Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.T...Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.The microstructure of as-cast Ti-5552-xNb alloy is consisted of a singleβphase,and theβgrain size increases slightly with the increase of Nb content.The thermal effect in the process of high temperature drawing leads to the precipitation ofαphase.The addition of Nb in Ti-5552 titanium alloys reduces theα/βphase transformation temperature,which causes a decrease in the volume fraction ofαphase.Reducing theαphase content reduces incompatibility,but too low a proportion ofαphase will lead to premature fracture,so tensile strength and plasticity firstly increase and then decrease.The results show that Ti-5552-9Nb titanium alloy shows the best tensile strength(307.2 MPa)and superplasticity(106%).The superplastic mechanism of Ti-5552-9Nb alloy is mainly caused by relative sliding ofβgrain boundaries and dislocation movement.展开更多
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 Mg-4Y-3RE(WE43)magnesium alloy possesses significant advantages such as high specific strength,excellent shock absorption,strong electromagnetic shielding capabilities and recyclability.However,its close-packed he...The Mg-4Y-3RE(WE43)magnesium alloy possesses significant advantages such as high specific strength,excellent shock absorption,strong electromagnetic shielding capabilities and recyclability.However,its close-packed hexagonal structure leads to poor plasticity at room temperature,which limits its broader engineering applications.Therefore,superplastic forming at high temperatures is used to manufacture the components from this alloy.This study conducted tensile tests on hot-rolled WE43 rare-earth magnesium alloy with coarse grains at various temperatures and strain rates.The high-temperature superplastic properties were characterized,revealing the intrinsic mechanisms of thermal deformation behavior.The results indicate that the best superplasticity is achieved at 460℃.This is attributed to the smallest grain size,the weakest texture,and the relatively uniform distribution of the second phase at this temperature.The influence of strain rate on elongation at temperatures among 440℃∼500℃is not significant as the impact of strain rate is multifaceted.Meanwhile,the elongation can reach up to 367.7±3.7%at a strain rate of 0.01s^(−1),which exhibits the high strain rate superplasticity(HSRS).Under these conditions,the deformation of coarse-grained WE43 rare-earth magnesium alloy is controlled by grain boundary sliding(GBS)and solute drag dislocation creep.Furthermore,the GBS involves deformation coordination mechanisms such as grain boundary diffusion,lattice diffusion,dislocation climbing,and dynamic recrystallization accommodation mechanisms.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
The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongati...The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongation exceeding 230%in a coarse-grained Ni-Co-based superalloy.The deformed microstructure and fractographic characteristics of the alloy were examined utilizing optical microscopy(OM),scanning electron microscopy(SEM),and electron backscatter diffraction(EBSD).The results of the analysis revealed that below 1100℃,the process of dynamic recrystallization(DRX)occurred at a sluggish rate,resulting in low plasticity and the initiation of severe cracks.Complete DRX occurred when the deformation temperature exceeded 1100℃,leading to a more uniformly deformed microstructure,reduced crack initiation,and enhanced ductility demonstrated by elongation to failure surpassing 230%.The augmented occurrence of the DRX facilitated prolonged plastic-forming periods,which delayed fracture propagation and promoted the deformation flow within the alloy,thereby transitioning the fracture behavior from intergranular-brittle at 1050℃to ductile intergranular at 1140℃.At this temperature,the deformation was predominantly governed by the discontinuous-DRX(DDRX)mechanism and grain growth,facilitated by the formation of twin boundaries.展开更多
A new type of extruded nickel-based powder metallurgy(P/M)superalloy was subjected to isothermal compression and tensile experiments to explore its superplasticity.Based on the compression flow curves,the hot working ...A new type of extruded nickel-based powder metallurgy(P/M)superalloy was subjected to isothermal compression and tensile experiments to explore its superplasticity.Based on the compression flow curves,the hot working maps of strain rate sensitivity index(m)were established at various strain levels.When compressing at1020-1110℃,in the strain rate range of 0.001-0.01 s^(-1),the m value was always greater than 0.3,indicating that the superalloy exhibited superplasticity in this deformation region.The tensile results showed that the superalloy exhibited excellent superplasticity under the conditions of 1050℃/0.01 s^(-1),1080℃/0.01 s^(-1)and 1110℃/0.001 s^(-1),with elongation after fracture reaching up to 1011%,1038%and951%,respectively.At low-temperature conditions and hightemperature/low strain rate conditions,both continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)were activated.As the deformation temperature increased,theγphases gradually dissolved into the matrix,and the primaryγ'phase changed from irregular shape to spherical or near-spherical shape.The interaction of theγ'phase with the dislocation promoted dynamic recrystallization(DRX)nucleation and thus slowed down the grain growth rate,which was essential for the superplastic deformation of the alloy.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
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
Tensile behaviors of an AZS0 alloy were investigated by elongation-to-failure tensile tests at 300, 350, 400 and 450 ℃, and strain rates of 10-2 and 10-3 s 1. Strain-rate-change tests from 5×10-5 s-1 to 2x10-2 s...Tensile behaviors of an AZS0 alloy were investigated by elongation-to-failure tensile tests at 300, 350, 400 and 450 ℃, and strain rates of 10-2 and 10-3 s 1. Strain-rate-change tests from 5×10-5 s-1 to 2x10-2 s-1 were applied to study deformation mechanisms. The experimental data show that the material exhibits enhanced tensile ductilities of over 100% at 400 and 450 ℃ with stress exponent of 4.29 and activation energy of 149.60 kJ/mol, and initial fine grains preserve in evenly deformed gauge based on microstructure studies. The enhanced tensile ductilities are rate controlled by a competitive mechanism of grain boundary sliding and dislocation climb creep, based on which a model can successfully simulate the deformation behavior.展开更多
Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup&g...Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup> to 5.21×10<sup>-1</sup> s<sup>-1</sup>. The maximum total elongation of 228 % is obtained at a strain rate of 2.08×10<sup>-1</sup> s<sup>-1</sup>. The strain rate se nsitivity exponent （m） higher than 0.3, is observed when the strain rate is high er than 10<sup>-1</sup> s<sup>-1</sup> at 525℃. Increasing the test temperature to 540℃, the maximum total elongation exceeding 195% is achieved at a higher strain rate of 5.21×10<sup>-1</sup> s<sup>-1</sup> than that at 525℃. SiC in AZ31/SiCp composite ca n fine the matrix grain size. Filament is observed on the fracture surface of th e specimens showing superplasticity.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
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
In order to analyze and simulate the complex super-plastic forming process by computer, a method of equal height bulging for determining material parameters m and K of the superplastic alloy is presented. The formulae...In order to analyze and simulate the complex super-plastic forming process by computer, a method of equal height bulging for determining material parameters m and K of the superplastic alloy is presented. The formulae related to the method are deduced in this paper. The accuracy of the method is available for evaluating the examples used in simulating the superplastic sheet-metal bulging processes.展开更多
The method is recently developed to obtain the optimum superplastic property of Ti_3Al alloys. Mode is established, and after the calculation to analyze the present model the parameters is found fit to the curve expre...The method is recently developed to obtain the optimum superplastic property of Ti_3Al alloys. Mode is established, and after the calculation to analyze the present model the parameters is found fit to the curve expressing the high plastic well here. m>K>n is the found turn in these three parameters which causes the super-plasticity effectively, this effect may be studied further to demonstrate it to be effective definitely.展开更多
Hot compression tests of the extruded 7075Al/15%SiC (volume fraction) particle reinforced composite prepared by spray deposition were performed on Gleeble?1500 system in the temperature range of 300?450 °C and st...Hot compression tests of the extruded 7075Al/15%SiC (volume fraction) particle reinforced composite prepared by spray deposition were performed on Gleeble?1500 system in the temperature range of 300?450 °C and strain rate range of 0.001?1 s?1. The results indicate that the true stress?true strain curve almost exhibits rapid flow softening phenomenon without an obvious work hardening, and the stress decreases with increasing temperature and decreasing strain rate. Moreover, the stress levels are higher at temperature below 400 °C but lower at 450 °C compared with the spray deposited 7075Al alloy. Superplastic deformation characteristics are found at temperature of 450 °C and strain rate range of 0.001?0.1 s?1 with corresponding strain rate sensitivity of 0.72. The optimum parameters of hot working are determined to be temperature of 430?450 °C and strain rate of 0.001?0.05 s?1 based on processing map and optical microstructural observation.展开更多
Magnesium(Mg)alloys have been extensively used in various fields,such as aerospace,automobile,electronics,and biomedical industries,due to their high specific strength and stiff ness,excellent vibration absorption,ele...Magnesium(Mg)alloys have been extensively used in various fields,such as aerospace,automobile,electronics,and biomedical industries,due to their high specific strength and stiff ness,excellent vibration absorption,electromagnetic shielding eff ect,good machinability,and recyclability.Friction stir processing(FSP)is a severe plastic deformation technique,based on the principle of friction stir welding.In addition to introducing the basic principle and advantages of FSP,this paper reviews the studies of FSP in the modification of the cast structure,superplastic deformation behavior,preparation of finegrained Mg alloys and Mg-based surface composites,and additive manufacturing.FSP not only refines,homogenizes,and densifies the microstructure,but also eliminates the cast microstructure defects,breaks up the brittle and network-like phases,and prepares fine-grained,ultrafine-,and nano-grained Mg alloys.Indeed,FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity.Furthermore,FSP can produce particle-and fiber-reinforced Mg-based surface composites.As a promising additive manufacturing technique of light metals,FSP enables the additive manufacturing of Mg alloys.Finally,we prospect the future research direction and application with friction stir processed Mg alloys.展开更多
The magnesium alloys are the next-generation lightweight metal materials;however, the production of the complex shape components of thermo-mechanical processed magnesium alloys is very limited in comparison to their d...The magnesium alloys are the next-generation lightweight metal materials;however, the production of the complex shape components of thermo-mechanical processed magnesium alloys is very limited in comparison to their die-casted counterparts. Both high strain rate and low-temperature processing are required to save time and cost for the project. Uniaxial tensile testing has been vastly used for determining the plasticity of magnesium alloys at elevated temperatures. Therefore, this review article sheds light on superplastic behaviors under the uniaxial tensile loading of different magnesium alloys. This review also emphasizes low and high-temperature superplasticity, high strain rate superplasticity, deformation mechanism, thermal stability, texture evaluation, and fracture mechanism of extruded/rolled and severe plastic deformed magnesium alloys. At the end of the review, some technical issues have been addressed which can be beneficial for further enhancement in the superplasticity of magnesium alloys.展开更多
基金the financial support by the Major Science and Technology Achievement Transformation Project in Heilongjiang Province(ZC2023SH0075)the National Natural Science Foundation of China(52425401,U2441255,52474377,and 52371015)+1 种基金the Young Elite Scientists Sponsorship Program by·CAST(2021QNRC001)the Henan Provincial Key Research and Development&Promotion Special Program(251111231400)。
文摘Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.The microstructure of as-cast Ti-5552-xNb alloy is consisted of a singleβphase,and theβgrain size increases slightly with the increase of Nb content.The thermal effect in the process of high temperature drawing leads to the precipitation ofαphase.The addition of Nb in Ti-5552 titanium alloys reduces theα/βphase transformation temperature,which causes a decrease in the volume fraction ofαphase.Reducing theαphase content reduces incompatibility,but too low a proportion ofαphase will lead to premature fracture,so tensile strength and plasticity firstly increase and then decrease.The results show that Ti-5552-9Nb titanium alloy shows the best tensile strength(307.2 MPa)and superplasticity(106%).The superplastic mechanism of Ti-5552-9Nb alloy is mainly caused by relative sliding ofβgrain boundaries and dislocation movement.
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The authors gratefully appreciate financial support by Program of Shanghai Academic Research Leader(No.22XD1421600).
文摘The Mg-4Y-3RE(WE43)magnesium alloy possesses significant advantages such as high specific strength,excellent shock absorption,strong electromagnetic shielding capabilities and recyclability.However,its close-packed hexagonal structure leads to poor plasticity at room temperature,which limits its broader engineering applications.Therefore,superplastic forming at high temperatures is used to manufacture the components from this alloy.This study conducted tensile tests on hot-rolled WE43 rare-earth magnesium alloy with coarse grains at various temperatures and strain rates.The high-temperature superplastic properties were characterized,revealing the intrinsic mechanisms of thermal deformation behavior.The results indicate that the best superplasticity is achieved at 460℃.This is attributed to the smallest grain size,the weakest texture,and the relatively uniform distribution of the second phase at this temperature.The influence of strain rate on elongation at temperatures among 440℃∼500℃is not significant as the impact of strain rate is multifaceted.Meanwhile,the elongation can reach up to 367.7±3.7%at a strain rate of 0.01s^(−1),which exhibits the high strain rate superplasticity(HSRS).Under these conditions,the deformation of coarse-grained WE43 rare-earth magnesium alloy is controlled by grain boundary sliding(GBS)and solute drag dislocation creep.Furthermore,the GBS involves deformation coordination mechanisms such as grain boundary diffusion,lattice diffusion,dislocation climbing,and dynamic recrystallization accommodation mechanisms.
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.
基金financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC0140000)the National Science and Technology Major Project(No.J2019-VI-0006-0120)+3 种基金the Science and Technology Major Project of Liaoning Province(No.2024JH1/11700037)the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024)the National Science and Technology Major Project(No.2024ZD0600600).
文摘The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongation exceeding 230%in a coarse-grained Ni-Co-based superalloy.The deformed microstructure and fractographic characteristics of the alloy were examined utilizing optical microscopy(OM),scanning electron microscopy(SEM),and electron backscatter diffraction(EBSD).The results of the analysis revealed that below 1100℃,the process of dynamic recrystallization(DRX)occurred at a sluggish rate,resulting in low plasticity and the initiation of severe cracks.Complete DRX occurred when the deformation temperature exceeded 1100℃,leading to a more uniformly deformed microstructure,reduced crack initiation,and enhanced ductility demonstrated by elongation to failure surpassing 230%.The augmented occurrence of the DRX facilitated prolonged plastic-forming periods,which delayed fracture propagation and promoted the deformation flow within the alloy,thereby transitioning the fracture behavior from intergranular-brittle at 1050℃to ductile intergranular at 1140℃.At this temperature,the deformation was predominantly governed by the discontinuous-DRX(DDRX)mechanism and grain growth,facilitated by the formation of twin boundaries.
基金financially supported by Shandong Provincial Natural Science Foundation of China(Nos.ZR2024JQ020 and ZR2021QE102)Taishan Scholars Program of Shandong Province(Nos.tsqn202211115 and tsqn202306162)+2 种基金Yantai high-end talent introduction"Double Hundred Plan"(2021)the Science Foundation Program for Distinguished Young Scholars of Shandong(Overseas)(No.2022HWYQ-084)the Talent Training Program for Shandong Province Higher Educational Youth Innovative Teams(2021)
文摘A new type of extruded nickel-based powder metallurgy(P/M)superalloy was subjected to isothermal compression and tensile experiments to explore its superplasticity.Based on the compression flow curves,the hot working maps of strain rate sensitivity index(m)were established at various strain levels.When compressing at1020-1110℃,in the strain rate range of 0.001-0.01 s^(-1),the m value was always greater than 0.3,indicating that the superalloy exhibited superplasticity in this deformation region.The tensile results showed that the superalloy exhibited excellent superplasticity under the conditions of 1050℃/0.01 s^(-1),1080℃/0.01 s^(-1)and 1110℃/0.001 s^(-1),with elongation after fracture reaching up to 1011%,1038%and951%,respectively.At low-temperature conditions and hightemperature/low strain rate conditions,both continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)were activated.As the deformation temperature increased,theγphases gradually dissolved into the matrix,and the primaryγ'phase changed from irregular shape to spherical or near-spherical shape.The interaction of theγ'phase with the dislocation promoted dynamic recrystallization(DRX)nucleation and thus slowed down the grain growth rate,which was essential for the superplastic deformation of the alloy.
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.
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(50801034)supported by the National Natural Science Foundation of ChinaProject(LJQ 2011026)supported by Development Foundation for Excellent Young Scholars in Universities of Liaoning Province,ChinaProject(2006207)supported by Foundation for "Ten-Hundred-Thousand" High-end Talent Introduction Project in Liaoning Province,China
文摘Tensile behaviors of an AZS0 alloy were investigated by elongation-to-failure tensile tests at 300, 350, 400 and 450 ℃, and strain rates of 10-2 and 10-3 s 1. Strain-rate-change tests from 5×10-5 s-1 to 2x10-2 s-1 were applied to study deformation mechanisms. The experimental data show that the material exhibits enhanced tensile ductilities of over 100% at 400 and 450 ℃ with stress exponent of 4.29 and activation energy of 149.60 kJ/mol, and initial fine grains preserve in evenly deformed gauge based on microstructure studies. The enhanced tensile ductilities are rate controlled by a competitive mechanism of grain boundary sliding and dislocation climb creep, based on which a model can successfully simulate the deformation behavior.
文摘Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10<sup>-3</sup> to 5.21×10<sup>-1</sup> s<sup>-1</sup>. The maximum total elongation of 228 % is obtained at a strain rate of 2.08×10<sup>-1</sup> s<sup>-1</sup>. The strain rate se nsitivity exponent （m） higher than 0.3, is observed when the strain rate is high er than 10<sup>-1</sup> s<sup>-1</sup> at 525℃. Increasing the test temperature to 540℃, the maximum total elongation exceeding 195% is achieved at a higher strain rate of 5.21×10<sup>-1</sup> s<sup>-1</sup> than that at 525℃. SiC in AZ31/SiCp composite ca n fine the matrix grain size. Filament is observed on the fracture surface of th e specimens showing superplasticity.
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.
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.
文摘In order to analyze and simulate the complex super-plastic forming process by computer, a method of equal height bulging for determining material parameters m and K of the superplastic alloy is presented. The formulae related to the method are deduced in this paper. The accuracy of the method is available for evaluating the examples used in simulating the superplastic sheet-metal bulging processes.
基金supported by the Korea of Science and Engineering Fund(96-0300-11-01-3)
文摘The method is recently developed to obtain the optimum superplastic property of Ti_3Al alloys. Mode is established, and after the calculation to analyze the present model the parameters is found fit to the curve expressing the high plastic well here. m>K>n is the found turn in these three parameters which causes the super-plasticity effectively, this effect may be studied further to demonstrate it to be effective definitely.
基金Project(51271076)supported by the National Natural Science Foundation of China
文摘Hot compression tests of the extruded 7075Al/15%SiC (volume fraction) particle reinforced composite prepared by spray deposition were performed on Gleeble?1500 system in the temperature range of 300?450 °C and strain rate range of 0.001?1 s?1. The results indicate that the true stress?true strain curve almost exhibits rapid flow softening phenomenon without an obvious work hardening, and the stress decreases with increasing temperature and decreasing strain rate. Moreover, the stress levels are higher at temperature below 400 °C but lower at 450 °C compared with the spray deposited 7075Al alloy. Superplastic deformation characteristics are found at temperature of 450 °C and strain rate range of 0.001?0.1 s?1 with corresponding strain rate sensitivity of 0.72. The optimum parameters of hot working are determined to be temperature of 430?450 °C and strain rate of 0.001?0.05 s?1 based on processing map and optical microstructural observation.
基金sponsorship from the National Natural Science Foundation of China(Nos.51574192,51404180,51974220,and U1760201)the Key Industrial Research Program of Shaanxi Province,China(No.2017ZDXMGY-037)+1 种基金the National Key Research and Development Program of China(No.Z20180407)the Youth Innovation Team of Shaanxi Universities(No.2019-2022).
文摘Magnesium(Mg)alloys have been extensively used in various fields,such as aerospace,automobile,electronics,and biomedical industries,due to their high specific strength and stiff ness,excellent vibration absorption,electromagnetic shielding eff ect,good machinability,and recyclability.Friction stir processing(FSP)is a severe plastic deformation technique,based on the principle of friction stir welding.In addition to introducing the basic principle and advantages of FSP,this paper reviews the studies of FSP in the modification of the cast structure,superplastic deformation behavior,preparation of finegrained Mg alloys and Mg-based surface composites,and additive manufacturing.FSP not only refines,homogenizes,and densifies the microstructure,but also eliminates the cast microstructure defects,breaks up the brittle and network-like phases,and prepares fine-grained,ultrafine-,and nano-grained Mg alloys.Indeed,FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity.Furthermore,FSP can produce particle-and fiber-reinforced Mg-based surface composites.As a promising additive manufacturing technique of light metals,FSP enables the additive manufacturing of Mg alloys.Finally,we prospect the future research direction and application with friction stir processed Mg alloys.
基金the National Natural Science Foundation of China(52005103,71801046,51775112)the Guangdong Basic and Applied Basic Research Foundation(2019B1515120095)+1 种基金the Intelligent Manufacturing PHM Innovation Team Program(2018KCXTD029,TDYB2019010)the Key Project of the CSTC(2019jcyj-zdxm X0013)。
文摘The magnesium alloys are the next-generation lightweight metal materials;however, the production of the complex shape components of thermo-mechanical processed magnesium alloys is very limited in comparison to their die-casted counterparts. Both high strain rate and low-temperature processing are required to save time and cost for the project. Uniaxial tensile testing has been vastly used for determining the plasticity of magnesium alloys at elevated temperatures. Therefore, this review article sheds light on superplastic behaviors under the uniaxial tensile loading of different magnesium alloys. This review also emphasizes low and high-temperature superplasticity, high strain rate superplasticity, deformation mechanism, thermal stability, texture evaluation, and fracture mechanism of extruded/rolled and severe plastic deformed magnesium alloys. At the end of the review, some technical issues have been addressed which can be beneficial for further enhancement in the superplasticity of magnesium alloys.
