In response to the urgent demand for lightweight,magnesium(Mg)alloys have garnered considerable attention owing to their low density.Nonetheless,the intrinsic poor room-temperature formability of Mg alloys remains a m...In response to the urgent demand for lightweight,magnesium(Mg)alloys have garnered considerable attention owing to their low density.Nonetheless,the intrinsic poor room-temperature formability of Mg alloys remains a major obstacle in shaping precise complex components,necessitating the development of superplastic Mg alloys.Excellent superplasticity is usually acquired in high-alloyed Mg alloys with enhanced microstructural thermal stability facilitated by abundant optimized second-phase particles.While for cost-effective low-alloyed Mg alloys lacking particles,regulating solute segregation has emerged as a promising approach to achieve superplasticity recently.Moreover,the potential of bimodal-grained Mg alloys for superplastic deformation has been revealed,expanding the options for designing superplastic materials beyond the conventional approach of fine-grained microstructures.This study reviews significant developments in superplastic Mg alloys from the view of alloying strategies,grain structure control and deformation mechanisms,with potential implications for future research and industrial applications of superplastic Mg alloys.展开更多
Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at dif...Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at different strain rates and temperatures,and an optimal superplastic elongation of 634%was achieved at 700℃ and 3×10^(-4)/s.An annealing treatment at 650℃ for 60 min showed a mi-crostructure withαprecipitates distributed in theβmatrix in the friction stir specimen.Such pre-heat treatment improves the superplasticity of the specimen,achieving an elongation of up to 807%at 750℃ and 3×10^(-4)/s.The influences of tensile temperatures and strain rates on the microstructural evolution,such as grain size variation,grain morphology,and phase transformations,were discussed.The super-plastic deformation behavior of fine-grained Ti-10V-2Fe-3Al alloy is controlled by grain boundary sliding and accompanied by dynamic phase transformation and recrystallization.展开更多
The mechanochemical synthesis of polycarboxylate superplasticizers(PCEs)was achieved using a planetary ball mill at ambient temperature.The effects of ball milling parameters,including speed,time,and stop method,on PC...The mechanochemical synthesis of polycarboxylate superplasticizers(PCEs)was achieved using a planetary ball mill at ambient temperature.The effects of ball milling parameters,including speed,time,and stop method,on PCE performance,molecular weight,and distribution were investigated to optimize conditions.The experimental results suggest that ball milling impacts PCE molecular weight and distribution,striking a balance between polymerization and mechanical degradation during synthesis.The optimal parameters were found to be 400 rpm,120 minutes total time,and 30 minutes milling plus 3 minutes rest cycles.Under these conditions,the PCE exhibits excellent dispersibility with a cement paste fluidity of 260 mm.The mechanochemical approach eliminates heating requirements,and also reduces the reaction time from 300 to 120 minutes compared to traditional aqueous synthesis.The optimized PCE demonstrates an increased density of long-side chains,leading to enhanced early strength,heightens adsorption,and diminished zeta potential in cement systems.These characteristics are comparable to traditionally synthesized PCEs.Moreover,at higher dosages,further augmentation of PCE adsorption and increased cement paste fluidity were noted here.展开更多
For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,...For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,an ultrafine bimodal microstructure,consisting of ultrafine equiaxed microstructure(0.66μm)and 43.3%lamellar microstructure,was achieved in the Ti-6Al-4V alloy by friction stir processing(FSP).The low-temperature superplastic behavior and deformation mechanism of the FSP Ti-6Al-4V alloy were investigated at temperatures of 550-675℃and strain rates ranging from 1×10^(−4)to 3×10^(−3)s^(−1).The FSP alloy exhibited superplastic elongations of>200%at the temperature range from 550 to 650℃,and an optimal superplastic elongation of 611%was achieved at 625℃and 1×10^(−4)s^(−1).This is the first time to report the low-temperature superplasticity of the bimodal microstructure in Ti alloys.Grain boundary sliding was identified as the dominant deformation mechanism,which was effectively accommodated by the comprehensive effect of dislocation-inducedβphase precipitation and dynamic spheroidization of the lamellar structure.This study provides a novel insight into the low-temperature superplastic deformation behavior of the bimodal microstructure.展开更多
This article presents a preparation method for a tailing sand-specific polycarboxylate superplasticizer(AT9)containing multifunctional adsorption groups.By designing multifunctional adsorption groups(-COOH)as side cha...This article presents a preparation method for a tailing sand-specific polycarboxylate superplasticizer(AT9)containing multifunctional adsorption groups.By designing multifunctional adsorption groups(-COOH)as side chains grafted onto the main chain of conventional polycarboxylate ether,the antiadsorption effect is achieved.AT9 was characterized by gel permeation chromatography,and its performance was systematically evaluated in various tailings sand-cement mortar systems.A comparison was made between AT9 and traditional PCE in terms of their effects on the workability of concrete,and the interaction mechanism between AT9 and clay in cementitious systems was discussed.The results indicate that AT9 enhances the adsorption and dispersion effects of polycarboxylate superplasticizers on cement particles,and increases steric hindrance,thereby avoids intercalation adsorption of tailings sand,improves its water-reducing and slump-retaining performance,and also contributes to the strength enhancement of concrete in later stages.展开更多
The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate t...The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.展开更多
Aluminium alloy is one of the earliest and most widely used superplastic materials.The objective of this work is to review the scientific advances in superplastic Al alloys.Particularly,the emphasis is placed on the m...Aluminium alloy is one of the earliest and most widely used superplastic materials.The objective of this work is to review the scientific advances in superplastic Al alloys.Particularly,the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation.The evolution of grain structure,texture,secondary phase,and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail.The quantitative evaluation of different deformation mechanisms based on the focus ion beam(FIB)-assisted surface study provides new insights into the superplasticity of Al alloys.The main features,such as grain boundary sliding,intragranular dislocation slip,and diffusion creep can be observed intuitively and analyzed quantitatively.This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.展开更多
The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαph...The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαphase,were examined in a temperature range of 473 K to 623 K.The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling.The best superplasticity was achieved at 523 K and at strain rates of 10^(-4)-5×10^(-4)s^(-1),where tensile elongations of 550±600%were obtained.During the heating and holding stage of the tensile samples prior to tensile loading,a significant increase in grain size was observed at temperatures above 573 K.Therefore,it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms.In the investigated strain rate range,the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding,while at high strain rates,lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism.It was concluded that solute drag creep is unlikely to occur.During the late stages of deformation at 523 K,it was observed that grain boundary sliding led to the agglomeration of theαphase,resulting in significant strain hardening.Deformation mechanism maps were constructed forβ-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate,stress,temperature,and grain size,using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.展开更多
The aim of this work is to predict,for the first time,the high temperature flow stress dependency with the grain size and the underlaid deformation mechanism using two machine learning models,random forest(RF)and arti...The aim of this work is to predict,for the first time,the high temperature flow stress dependency with the grain size and the underlaid deformation mechanism using two machine learning models,random forest(RF)and artificial neural network(ANN).With that purpose,a ZK30 magnesium alloy was friction stir processed(FSP)using three different severe conditions to obtain fine grain microstructures(with average grain sizes between 2 and 3μm)prone to extensive superplastic response.The three friction stir processed samples clearly deformed by grain boundary sliding(GBS)deformation mechanism at high temperatures.The maximum elongations to failure,well over 400% at high strain rate of 10^(-2)s^(-1),were reached at 400℃ in the material with coarsest grain size of 2.8μm,and at 300℃ for the finest grain size of 2μm.Nevertheless,the superplastic response decreased at 350℃ and 400℃ due to thermal instabilities and grain coarsening,which makes it difficult to assess the operative deformation mechanism at such temperatures.This work highlights that the machine learning models considered,especially the ANN model with higher accuracy in predicting flow stress values,allow determining adequately the superplastic creep behavior including other possible grain size scenarios.展开更多
Achieving impressive superplasticity is an important strategy to manufacture Mg alloy products with complex shapes.In the present study,we report that an excellent superplastic deformation with elongation larger than ...Achieving impressive superplasticity is an important strategy to manufacture Mg alloy products with complex shapes.In the present study,we report that an excellent superplastic deformation with elongation larger than 500%can be achieved at 623 K and 1.0×10^(−3)s^(−1)in a Mg-1.51Zn-0.59Ca-0.59Al-0.70Mn(wt.%,ZXAM2111)alloy fabricated by equal-channel angular pressing.The superplastic deformation is mainly carried by grain boundary sliding(GBS),accompanied by a grain size growth from∼3.0μm to∼6.0μm after deformation.Before deformation,the ZXAM2111 alloy is mainly characterized by a strong co-segregation of Zn and Ca atoms at grain boundaries and uniformly distributedβ-Mn particles.With deformation proceeding,theβ-Mn particles further dynamically precipitate along grain boundaries that parallel the tensile axis,leading to improved resistance to grain coarsening.Although the enhanced stabilizing effects decrease the strain rate sensitivity value,the resulting impressive microstructure stability provides a cornerstone of the active operation of GBS,facilitating the achievement of superplastic deformation.The present work could provide insight into developing low-alloyed Mg alloys with high microstructure thermal stability to achieve superplasticity.展开更多
Superplastic forming is a practical method to manufacture complex-shaped parts of titanium alloys with large deformation.Laminated parts of dissimilar titanium alloys fabricated by superplastic forming can achieve exc...Superplastic forming is a practical method to manufacture complex-shaped parts of titanium alloys with large deformation.Laminated parts of dissimilar titanium alloys fabricated by superplastic forming can achieve excellent performance by combining the advantages of components.This work displays the superplastic tension behavior and microstructural evolution of dissimilar TC4/SP700 laminate prepared by the diffusion bonding process.Two titanium alloys can achieve metallurgical bonding at parameters of 800℃/1 h/5 MPa.Except for dynamic recrystallization and grain growth behaviors upon superplastic tension,stress-induced phase transformation plays an important role inαtoβphase transformation apart from the elevated temperature.The superplastic deformation can be attributed to the grain boundary sliding accommodated multiplex motion of dislocations.In addition,the retained strengths of all dissimilar TC4/SP700 laminates after superplastic deformation with different strain rates and temperatures range from 807 to 890 MPa.展开更多
The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity....The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity.It was observed that the dissolution ofγ′-particles resulted in the creation of vacancies due to differences in atomic size between the matrix and the particles.These vacancies acted as inclusions,leading to the formation of micro-voids.Notably,excessive void formation correlated with higher particle dissolution was experimentally observed,highlighting a direct relationship between void formation and particle dissolution.展开更多
The global awareness and utilization of superplasticizers (SPs) in concrete have significantly contributed to developing resilient and sustainable infrastructure. Despite this, many developing nations face limited ado...The global awareness and utilization of superplasticizers (SPs) in concrete have significantly contributed to developing resilient and sustainable infrastructure. Despite this, many developing nations face limited adoption of SPs in construction practices due to a lack of knowledge. This study provides a concise overview of concrete’s mechanical and durability properties, comparing formulations with and without superplasticizers. The focus is on compressive and flexural strengths, modulus of elasticity, water sorptivity, and chloride penetration. The results underscore the considerable improvement in both mechanical and durability properties when SPs are incorporated. The study recommends the widespread use of SPs, particularly in developing countries, to enhance the longevity of concrete structures.展开更多
This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow e...This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.展开更多
Microstructure and tensile behaviors of AZ31 magnesium alloy prepared by friction stir processing（FSP） were investigated.The results show that microstructure of the AZ31 hot-rolled plate with an average grain size o...Microstructure and tensile behaviors of AZ31 magnesium alloy prepared by friction stir processing（FSP） were investigated.The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 92.0 μm is refined to 11.4 μm after FSP.The FSP AZ31 alloy exhibits excellent plasticity at elevated temperature,with an elongation to failure of 1050% at 723 K and a strain rate of 5×10-4 s-1.The elongation of the FSP material is 268% at 723 K and 1×10-2 s-1,indicating that high strain rate superplasticity could be achieved.On the other hand,the hot-rolled base material,which has a coarse grain structure,possesses no superplasticity under the experimental conditions.展开更多
The microstructural evolution of banded 5A90 A1-Li alloy during superplastic deformation at 475℃ with an initial strain rate of 8× 10^-4 S^-1 was studied using EBSD technique. The results showed that, before def...The microstructural evolution of banded 5A90 A1-Li alloy during superplastic deformation at 475℃ with an initial strain rate of 8× 10^-4 S^-1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of { 110}（112） brass texture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding （GBS）. At large strains, GBS was the main mechanism.展开更多
A novel thermomechanical processing was developed for producing fine grained Al-Mg-Li alloy sheets. The influences of static recrystallization annealing on the grain structure and superplastic behavior were investigat...A novel thermomechanical processing was developed for producing fine grained Al-Mg-Li alloy sheets. The influences of static recrystallization annealing on the grain structure and superplastic behavior were investigated. The results show that the refined microstructure has a variation in the distribution of grain size, shape and texture across the normal direction of the sheet. The surface layer （SL） has fine, nearly equiaxed grains with a rotated cUbeND {001 }（310） orientation, whereas the center layer （CL） has coarse, elongated grains with a portion of a fiber orientation. Increasing static recrystallized temperature results in grain growth in the full thickness, decreasing of grain aspect ratio in the center layer, texture sharpening in the surface layer, but weakening in the center layer as well as decreasing of superplastic elongation. Increasing the annealing temperature also produces an sharpening of the rotated cube {001}（310） component and a decreasing of the a fiber texture in the full thickness of the sheet. The formation mechanisms of recrystallization texture at various temperatures and layers were discussed.展开更多
Microstructure and texture evolution during high-strain-rate superplastic deformation of the rolled Mg-Gd-Y-Zr sheet were investigated.The tensile tests at the strain rate of 0.01 s-1 achieved the elongations of 180%-...Microstructure and texture evolution during high-strain-rate superplastic deformation of the rolled Mg-Gd-Y-Zr sheet were investigated.The tensile tests at the strain rate of 0.01 s-1 achieved the elongations of 180%-266% in the deformation temperature range of 400-500 ℃.Post-deforming microstructures were characterized by optical microscopy,scanning electron microscopy and transmission electron microscopy,while crystallographic orientation information was obtained from macro-texture analysis.The results show that the high strain-rate superplasticity was attributed to class-I dislocation creep accommodated by dynamic recrystallization （DRX）.During preheating at 435 ℃ for 600 s,twinning-induced recrystallization occurred.The initial strain of 80% made original grains fragmented and produced homogenous DRX grains.The interaction between dynamic recrystallization and dynamic precipitation yielded out such a phenomenon that finer DRX grains were often accompanied by denser particles.The macro-texture evolution exhibited some characteristics of the crystal rotation arising from basal slip and prismatic slip despite the occurrence of DRX.展开更多
In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer a...In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer are selected to investigate the influence of superplasticizers on the early-age cracking resistance of the concrete by using the slab test and the temperature-stress test. The results show that the polycarboxlic salt/acid superplasticizer cannot always improve the cracking resistance capacity of the concrete compared with the naphthalene superplasticizer, which is related to the chemical structure of the polycarboxlic salt/acid superplasticizer. High plastic tensile strength and dynamic elastic modulus at the early stage are beneficial to avoid cracking, and low hydration heat is also helpful. The evolutions of the drying shrilakage stress and the hydration heat temperature stress varying with time can be comprehensively evaluated by means of the slab test and the temperature stress test.展开更多
An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process ...An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters.Formability was assessed using elevated temperature tensile testing and hot gas bulging,across a range of strain rates(1×10^(−1)−1×10^(−3)s^(−1))and temperatures(350−450℃).Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes.Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability,with dynamic recrystallization being clearly evident.Peak elongation of 520%was achieved at 450℃ and 1×10^(−3)s^(−1);industrially relevant elongation was achieved at 1×10^(−2) s^(−1) at both 450℃(195%)and 400℃(170%).展开更多
基金primarily supported by The National Natural Science Foundation of China(under Nos.52234009 and 52271103)Partial financial support came from the Program for the Central University Youth Innovation Team(No.419021423505)the Fundamental Research Funds for the Central Universities,JLU.
文摘In response to the urgent demand for lightweight,magnesium(Mg)alloys have garnered considerable attention owing to their low density.Nonetheless,the intrinsic poor room-temperature formability of Mg alloys remains a major obstacle in shaping precise complex components,necessitating the development of superplastic Mg alloys.Excellent superplasticity is usually acquired in high-alloyed Mg alloys with enhanced microstructural thermal stability facilitated by abundant optimized second-phase particles.While for cost-effective low-alloyed Mg alloys lacking particles,regulating solute segregation has emerged as a promising approach to achieve superplasticity recently.Moreover,the potential of bimodal-grained Mg alloys for superplastic deformation has been revealed,expanding the options for designing superplastic materials beyond the conventional approach of fine-grained microstructures.This study reviews significant developments in superplastic Mg alloys from the view of alloying strategies,grain structure control and deformation mechanisms,with potential implications for future research and industrial applications of superplastic Mg alloys.
基金financially supported by the National Natural Science Foundation of China(No.52105373)the China Scholarship Council(No.202106020094).
文摘Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at different strain rates and temperatures,and an optimal superplastic elongation of 634%was achieved at 700℃ and 3×10^(-4)/s.An annealing treatment at 650℃ for 60 min showed a mi-crostructure withαprecipitates distributed in theβmatrix in the friction stir specimen.Such pre-heat treatment improves the superplasticity of the specimen,achieving an elongation of up to 807%at 750℃ and 3×10^(-4)/s.The influences of tensile temperatures and strain rates on the microstructural evolution,such as grain size variation,grain morphology,and phase transformations,were discussed.The super-plastic deformation behavior of fine-grained Ti-10V-2Fe-3Al alloy is controlled by grain boundary sliding and accompanied by dynamic phase transformation and recrystallization.
基金Funded by the National Natural Science Foundation of China(Nos.U1905216 and 52108208)the Henan Provincial Science and Technology Research Project(No.212102310559)。
文摘The mechanochemical synthesis of polycarboxylate superplasticizers(PCEs)was achieved using a planetary ball mill at ambient temperature.The effects of ball milling parameters,including speed,time,and stop method,on PCE performance,molecular weight,and distribution were investigated to optimize conditions.The experimental results suggest that ball milling impacts PCE molecular weight and distribution,striking a balance between polymerization and mechanical degradation during synthesis.The optimal parameters were found to be 400 rpm,120 minutes total time,and 30 minutes milling plus 3 minutes rest cycles.Under these conditions,the PCE exhibits excellent dispersibility with a cement paste fluidity of 260 mm.The mechanochemical approach eliminates heating requirements,and also reduces the reaction time from 300 to 120 minutes compared to traditional aqueous synthesis.The optimized PCE demonstrates an increased density of long-side chains,leading to enhanced early strength,heightens adsorption,and diminished zeta potential in cement systems.These characteristics are comparable to traditionally synthesized PCEs.Moreover,at higher dosages,further augmentation of PCE adsorption and increased cement paste fluidity were noted here.
基金supported by the funding from the Shi Changxu Innovation Center for Advanced Materials(No.SCXKFJJ202210)the National Natural Science Foundation of China(No.52271043)+2 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021193)the Liaoning Province Excellent Youth Foundation(No.2024JH3/10200021)the Liaoning Revitalization Talents Program(No.XLYC2403094).
文摘For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,an ultrafine bimodal microstructure,consisting of ultrafine equiaxed microstructure(0.66μm)and 43.3%lamellar microstructure,was achieved in the Ti-6Al-4V alloy by friction stir processing(FSP).The low-temperature superplastic behavior and deformation mechanism of the FSP Ti-6Al-4V alloy were investigated at temperatures of 550-675℃and strain rates ranging from 1×10^(−4)to 3×10^(−3)s^(−1).The FSP alloy exhibited superplastic elongations of>200%at the temperature range from 550 to 650℃,and an optimal superplastic elongation of 611%was achieved at 625℃and 1×10^(−4)s^(−1).This is the first time to report the low-temperature superplasticity of the bimodal microstructure in Ti alloys.Grain boundary sliding was identified as the dominant deformation mechanism,which was effectively accommodated by the comprehensive effect of dislocation-inducedβphase precipitation and dynamic spheroidization of the lamellar structure.This study provides a novel insight into the low-temperature superplastic deformation behavior of the bimodal microstructure.
文摘This article presents a preparation method for a tailing sand-specific polycarboxylate superplasticizer(AT9)containing multifunctional adsorption groups.By designing multifunctional adsorption groups(-COOH)as side chains grafted onto the main chain of conventional polycarboxylate ether,the antiadsorption effect is achieved.AT9 was characterized by gel permeation chromatography,and its performance was systematically evaluated in various tailings sand-cement mortar systems.A comparison was made between AT9 and traditional PCE in terms of their effects on the workability of concrete,and the interaction mechanism between AT9 and clay in cementitious systems was discussed.The results indicate that AT9 enhances the adsorption and dispersion effects of polycarboxylate superplasticizers on cement particles,and increases steric hindrance,thereby avoids intercalation adsorption of tailings sand,improves its water-reducing and slump-retaining performance,and also contributes to the strength enhancement of concrete in later stages.
基金supported by the National Natural Science Foundation of China(No.52127808)。
文摘The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.
文摘Aluminium alloy is one of the earliest and most widely used superplastic materials.The objective of this work is to review the scientific advances in superplastic Al alloys.Particularly,the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation.The evolution of grain structure,texture,secondary phase,and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail.The quantitative evaluation of different deformation mechanisms based on the focus ion beam(FIB)-assisted surface study provides new insights into the superplasticity of Al alloys.The main features,such as grain boundary sliding,intragranular dislocation slip,and diffusion creep can be observed intuitively and analyzed quantitatively.This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.
文摘The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαphase,were examined in a temperature range of 473 K to 623 K.The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling.The best superplasticity was achieved at 523 K and at strain rates of 10^(-4)-5×10^(-4)s^(-1),where tensile elongations of 550±600%were obtained.During the heating and holding stage of the tensile samples prior to tensile loading,a significant increase in grain size was observed at temperatures above 573 K.Therefore,it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms.In the investigated strain rate range,the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding,while at high strain rates,lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism.It was concluded that solute drag creep is unlikely to occur.During the late stages of deformation at 523 K,it was observed that grain boundary sliding led to the agglomeration of theαphase,resulting in significant strain hardening.Deformation mechanism maps were constructed forβ-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate,stress,temperature,and grain size,using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.
基金obtained from Comunidad de Madrid through the Universidad Politécnica de Madrid in the line of Action for Encouraging Research from Young Doctors(project CdM ref:APOYO-JOVENES779NQU-57-LSWH0F,UPM ref M190020074AOC,CAREDEL)MINECO(Spain)Project MAT2015-68919-C3-1-R(MINECO/FEDER)+4 种基金project PID2020-118626RB-I00(RAPIDAL)awarded by MCIN/AEI/10.13039/501100011033FSP assistanceProject CAREDELProject RAPIDAL for research contractsMCIN/AEI for a FPI contract number PRE2021-096977。
文摘The aim of this work is to predict,for the first time,the high temperature flow stress dependency with the grain size and the underlaid deformation mechanism using two machine learning models,random forest(RF)and artificial neural network(ANN).With that purpose,a ZK30 magnesium alloy was friction stir processed(FSP)using three different severe conditions to obtain fine grain microstructures(with average grain sizes between 2 and 3μm)prone to extensive superplastic response.The three friction stir processed samples clearly deformed by grain boundary sliding(GBS)deformation mechanism at high temperatures.The maximum elongations to failure,well over 400% at high strain rate of 10^(-2)s^(-1),were reached at 400℃ in the material with coarsest grain size of 2.8μm,and at 300℃ for the finest grain size of 2μm.Nevertheless,the superplastic response decreased at 350℃ and 400℃ due to thermal instabilities and grain coarsening,which makes it difficult to assess the operative deformation mechanism at such temperatures.This work highlights that the machine learning models considered,especially the ANN model with higher accuracy in predicting flow stress values,allow determining adequately the superplastic creep behavior including other possible grain size scenarios.
基金Financial supports from The National Natural Science Foundation of China(Nos.U19A2084,52171116 and 52074132)are greatly acknowledgedPartial financial support came from The Science and Technology Development Program of Jilin Province(Nos.20200201002JC and 20200401025GX).
文摘Achieving impressive superplasticity is an important strategy to manufacture Mg alloy products with complex shapes.In the present study,we report that an excellent superplastic deformation with elongation larger than 500%can be achieved at 623 K and 1.0×10^(−3)s^(−1)in a Mg-1.51Zn-0.59Ca-0.59Al-0.70Mn(wt.%,ZXAM2111)alloy fabricated by equal-channel angular pressing.The superplastic deformation is mainly carried by grain boundary sliding(GBS),accompanied by a grain size growth from∼3.0μm to∼6.0μm after deformation.Before deformation,the ZXAM2111 alloy is mainly characterized by a strong co-segregation of Zn and Ca atoms at grain boundaries and uniformly distributedβ-Mn particles.With deformation proceeding,theβ-Mn particles further dynamically precipitate along grain boundaries that parallel the tensile axis,leading to improved resistance to grain coarsening.Although the enhanced stabilizing effects decrease the strain rate sensitivity value,the resulting impressive microstructure stability provides a cornerstone of the active operation of GBS,facilitating the achievement of superplastic deformation.The present work could provide insight into developing low-alloyed Mg alloys with high microstructure thermal stability to achieve superplasticity.
基金The authors gratefully appreciate financial support by the National Natural Science Foundation of China(No.51875350).
文摘Superplastic forming is a practical method to manufacture complex-shaped parts of titanium alloys with large deformation.Laminated parts of dissimilar titanium alloys fabricated by superplastic forming can achieve excellent performance by combining the advantages of components.This work displays the superplastic tension behavior and microstructural evolution of dissimilar TC4/SP700 laminate prepared by the diffusion bonding process.Two titanium alloys can achieve metallurgical bonding at parameters of 800℃/1 h/5 MPa.Except for dynamic recrystallization and grain growth behaviors upon superplastic tension,stress-induced phase transformation plays an important role inαtoβphase transformation apart from the elevated temperature.The superplastic deformation can be attributed to the grain boundary sliding accommodated multiplex motion of dislocations.In addition,the retained strengths of all dissimilar TC4/SP700 laminates after superplastic deformation with different strain rates and temperatures range from 807 to 890 MPa.
基金financial support from the National Key R&D Program of China(2019YFA0705300)the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024).
文摘The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity.It was observed that the dissolution ofγ′-particles resulted in the creation of vacancies due to differences in atomic size between the matrix and the particles.These vacancies acted as inclusions,leading to the formation of micro-voids.Notably,excessive void formation correlated with higher particle dissolution was experimentally observed,highlighting a direct relationship between void formation and particle dissolution.
文摘The global awareness and utilization of superplasticizers (SPs) in concrete have significantly contributed to developing resilient and sustainable infrastructure. Despite this, many developing nations face limited adoption of SPs in construction practices due to a lack of knowledge. This study provides a concise overview of concrete’s mechanical and durability properties, comparing formulations with and without superplasticizers. The focus is on compressive and flexural strengths, modulus of elasticity, water sorptivity, and chloride penetration. The results underscore the considerable improvement in both mechanical and durability properties when SPs are incorporated. The study recommends the widespread use of SPs, particularly in developing countries, to enhance the longevity of concrete structures.
文摘This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.
基金Project (2009Z2-D811) supported by Guangzhou Science and Technology Development Program, ChinaProject (2009ZM0264) supported by the Fundamental Research Funds for the Central Universities, China
文摘Microstructure and tensile behaviors of AZ31 magnesium alloy prepared by friction stir processing（FSP） were investigated.The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 92.0 μm is refined to 11.4 μm after FSP.The FSP AZ31 alloy exhibits excellent plasticity at elevated temperature,with an elongation to failure of 1050% at 723 K and a strain rate of 5×10-4 s-1.The elongation of the FSP material is 268% at 723 K and 1×10-2 s-1,indicating that high strain rate superplasticity could be achieved.On the other hand,the hot-rolled base material,which has a coarse grain structure,possesses no superplasticity under the experimental conditions.
基金Project(51205419)supported by the National Natural Science Foundation of China
文摘The microstructural evolution of banded 5A90 A1-Li alloy during superplastic deformation at 475℃ with an initial strain rate of 8× 10^-4 S^-1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of { 110}（112） brass texture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding （GBS）. At large strains, GBS was the main mechanism.
基金Project(51205419)supported by the National Natural Science Foundation of China
文摘A novel thermomechanical processing was developed for producing fine grained Al-Mg-Li alloy sheets. The influences of static recrystallization annealing on the grain structure and superplastic behavior were investigated. The results show that the refined microstructure has a variation in the distribution of grain size, shape and texture across the normal direction of the sheet. The surface layer （SL） has fine, nearly equiaxed grains with a rotated cUbeND {001 }（310） orientation, whereas the center layer （CL） has coarse, elongated grains with a portion of a fiber orientation. Increasing static recrystallized temperature results in grain growth in the full thickness, decreasing of grain aspect ratio in the center layer, texture sharpening in the surface layer, but weakening in the center layer as well as decreasing of superplastic elongation. Increasing the annealing temperature also produces an sharpening of the rotated cube {001}（310） component and a decreasing of the a fiber texture in the full thickness of the sheet. The formation mechanisms of recrystallization texture at various temperatures and layers were discussed.
基金Project supported by Natural Science Foundation of Hunan Province,China
文摘Microstructure and texture evolution during high-strain-rate superplastic deformation of the rolled Mg-Gd-Y-Zr sheet were investigated.The tensile tests at the strain rate of 0.01 s-1 achieved the elongations of 180%-266% in the deformation temperature range of 400-500 ℃.Post-deforming microstructures were characterized by optical microscopy,scanning electron microscopy and transmission electron microscopy,while crystallographic orientation information was obtained from macro-texture analysis.The results show that the high strain-rate superplasticity was attributed to class-I dislocation creep accommodated by dynamic recrystallization （DRX）.During preheating at 435 ℃ for 600 s,twinning-induced recrystallization occurred.The initial strain of 80% made original grains fragmented and produced homogenous DRX grains.The interaction between dynamic recrystallization and dynamic precipitation yielded out such a phenomenon that finer DRX grains were often accompanied by denser particles.The macro-texture evolution exhibited some characteristics of the crystal rotation arising from basal slip and prismatic slip despite the occurrence of DRX.
基金International Collaborative Research Project of Sika Technology AG of Switzerland,the Traffic Scientific Research Project in Jiangsu Province (No. 2010Y01)
文摘In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer are selected to investigate the influence of superplasticizers on the early-age cracking resistance of the concrete by using the slab test and the temperature-stress test. The results show that the polycarboxlic salt/acid superplasticizer cannot always improve the cracking resistance capacity of the concrete compared with the naphthalene superplasticizer, which is related to the chemical structure of the polycarboxlic salt/acid superplasticizer. High plastic tensile strength and dynamic elastic modulus at the early stage are beneficial to avoid cracking, and low hydration heat is also helpful. The evolutions of the drying shrilakage stress and the hydration heat temperature stress varying with time can be comprehensively evaluated by means of the slab test and the temperature stress test.
基金The authors would like to thank the WMG High Value Manufacturing Catapult Centre for funding this work.In addition,the characterisation facility is supported from the Higher Education Funding Council for England(HEFCE).
文摘An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters.Formability was assessed using elevated temperature tensile testing and hot gas bulging,across a range of strain rates(1×10^(−1)−1×10^(−3)s^(−1))and temperatures(350−450℃).Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes.Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability,with dynamic recrystallization being clearly evident.Peak elongation of 520%was achieved at 450℃ and 1×10^(−3)s^(−1);industrially relevant elongation was achieved at 1×10^(−2) s^(−1) at both 450℃(195%)and 400℃(170%).
