The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300...The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.展开更多
The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in t...The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in the temperature range of 250-450 ℃ and strain rate range of 0.001-1.0 s^-1 to establish the processing map. The dynamic recrystallization （DRX） and instability zones were identified and validated through micrographs. The extruded ZE41A magnesium alloy shows higher flow stress, higher efficiency and lower instability regimes than as-cast alloy. The extruded ZE41A magnesium alloy achieves good hot workability due to grain refinement, decrease in porosity, hardening and strengthening of the material.展开更多
The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility o...The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility of the steel with Ce addition was increased significantly because of increasing content of austenite,segregation of Ce at grain boundaries and modification of inclusion.The optimum range of Ce content in the steel was 0.030 wt.%-0.047 wt.%,and the optimum value was about 0.047 wt.%.The effect of...展开更多
Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot co...Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing,numerical modeling and microstructural analyses.Hot deformation tests are performed at temperatures of 250℃ to 400℃ under strain rates of 0.01 to 1.0 s^(−1).Transmission electron microscopy is used to reveal the presence of dynamic recrystallization(DRX),dynamic recovery(DRY),cracks and shear bands.To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy,the authors use Johnson–Cook damage model in a 3D finite element simulation.The optimal hot workability of magnesium alloy is found at a temperature(T)of 400℃ and strain rate(ε)of 0.01 s^(−1).Stability is found at a lower strain rate,and instability is found at a higher strain rate.展开更多
Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging...Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.展开更多
Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain...Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.展开更多
The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was develop...The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was developed and its reliability was verified.Its hot processing map was constructed,and combined with microstructural observations,a semi-quantitative response relationship between hot deformation parameters and microstructure was established.The DRX process of N6 is a thermally activated process and particularly sensitive to the strain rate.The optimal hot processing parameters for N6 were determined to be 950−1050℃ and 0.1−1 s^(−1).Furthermore,it was proven that the dominant nucleation mechanism is discontinuous DRX characterized by grain boundary bulging and twins assisting nucleation,while the continuous DRX characterized by subgrains combined with rotation is an inactive nucleation mechanism.展开更多
Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always...Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always been an important topic in the field of titanium alloy processing.This paper proposed a strategy of adding Mo and Fe elements to simultaneously reduce the hot working temperature and high-temperature deformation resistance of Ti-6Al-4V alloy.The effects of Mo and Fe contents on the mi-crostructure,β transus temperature(Tp),and high-temperature flow stress(HFS)of Ti-6Al-4V-xMo-xFe(x=0-5)alloys were investigated.The results showed that adding Mo and Fe can substantially reduce the Tp and HFS of the alloy,and greatly improve its room-temperature strength.Compared with com-mercial Ti-6Al-4V samples,the T_(β) of Ti-6Al-4V-2Mo-2Fe and Ti-6Al-4V-3Mo-3Fe samples was decreased by 68-98 ℃,and the HFS at 800-900 ℃ was decreased by 37.8%-46.0%.Compared with hot-rolled Ti-6Al-4V samples,the room-temperature tensile strength of hot-rolled Ti-6Al-4V-2Mo-2Fe samples was increased by about 30%,while the elongation hardly decreased.The increased strength was mainly at-tributed to fine grain strengthening and solid solution strengthening.The hot workability and room-temperature strength of Ti-6Al-4V alloy can be significantly improved by adding 2-3 wt.%Mo and Fe simultaneously.展开更多
Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy wer...Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism, microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization （DRX） contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 ℃, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature （below 350 ℃）, the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 ℃ and 1 s^-1.展开更多
Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability...Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.展开更多
The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulati...The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.展开更多
The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy ...The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy exhibited a better crack resistance at higher temperature and lower strain rate.Microvoids initiated and coalesced into crack at subsurface on the equatorial plane of bulge surface under secondary tensile condition.The cracks were orientated at an angle of approximately 45° with respect to the compression axis due to the secondary tensile stress.Microcracks easily initiated on the interface of ferrite and austenite and propagated within ferrite.The predicted results using specific plastic work approach were matched well with the free surface cracks.展开更多
Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true ...Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true stress-strain curves of the steel were characterized by hardening and subsequent softening and varied with temperatures and strain rates. The hot deformation activation energy of the steel was calculated to be 657.4 k J/mol, which was higher than that of the corresponding wrought steel due to its as-cast coarse columnar grains and heterogeneous structure. Hot processing maps were developed at different plastic strains, which exhibited two domains with peak power dissipation efficiencies at 1150 ℃/0.001 s^（-1） and 1200 ℃/1 s^（-1）, respectively. The corresponding microstructures were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, and electron backscatter diffraction（EBSD）. It has been confirmed that dynamic recrystallization（DRX） controlled by dislocation slipping and climbing mechanism occurs in the temperature and strain rate range of 1050-1200 ℃ and 0.001-0.01 s^（-1）; And DRX controlled by twinning mechanism occurs in the temperature and strain rate range of 1100-1200 ℃, 0.1-1 s^（-1）. These two DRX domains can serve as the hot working windows of the as-cast steel at lower strain rates and at higher strain rates, respectively. The processing maps at different strains also exhibit that the instability region decreases with increasing strain. The corresponding microstructures and the less tensile ductility in the instability region imply that the flow instability is attributed to flow localization accelerated by a few layers of very fine recrystallized grains along the original grain boundaries.展开更多
The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on...The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on the hot deformation behavior of medium carbon steel was determined.The hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator deformed at temperatures from 850 to 1 200 ℃ and strain rates from 0.001 to 1 s^-1.The processing maps of two test steels were built at a true strain of 0.7 based on dynamic materials model（DMM）.There are two peak efficiency domains and two flow instability regions in both test steels.However,the peak efficiency domains of Nb-bearing steel move to higher temperature due to the inhibition of dynamic recrystaUization（DRX）,and the instability domains of Nb-bearing steel are enlarged due to the precipitation of Nb-containing particles during hot deformation.The optimum process parameters of Nb-bearing and Nb-free steels for industrial production were determined according to the processing map and the microstructural observation.展开更多
Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most ...Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.展开更多
The deformation flow behaviors of Ti-45Al-5.4V-3.6Nb-0.3Y alloy at different temperatures and strain rates were studied by isothermal compressing simulation test.The apparent activation energy of deformation was calcu...The deformation flow behaviors of Ti-45Al-5.4V-3.6Nb-0.3Y alloy at different temperatures and strain rates were studied by isothermal compressing simulation test.The apparent activation energy of deformation was calculated to be 402.096 kJ/mol and constitutive equation was established to describe the flow behavior.Microstructure and flow softening observations exhibited that Ti-45Al-5.4V3.6Nb-0.3Y alloy had bad hot workability at low temperature （lower than 1 100 oC） and high strain rate （higher than 0.5 s–1） characterized by localization deformation and instability.With deformation temperature higher than 1 150 oC and strain rate lower than 0.01 s–1,the alloy owned good hot deformability,and plenty of dynamic recrystallized grains could be observed in the deformed microstructures.展开更多
Titanium has been widely used as the implant materials of joint prostheses. This paper simulates the microstructures of the hot forged titanium knee joint component by physical modeling. Ti-6Al-4V ELI were deformed b...Titanium has been widely used as the implant materials of joint prostheses. This paper simulates the microstructures of the hot forged titanium knee joint component by physical modeling. Ti-6Al-4V ELI were deformed by GLEEBLE 2000 hot deforma- tion simulator in compression mode to determine the hot workability, in the range of 900 to 1100℃, with the strain rates between 0.05 to 5 s^(-1). Test results derived from specimens processed by on-cooling test and on-heating test were compared, thereby estimating the effect due to thermal history. The forging process of Ti-6Al-4V ELI tibial base plate of knee joint prostheses was design based on the workability data obtained.展开更多
TiAl base alloys have potential usage in aerospace engine for their high specific strength. In order to improve their poor hot workability, a new approach of hot deformation processing was investigated. The starting m...TiAl base alloys have potential usage in aerospace engine for their high specific strength. In order to improve their poor hot workability, a new approach of hot deformation processing was investigated. The starting microstructure of Ti 46 5Al 2 5V 1 0Cr (atom percent, %) alloy is fully lamellar (FL) microstructure. The near gamma (NG) microstructure can be obtained through Nickel microalloying and heat treatment at 1 150 ℃. The isothermal compression tests were conducted on both materials using MTS machine at temperatures of 950 ℃, 1 000 ℃, and 1 050 ℃, and the strain rates of 0 01, 0 1 and 1 s -1 . Compared with the γ TiAl alloy with FL microstructure, the Ni bearing alloy with NG microstructure has better hot workability, such as enlarged hot workable region, decreased flow stresses, more uniform and finer deformed microstructure.展开更多
基金Projects(2010CB731701,2012CB619502) supported by the National Basic Research Program of ChinaProject(CX2012B043) supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProject(51021063) supported by Creative Research Group of National Natural Science Foundation of China
文摘The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.
文摘The hot deformation behavior and microstructure evolution of as-cast and extruded ZE41A magnesium alloy were studied using processing maps. The compression tests were conducted on both as-cast and extruded alloys in the temperature range of 250-450 ℃ and strain rate range of 0.001-1.0 s^-1 to establish the processing map. The dynamic recrystallization （DRX） and instability zones were identified and validated through micrographs. The extruded ZE41A magnesium alloy shows higher flow stress, higher efficiency and lower instability regimes than as-cast alloy. The extruded ZE41A magnesium alloy achieves good hot workability due to grain refinement, decrease in porosity, hardening and strengthening of the material.
文摘The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy(SEM).The results showed that ductility of the steel with Ce addition was increased significantly because of increasing content of austenite,segregation of Ce at grain boundaries and modification of inclusion.The optimum range of Ce content in the steel was 0.030 wt.%-0.047 wt.%,and the optimum value was about 0.047 wt.%.The effect of...
文摘Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing,numerical modeling and microstructural analyses.Hot deformation tests are performed at temperatures of 250℃ to 400℃ under strain rates of 0.01 to 1.0 s^(−1).Transmission electron microscopy is used to reveal the presence of dynamic recrystallization(DRX),dynamic recovery(DRY),cracks and shear bands.To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy,the authors use Johnson–Cook damage model in a 3D finite element simulation.The optimal hot workability of magnesium alloy is found at a temperature(T)of 400℃ and strain rate(ε)of 0.01 s^(−1).Stability is found at a lower strain rate,and instability is found at a higher strain rate.
基金National Natural Science Foundation of China(No.52305373)Jiangxi Provincial Natural Science Foundation(No.20232BAB214053)+2 种基金Science and Technology Major Project of Jiangxi,China(No.20194ABC28001)Fund of Jiangxi Key Laboratory of Forming and Joining Technology for Aerospace Components,Nanchang Hangkong University(No.EL202303299)PhD Starting Foundation of Nanchang Hangkong University(No,EA202303235).
文摘Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.
基金supported by the National Natural Science Foundation of China(51774124,52074114)Hunan Provincial Natural Science Foundation of China(2019JJ40017,2020JJ5062)+1 种基金Key Technologies R&D in Strategic Emerging Industries and Transformation in High-tech Achievements Program of Hunan Province(2019GK4045)Graduate Training and Innovation Practice Base of Hunan Province.
文摘Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.
基金supported by the Science Foundation for Distinguished Young Scholars of Gansu Province,China(No.18JR3RA134)Lanzhou University of Technology Support Plan for Excellent Young Scholars,China(No.CGZH001)the National Nature Science Foundation of China(No.51665032).
文摘The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was developed and its reliability was verified.Its hot processing map was constructed,and combined with microstructural observations,a semi-quantitative response relationship between hot deformation parameters and microstructure was established.The DRX process of N6 is a thermally activated process and particularly sensitive to the strain rate.The optimal hot processing parameters for N6 were determined to be 950−1050℃ and 0.1−1 s^(−1).Furthermore,it was proven that the dominant nucleation mechanism is discontinuous DRX characterized by grain boundary bulging and twins assisting nucleation,while the continuous DRX characterized by subgrains combined with rotation is an inactive nucleation mechanism.
基金National Natural Science Foundation of China(No.52090041).
文摘Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always been an important topic in the field of titanium alloy processing.This paper proposed a strategy of adding Mo and Fe elements to simultaneously reduce the hot working temperature and high-temperature deformation resistance of Ti-6Al-4V alloy.The effects of Mo and Fe contents on the mi-crostructure,β transus temperature(Tp),and high-temperature flow stress(HFS)of Ti-6Al-4V-xMo-xFe(x=0-5)alloys were investigated.The results showed that adding Mo and Fe can substantially reduce the Tp and HFS of the alloy,and greatly improve its room-temperature strength.Compared with com-mercial Ti-6Al-4V samples,the T_(β) of Ti-6Al-4V-2Mo-2Fe and Ti-6Al-4V-3Mo-3Fe samples was decreased by 68-98 ℃,and the HFS at 800-900 ℃ was decreased by 37.8%-46.0%.Compared with hot-rolled Ti-6Al-4V samples,the room-temperature tensile strength of hot-rolled Ti-6Al-4V-2Mo-2Fe samples was increased by about 30%,while the elongation hardly decreased.The increased strength was mainly at-tributed to fine grain strengthening and solid solution strengthening.The hot workability and room-temperature strength of Ti-6Al-4V alloy can be significantly improved by adding 2-3 wt.%Mo and Fe simultaneously.
基金supported financially by the National Key Research and Development Program of China (No. 2016YFC1102402)the National Natural Science Foundation of China (No. 31570961)the Natural Science Foundation of Jiangsu Province (No. BK20160968)
文摘Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism, microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization （DRX） contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 ℃, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature （below 350 ℃）, the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 ℃ and 1 s^-1.
基金supported by the National Natural Science Foundation of China(No.51804232)Beijing Municipal Natural Science Foundation(No.2212041)+1 种基金supported by the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(FRF-IDRY-20-020)GIMRT Program of the Institute for Materials Research,Tohoku University(202303-RDKGE-0518).
文摘Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.
基金financial support from the National Natural Science Foundation of China(Nos.52233018 and 51831002)the China Baowu Low Carbon Metallurgy Innovation Foudation(No.BWLCF202213)。
文摘The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.
基金Item Sponsored by National Natrural Science Foundation of China(50734002)
文摘The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy exhibited a better crack resistance at higher temperature and lower strain rate.Microvoids initiated and coalesced into crack at subsurface on the equatorial plane of bulge surface under secondary tensile condition.The cracks were orientated at an angle of approximately 45° with respect to the compression axis due to the secondary tensile stress.Microcracks easily initiated on the interface of ferrite and austenite and propagated within ferrite.The predicted results using specific plastic work approach were matched well with the free surface cracks.
基金Funded by the National Natural Science Foundation of China(No.51575372)
文摘Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true stress-strain curves of the steel were characterized by hardening and subsequent softening and varied with temperatures and strain rates. The hot deformation activation energy of the steel was calculated to be 657.4 k J/mol, which was higher than that of the corresponding wrought steel due to its as-cast coarse columnar grains and heterogeneous structure. Hot processing maps were developed at different plastic strains, which exhibited two domains with peak power dissipation efficiencies at 1150 ℃/0.001 s^（-1） and 1200 ℃/1 s^（-1）, respectively. The corresponding microstructures were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, and electron backscatter diffraction（EBSD）. It has been confirmed that dynamic recrystallization（DRX） controlled by dislocation slipping and climbing mechanism occurs in the temperature and strain rate range of 1050-1200 ℃ and 0.001-0.01 s^（-1）; And DRX controlled by twinning mechanism occurs in the temperature and strain rate range of 1100-1200 ℃, 0.1-1 s^（-1）. These two DRX domains can serve as the hot working windows of the as-cast steel at lower strain rates and at higher strain rates, respectively. The processing maps at different strains also exhibit that the instability region decreases with increasing strain. The corresponding microstructures and the less tensile ductility in the instability region imply that the flow instability is attributed to flow localization accelerated by a few layers of very fine recrystallized grains along the original grain boundaries.
基金Supported by the National 863 Program of China(No.2015AA042505)Hubei Department of Education Youth Program(No.Q20123001)+1 种基金Hubei Province Natural Science Foundation(No.2014 cfb177)Wuhan Huaxia Fine Blanking Technology Co.,LTD Program(No.YYYY2014-015)
文摘The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on the hot deformation behavior of medium carbon steel was determined.The hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator deformed at temperatures from 850 to 1 200 ℃ and strain rates from 0.001 to 1 s^-1.The processing maps of two test steels were built at a true strain of 0.7 based on dynamic materials model（DMM）.There are two peak efficiency domains and two flow instability regions in both test steels.However,the peak efficiency domains of Nb-bearing steel move to higher temperature due to the inhibition of dynamic recrystaUization（DRX）,and the instability domains of Nb-bearing steel are enlarged due to the precipitation of Nb-containing particles during hot deformation.The optimum process parameters of Nb-bearing and Nb-free steels for industrial production were determined according to the processing map and the microstructural observation.
基金support from the National Natural Science Foundation of China, No.50771011
文摘Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.
文摘The deformation flow behaviors of Ti-45Al-5.4V-3.6Nb-0.3Y alloy at different temperatures and strain rates were studied by isothermal compressing simulation test.The apparent activation energy of deformation was calculated to be 402.096 kJ/mol and constitutive equation was established to describe the flow behavior.Microstructure and flow softening observations exhibited that Ti-45Al-5.4V3.6Nb-0.3Y alloy had bad hot workability at low temperature （lower than 1 100 oC） and high strain rate （higher than 0.5 s–1） characterized by localization deformation and instability.With deformation temperature higher than 1 150 oC and strain rate lower than 0.01 s–1,the alloy owned good hot deformability,and plenty of dynamic recrystallized grains could be observed in the deformed microstructures.
文摘Titanium has been widely used as the implant materials of joint prostheses. This paper simulates the microstructures of the hot forged titanium knee joint component by physical modeling. Ti-6Al-4V ELI were deformed by GLEEBLE 2000 hot deforma- tion simulator in compression mode to determine the hot workability, in the range of 900 to 1100℃, with the strain rates between 0.05 to 5 s^(-1). Test results derived from specimens processed by on-cooling test and on-heating test were compared, thereby estimating the effect due to thermal history. The forging process of Ti-6Al-4V ELI tibial base plate of knee joint prostheses was design based on the workability data obtained.
文摘TiAl base alloys have potential usage in aerospace engine for their high specific strength. In order to improve their poor hot workability, a new approach of hot deformation processing was investigated. The starting microstructure of Ti 46 5Al 2 5V 1 0Cr (atom percent, %) alloy is fully lamellar (FL) microstructure. The near gamma (NG) microstructure can be obtained through Nickel microalloying and heat treatment at 1 150 ℃. The isothermal compression tests were conducted on both materials using MTS machine at temperatures of 950 ℃, 1 000 ℃, and 1 050 ℃, and the strain rates of 0 01, 0 1 and 1 s -1 . Compared with the γ TiAl alloy with FL microstructure, the Ni bearing alloy with NG microstructure has better hot workability, such as enlarged hot workable region, decreased flow stresses, more uniform and finer deformed microstructure.
