural tensile strength increase with the coarse aggregate content increasing,and water penetration reduces with coarse aggregate content increasing before 75% then increased.Workability,strength,durability and economical indexes system were established to optimize the coarse aggregate content in concrete based on efficacy coefficient method.The optimization results show that when coarse aggregate content is 60%,the system efficacy coefficient reaches to 0.89,and it expresses the better comprehensive performance.展开更多
This paper investigates the feasibility of using coal gangue as coarse and fine aggregates in concrete as well as how the coal gangue aggregate grading affects concrete properties. Nine mixed concrete samples were pre...This paper investigates the feasibility of using coal gangue as coarse and fine aggregates in concrete as well as how the coal gangue aggregate grading affects concrete properties. Nine mixed concrete samples were prepared with the value n in Fuller＇s curve ranged from 0.44 to 0.68. The coal gangue aggregate with n = 0.62 shows the highest density, water absorption, cylinder strength and the lowest voids. The results indicate that using coal gangue as coarse and fine aggregate in concrete is tech- nically feasible and useful. When n is 0.62, the values of the slump, 28-day compressive, splitting tensile strength, flexural strength and elasticity modulus of coal gangue concrete reach the highest. The highest 7-day and 28-day compressive strength were 24 MPa and 37 MPa in mix CG7, respectively. It is possible to produce grade 30 coal gangue concrete with coal gangue coarse and fine aggregate.展开更多
In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanic...In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.展开更多
High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show t...High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show that the activation energy Q,structure factor a,n and In A varies with the strain,its relationship fit well by fifth order polynomial.The flow stresses predicted by the extracted model are in good agreement with the experimental results.There are five typical domains in the processing map,and the deformation mechanisms in different domains were determined by microstructure analysis.The feasible processing window of the alloy is in the areas of 400-500℃/0.001-0.1 s^(-1).展开更多
The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy ...The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy exhibited a better crack resistance at higher temperature and lower strain rate.Microvoids initiated and coalesced into crack at subsurface on the equatorial plane of bulge surface under secondary tensile condition.The cracks were orientated at an angle of approximately 45° with respect to the compression axis due to the secondary tensile stress.Microcracks easily initiated on the interface of ferrite and austenite and propagated within ferrite.The predicted results using specific plastic work approach were matched well with the free surface cracks.展开更多
The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in t...The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in the temperature range of 250-450 ℃ and strain rate range of 0.001-1.0 s^-1 to establish the processing map. The dynamic recrystallization （DRX） and instability zones were identified and validated through micrographs. The extruded ZE41A magnesium alloy shows higher flow stress, higher efficiency and lower instability regimes than as-cast alloy. The extruded ZE41A magnesium alloy achieves good hot workability due to grain refinement, decrease in porosity, hardening and strengthening of the material.展开更多
The emphasis of this exploration was to examine the workability and work hardening performance of Mg(Magnesium)specimen and Mg-B_(4)C composites created via the powder metallurgy technique.The pure Mg and Mg-B_(4)C co...The emphasis of this exploration was to examine the workability and work hardening performance of Mg(Magnesium)specimen and Mg-B_(4)C composites created via the powder metallurgy technique.The pure Mg and Mg-B_(4)C composites are made with distinct weight percentages(Mg-5%B_(4)C,Mg-10%B_(4)C,and Mg-15%B_(4)C)at the unit aspect ratio.The powders and composites characterization are executed by SEM(Scanning Electron Microscope),EDS(Energy Dispersive Spectrum)with an elemental map,and XRD(X-ray Diffraction)examination.It displays that,the B_(4)C particles were dispersed consistently with the Mg matrix.The workability and work hardening examination was conducted in triaxial stress conditions using the cold deformation process.The consequence of workability stress exponent factor(β_(σ)),distinct stress proportion factors(σ_(m)/σ_(eff)and σ_(θ)/σ_(eff)),instantaneous work hardening exponent(n_(1)),work hardening exponent(n),coefficient of strength(k)and instantaneous coefficient of strength(k_(1))are recognized.The outcome displays that Mg-15%B_(4)C specimen has greater workability and work hardening parameter,initial relative density,and triaxial stresses compared with the Mg specimen and Mg-(5–10%)B_(4)C composites.展开更多
Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most ...Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.展开更多
The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility o...The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility of the steel with Ce addition was increased significantly because of increasing content of austenite,segregation of Ce at grain boundaries and modification of inclusion.The optimum range of Ce content in the steel was 0.030 wt.%-0.047 wt.%,and the optimum value was about 0.047 wt.%.The effect of...展开更多
基金financial support from the National Natural Science Foundation of China(Nos.52233018 and 51831002)the China Baowu Low Carbon Metallurgy Innovation Foudation(No.BWLCF202213)。
文摘The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.
基金financial support from the National Natural Science Foundation of China(No.52074137)the Yunnan Fundamental Research Projects,China(Nos.202301BE070001-054 and 202401CF070124)the Yunnan Major Scientific and Technological Projects,China(No.202403AA080001).
文摘Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosphogypsum.However,pipe plugging,which is caused by the poor workability of HPG-based filling materials,has become a major safety hazard in the filling process.Determining an economical and practicable method is urgently needed to improve the workability of HPG slurry work.First,this work found that grind-ing treatment was much more effective than increasing concentration(59wt%-65wt%)and adding tailings(20wt%-100wt%)in enhan-cing the workability of HPG slurry based on a comprehensive analysis of water retention,fluidity,and flow stability.Then,the combined effects of particle size,particle morphology,water film,and interparticle interactions on the workability of HPG slurry were quantitat-ively described through a microanalysis.Moreover,the first direct evidence for the transformation from robust embedded structures to soft stacking structures was presented.In practice,the filling materials should be prepared by grinding HPG for 20 min and mixing with 0-200wt%phosphorus tailings to achieve satisfactory workability and mechanical performance.The results of this study provide practic-al and feasible methods for addressing the stable transportation problem of HPG slurry.
基金financed by Guangxi Transportation Science and Technology Achievement Promotion Project(GXJT-YFZX-2024-01-01):Intelligent Detection and Data Application R&D Center for Guangxi Transportation Industry.
文摘Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictive relationship between the workability and mechanical properties of UHPFRC. Specifically, the addition of fibers will affect the workability of fresh UHPFRC, and the workability of fresh UHPFRC will also affect the dispersion and arrangement of fibers, thus significantly influencing the mechanical properties of hardened UHPFRC. This paper first analyzes the research status of UHPFRC and the relationship between its workability and mechanical properties. Subsequently, it outlines the test methods and indicators of UHPFRC workability, including fluidity, slump, V-funnel passing time, and rheology. Then, it reviews the impacts of metal fibers, synthetic fibers, hybrid fibers, and other fibers on the workability and mechanical properties of UHPFRC, and presents a reasonable range of fiber dosage for workability and mechanical properties. Key findings include: (1) Steel fibers within 1%–2% volume optimize workability-mechanical balance, while exceeding 2.5% reduces compressive strength by 7%–30%;(2) Hybrid steel-polypropylene fibers enhance toughness by 65%;(3) Fiber orientation control via rheology-modifying admixtures improves flexural strength by up to 64%. This review establishes a fiber factor (V·L/D) for predictive mix design, advancing beyond empirical approaches in prior studies.
文摘This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox ratio,and slump flow.The motivation for this study stems from the increasing need to optimize concrete mix designs while minimizing environmental impact and reducing the reliance on costly physical testing.Six ML models-backpropagation neural network(BPNN),random forest regression(RFR),K-nearest neighbors(KNN),stacking,bagging,and eXtreme gradient boosting(XGBoost)-were trained and validated using a comprehensive dataset of 239 mix design parameters.The models'predictive accuracies were assessed using the coefficient of determination,mean squared error,root mean squared error,and mean absolute error.XGBoost consistently outperformed other models,achieving the coefficient of determination values of 0.999,0.933,and 0.935 for compressive strength in the training,validation,and testing datasets,respectively.Sensitivity analysis revealed that cement,silica fume,coarse aggregate,and superplasticizer positively influenced compressive strength,while water content had a negative impact.These findings highlight the potential of ML models,particularly XGBoost and RFR,in optimizing SCC mix designs,reducing reliance on physical testing,and enhancing sustainability in construction.The application of these models can lead to more efficient and eco-friendly concrete mix designs,benefiting real-world construction projects by improving quality control and reducing costs.
基金supported by the National Natural Science Foundation of China(No.51804232)Beijing Municipal Natural Science Foundation(No.2212041)+1 种基金supported by the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(FRF-IDRY-20-020)GIMRT Program of the Institute for Materials Research,Tohoku University(202303-RDKGE-0518).
文摘Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.
基金Funded by National Natural Science Foundation of China(No.52108188)State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)(No.SYSJJ2024-15)+3 种基金State Key Laboratory of Mountain Bridge and Tunnel Engineering,Chongqing Jiaotong University(No.SKLBT-2301)Opening Project of State Key Laboratory of Green Building Materials(No.2022GBM10)Open Research Fund of Key Laboratory of Engineering Materials of Ministry of Water Resources,China Institute of Water Resources and Hydropower Research(No.EMF202407)General Project of Science and Technology Plan of Beijing Municipal Commission of Education(No.KM202110005018)。
文摘This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution concentrations of 3%,6%,9%,and 12%,the optimal dispersion effect was achieved with an ultrasonic dispersion time of 20 minutes.Specifically,at a 6%nano-TiO_(2)content,both the workability and mechanical performance of the cement paste were enhanced.Furthermore,while nano-TiO_(2)did not alter the types of hydration products present in the cement paste,it did increase the amount of C-S-H gels.This enhancement was attributed to a higher number of nucleation sites for hydration products,which promoted hydration and reduced the porosity of the cement paste.
基金Projects(2010CB731701,2012CB619502) supported by the National Basic Research Program of ChinaProject(CX2012B043) supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProject(51021063) supported by Creative Research Group of National Natural Science Foundation of China
文摘The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.
基金Project(2011ZX04014-051)supported by the Key Scientific and Technical Project of ChinaProjects(51375306,50905110)supported by the National Natural Science Foundation of China
文摘The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.
基金Project(51301143)supported by the National Natural Science Foundation of ChinaProject(2014M560727)supported by the National Postdoctoral Foundation of China+1 种基金Project(2015GZ0228)supported by the Sichuan Province Science-Technology Support Plan,ChinaProject(2682014CX001)supported by the Science and Technology Innovation Project of SWJTU University,China
文摘Flow behaviors of spray forming low solvus high refractory (LSHR) alloy were investigated using hot compression tests performed on a Gleeble?3500 thermal mechanical simulator at temperatures of 1020?1150 °C and strain rates of 0.0003?1.0 s?1. The constitutive equation was established, power dissipation (η) maps and hot processing maps were plotted. The microstructure evolution and dislocation distribution of domains with different values of η in power dissipation maps were also observed. The results show that the flow stress increases with decreasing temperature and increasing strain rate. The activation energy of the spray forming LSHR alloy is 1243.86 kJ/mol. When the value of η is 0.36 at the strain of 0.5, the domain in the processing map shows characteristics of typical dynamic recrystallization (DRX) and low dislocation density. According to the microstructure evolution and processing maps, the optimum processing condition for good hot workability of spray forming LSHR alloy can be summed up as:temperature range 1110?1150 °C; strain rate range 0.01?0.3 s?1.
基金Projects(51171113,51301107) supported by the National Natural Science Foundation of China
文摘The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.
基金Funded by the National Mega-project of Scientific & Technical Supporting Programs,Ministry of Science & Technology of China(No.2006BAJ04A04)the Education Department of Liaoning Province,China(No. 2008282)
文摘The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate content,with coarse aggregate content of 0%,40%,50%,60%,75%,and 80%,respectively.Slump,compressive and flexural tensile strengths,elastic modulus,and water penetration were tested to research the effect of coarse aggregate content on concrete.The experimental results reveal that slump reduces with increasing of coarse aggregate content,while compressive strength,elastic modulus and flexural tensile strength increase with the coarse aggregate content increasing,and water penetration reduces with coarse aggregate content increasing before 75% then increased.Workability,strength,durability and economical indexes system were established to optimize the coarse aggregate content in concrete based on efficacy coefficient method.The optimization results show that when coarse aggregate content is 60%,the system efficacy coefficient reaches to 0.89,and it expresses the better comprehensive performance.
基金Supported by the National Natural Science Foundation of China(U126112,11226250)China Postdoctoral Science Foundation(2013M541236)
文摘This paper investigates the feasibility of using coal gangue as coarse and fine aggregates in concrete as well as how the coal gangue aggregate grading affects concrete properties. Nine mixed concrete samples were prepared with the value n in Fuller＇s curve ranged from 0.44 to 0.68. The coal gangue aggregate with n = 0.62 shows the highest density, water absorption, cylinder strength and the lowest voids. The results indicate that using coal gangue as coarse and fine aggregate in concrete is tech- nically feasible and useful. When n is 0.62, the values of the slump, 28-day compressive, splitting tensile strength, flexural strength and elasticity modulus of coal gangue concrete reach the highest. The highest 7-day and 28-day compressive strength were 24 MPa and 37 MPa in mix CG7, respectively. It is possible to produce grade 30 coal gangue concrete with coal gangue coarse and fine aggregate.
文摘In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.
基金the National Natural Science Foundation of China(Grant no.51501015).
文摘High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show that the activation energy Q,structure factor a,n and In A varies with the strain,its relationship fit well by fifth order polynomial.The flow stresses predicted by the extracted model are in good agreement with the experimental results.There are five typical domains in the processing map,and the deformation mechanisms in different domains were determined by microstructure analysis.The feasible processing window of the alloy is in the areas of 400-500℃/0.001-0.1 s^(-1).
基金Item Sponsored by National Natrural Science Foundation of China(50734002)
文摘The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy exhibited a better crack resistance at higher temperature and lower strain rate.Microvoids initiated and coalesced into crack at subsurface on the equatorial plane of bulge surface under secondary tensile condition.The cracks were orientated at an angle of approximately 45° with respect to the compression axis due to the secondary tensile stress.Microcracks easily initiated on the interface of ferrite and austenite and propagated within ferrite.The predicted results using specific plastic work approach were matched well with the free surface cracks.
文摘The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in the temperature range of 250-450 ℃ and strain rate range of 0.001-1.0 s^-1 to establish the processing map. The dynamic recrystallization （DRX） and instability zones were identified and validated through micrographs. The extruded ZE41A magnesium alloy shows higher flow stress, higher efficiency and lower instability regimes than as-cast alloy. The extruded ZE41A magnesium alloy achieves good hot workability due to grain refinement, decrease in porosity, hardening and strengthening of the material.
文摘The emphasis of this exploration was to examine the workability and work hardening performance of Mg(Magnesium)specimen and Mg-B_(4)C composites created via the powder metallurgy technique.The pure Mg and Mg-B_(4)C composites are made with distinct weight percentages(Mg-5%B_(4)C,Mg-10%B_(4)C,and Mg-15%B_(4)C)at the unit aspect ratio.The powders and composites characterization are executed by SEM(Scanning Electron Microscope),EDS(Energy Dispersive Spectrum)with an elemental map,and XRD(X-ray Diffraction)examination.It displays that,the B_(4)C particles were dispersed consistently with the Mg matrix.The workability and work hardening examination was conducted in triaxial stress conditions using the cold deformation process.The consequence of workability stress exponent factor(β_(σ)),distinct stress proportion factors(σ_(m)/σ_(eff)and σ_(θ)/σ_(eff)),instantaneous work hardening exponent(n_(1)),work hardening exponent(n),coefficient of strength(k)and instantaneous coefficient of strength(k_(1))are recognized.The outcome displays that Mg-15%B_(4)C specimen has greater workability and work hardening parameter,initial relative density,and triaxial stresses compared with the Mg specimen and Mg-(5–10%)B_(4)C composites.
基金support from the National Natural Science Foundation of China, No.50771011
文摘Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.
文摘The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility of the steel with Ce addition was increased significantly because of increasing content of austenite,segregation of Ce at grain boundaries and modification of inclusion.The optimum range of Ce content in the steel was 0.030 wt.%-0.047 wt.%,and the optimum value was about 0.047 wt.%.The effect of...
