For precise plastic deformation,microstructure control is essential especially for β-solidifying γ-TiAl alloy with duplex structure.Based on stereology,the microstructure of isothermally compressed γ-TiAl alloy was...For precise plastic deformation,microstructure control is essential especially for β-solidifying γ-TiAl alloy with duplex structure.Based on stereology,the microstructure of isothermally compressed γ-TiAl alloy was divided into β_(0) grains,remnant α_(2)/γ lamellar colonies,α_(2) and γ grains.The results show that the volume fraction of β_(0) grains slightly increases in the isothermally compressed γ-TiAl alloy with the increase of height reduction.Meanwhile,the volume fractions of remnant α_(2)/γ lamellar colonies and α_(2) grains decrease.However,the volume fraction of γ grains increases from 64.39% to 78.47%.According to the quantitative results,the α→γ phase transformation was investigated in-depth,and it is found that isothermal compression accelerates the α→γ phase transformation.The first α→γ phase transformation is similar to ledge-controlled transformation,through which remnant α_(2)/γ lamellar colonies finally convert intoγgrains in isothermal compression.The second is achieved by α/γ phase interface immigration.展开更多
The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallog...The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallographic results show that the globularization of α phase is sensitive to the parameters of deformation and heat treatment. By EBSD analysis, the formation and evolution mechanisms of intra-α boundaries are related to discontinuous dynamic recrystallization and continuous dynamic recrystallization, which can form α grains with high and low misorientations between neighbour grains after the heat treatment, respectively. Based on the globularization behavior and mechanism, two modified JMAK models are developed to predict the dynamic and static globularization kinetics, and the mean absolute relative errors(MARE) of 10.67% and 13.80% indicate the accuracy of the dynamic and static globularization kinetics models. The results of this work can provide guidance for controlling microstructure of titanium alloy.展开更多
The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% an...The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s^-1, and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries（HABs） remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr.展开更多
The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental r...The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 （θ phase） precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformatinn temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.展开更多
The physically-based internal state variable （ISV） models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. T...The physically-based internal state variable （ISV） models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1. The physically-based internal state variable models were implemented into the commercial finite element （FE） code. Then, a three-dimensional （3D） FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.展开更多
The microstructure evolution and its effect on flow stress of TC17 alloy during deformation in the α+β two-phase region were investigated via microstructure characterization and isothermal compression tests. Results...The microstructure evolution and its effect on flow stress of TC17 alloy during deformation in the α+β two-phase region were investigated via microstructure characterization and isothermal compression tests. Results showed that the spheroidized rate of α phase at 820 and 850℃ slightly increased with increasing strain. With increasing deformation temperature, the spheroidized rate of α phase showed a slight increasing trend, but the volume fraction of α phase significantly decreased. The flow stress at 780 ℃ and 1 s^-1 decreased continuously and steady state condition was not achieved up to strain of 1.2 due to dislocation annihilation and α lamellae rotation. Under this condition, the dynamic spheroidization was retarded. At the deformation temperatures of 820 and 850℃, and a strain rate of 1 s^-1, a steady state flow stress was observed at strains above 0.8 due to the balance between work hardening and dynamic softening. The dynamic softening was attributed to the α lamellae rotation, dynamic recovery and a little spheroidization.展开更多
The bulk TC17was subjected to the high energy shot peening(HESP)at the air pressures ranging from0.35to0.55MPa and processing durations ranging from15to60min.The microhardness(HV0.02)from topmost surface to matrix of ...The bulk TC17was subjected to the high energy shot peening(HESP)at the air pressures ranging from0.35to0.55MPa and processing durations ranging from15to60min.The microhardness(HV0.02)from topmost surface to matrix of the HESP processed TC17was measured,which generally decreases with the increase of depth from topmost surface to matrix and presents different variation with air pressure and processing duration at different depths.A fuzzy neural network(FNN)model was established to predict the surface layer microhardness of the HESP processed TC17,where the maximum and average difference between the measured and the predicted microhardness were respectively8.5%and3.2%.Applying the FNN model,the effects of the air pressure and processing duration on the microhardness at different depths were analyzed,revealing the significant interaction between the refined layer shelling and the continuous grain refinement.展开更多
The sensitivity analysis functions on globularized fraction ofαlamellae were established using a physically-based microstructure model and gradient method.These functions were applied to the sensitivity analysis on g...The sensitivity analysis functions on globularized fraction ofαlamellae were established using a physically-based microstructure model and gradient method.These functions were applied to the sensitivity analysis on globularized fraction ofαlamellae in TC17 alloy.The material constants in these functions are determined using the genetic algorithm-based objective optimization technique.The globularized fraction ofαlamellae during isothermal compression of TC17 alloy was quantitatively analyzed based on scanning electron microscopy(SEM)observation.The results show thatαlamellae mostly change to equiaxedαgrains at a deformation temperature of 1083 K,a strain rate of 0.01 s^-1 and a strain of 1.2.The globularized fraction decreases with increasing strain rate because lower strain rate provides enough time for the spheroidization.The effect of deformation temperature on the globularized fraction is controlled by the strain rate.And,the predicted derivations of globularized fraction with respect to processing parameters show good agreement with the experimental values.展开更多
In this study,isothermal compression tests were conducted at a Gleeble-1500 simulator at deformation temperatures ranging from 1073 to 1283 K,strain rates ranging from 0.01 to 5.00 s^（-1）,and height reductions rangi...In this study,isothermal compression tests were conducted at a Gleeble-1500 simulator at deformation temperatures ranging from 1073 to 1283 K,strain rates ranging from 0.01 to 5.00 s^（-1）,and height reductions ranging from 20%to 60%.The flow stress and apparent activation energy for deformation and constitutive equation were used to characterize the deformation behavior of TC21 alloy during the isothermal compression.The processing maps combined microstructure observations were established based on dynamic material model（DMM） over a range of strain rates and temperatures.The results show that an initial yield drop is observed above 1203 K or at higher strain rates ranging from 1.00 to 5.00 s^-1,and oscillatory flow curves are presented particularly at a strain rate of 5.00 s^-1.Strain has some influence on the apparent activation energy for deformation during the isothermal compression of TC21 alloy.The Q-values and microstructure observation confirm that dynamic recrystallization（DRX） occurs in the β single-phase region.The constitutive equation during the isothermal compression of TC21 alloy is developed using the Zener-Hollomon parameter in the exponent-type equation.The maximum and minimum relative errors between the calculated and the experimental flow stress are 14.1%and 0.3%,respectively.The peak efficiency of power dissipation at a strain of 0.7 is about 0.51 occurring at a deformation temperature of 1073 K and strain rate of 0.01 s^-1,corresponding to an optimal deformation condition of TC21 alloy.展开更多
The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play ...The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play a significant role in the flow behavior and microstructure evolution during isothermal compression of M50 steel. The average apparent activation energy for deformation in isothermal compression of M50 steel is （281.1±42.6） kJ·mol^-1 at the strains of 0.4-0.8. The dynamic recrystallization of austenite grains occurs in isothermal compression of M50 steel at 1 363 K and 1 393 K, enhancing with the increase of strain rate and/or strain. The volume fraction of the carbides decreases with the increase of deformation temperature during isothermal compression of M50 steel and the fine carbides inhibit the dynamic recrystallization of austenite grain. With the occurrence of dynamic recrystallization, the austenite grains are refined, leading to a minor increase in the flow stress and apparent activation energy for deformation in isothermal compression of M50 steel. The austenite grains begin to coarsen at 1 423 K and dynamic recrystallization is limited. Hot working of M50 steel should not be performed above 1 393 K in order to achieve good workability.展开更多
Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of ...Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of 0.8. The experimental results show that the flow stress increases with the decrease in the deformation temperature and the increase in the strain rate. The apparent activation energy for deformation is much lower at lower strain rates than that at higher strain rates. The flow stress model considering strain compensation was established. The average relative error between the calculated flow stress and experimental results is about 7.69%, indicating that the present model could be used to accurately predict the flow stress during high temperature in α＋β phase field of TC4 alloy.展开更多
The microstructure models were integrated into finite element（FE）code,and a three-dimensional（3D）FE analysis on the entire hot forging processes of 300 M steel large components was performed to predict the distrib...The microstructure models were integrated into finite element（FE）code,and a three-dimensional（3D）FE analysis on the entire hot forging processes of 300 M steel large components was performed to predict the distributions of effective strain,temperature field and austenite grain size.The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic recrystallization.However,coarse macro-grains appear in the minimum effective strain region.Then,300 M steel forging test was performed to validate the results of FE simulation,and microstructure observations and quantitative analysis were implemented.The average relative difference between the calculated and experimental austenite grain size is 7.56%,implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300 M steel.展开更多
Adiabatic shear band （ASB） was narrow region where softening occurred and concentrated plastic defor- mation took place. In present study, the effects of height reduction and deformation temperature on ASB were inve...Adiabatic shear band （ASB） was narrow region where softening occurred and concentrated plastic defor- mation took place. In present study, the effects of height reduction and deformation temperature on ASB were investigated by means of optical microscopy （OM） and scanning electron microscopy （SEM）. And the deformation mechanisms within the shear band were discussed thor- oughly with the help of transmission electron microscopy （TEM）. There is a critical strain for the formation of ASB during warm compression of Ti-6AI-4V alloy. The width of ASB increases with height reduction increasing. Elon- gated alpha grains within shear band grow up with defor- mation temperature increasing. Some ultrafine grains that confirm the occurrence of dynamic recrystallization are observed within shear band during warm compression of Ti-6AI-4V alloy.展开更多
Isothermal compression tests of Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb alloy were conducted at a Gleeble-1500 simulator in deformation temperature range of 1103–1243K, strain rate range of 0.01–5.00 s-1and height reduction ra...Isothermal compression tests of Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb alloy were conducted at a Gleeble-1500 simulator in deformation temperature range of 1103–1243K, strain rate range of 0.01–5.00 s-1and height reduction range of 50 %–70 %. The effects of processing parameters on morphology, grain size and contents of a and b phases were discussed based on the quantitative microstructure examination, and the detailed explanation was shown. The results show that b transformed matrix will obviously grow up at higher deformation temperature or lower strain rate because of low grain growth activation energies. The content of a phase will decrease at higher deformation temperature or higher strain rate due to the phase transformation. Some elongated a or b grains exist at higher strain rate, implying that the dominant softening mechanism is dynamic recovery. The effect of height reduction on b transformed matrix is negligible, but the height reduction has some effects on the morphology of primary a phase.展开更多
The variation of bonding ratio in the press bonding of TC4 alloy at temperatures from 850 to 900℃,pressures from 10 to 30 MPa,and time from 5 to 15 min was investigated.The bonding ratio increases with the increase o...The variation of bonding ratio in the press bonding of TC4 alloy at temperatures from 850 to 900℃,pressures from 10 to 30 MPa,and time from 5 to 15 min was investigated.The bonding ratio increases with the increase of temperature,time and pressure.The maximum bonding ratio,i.e.98 %,can be obtained at 900℃,30 MPa and 15 min.The significance and interaction of bonding parameters with the bonding ratio were investigated.The results demonstrate that the effect of pressure on the bonding ratio is the most effective and the effect of temperature is secondary,while the effect of time is not very powerful.The interaction of bonding parameter on the bonding ratio exists but that is distinguishing in different bonding parameter ranges.It is concluded that increasing pressure can be considered as the primary method to increase the bonding ratio.展开更多
基金the financial supports from the National Natural Science Foundation of China(No.51975478)the Fundamental Research Funds for the Central Universities,China(No.3102019MS0403).
文摘For precise plastic deformation,microstructure control is essential especially for β-solidifying γ-TiAl alloy with duplex structure.Based on stereology,the microstructure of isothermally compressed γ-TiAl alloy was divided into β_(0) grains,remnant α_(2)/γ lamellar colonies,α_(2) and γ grains.The results show that the volume fraction of β_(0) grains slightly increases in the isothermally compressed γ-TiAl alloy with the increase of height reduction.Meanwhile,the volume fractions of remnant α_(2)/γ lamellar colonies and α_(2) grains decrease.However,the volume fraction of γ grains increases from 64.39% to 78.47%.According to the quantitative results,the α→γ phase transformation was investigated in-depth,and it is found that isothermal compression accelerates the α→γ phase transformation.The first α→γ phase transformation is similar to ledge-controlled transformation,through which remnant α_(2)/γ lamellar colonies finally convert intoγgrains in isothermal compression.The second is achieved by α/γ phase interface immigration.
基金the support from the Science Fund for Distinguished Young Scholars from Shaanxi Province, China (No. 2020JC-17)the National Natural Science Foundation of China (No. 51705425)+1 种基金the Research Fund of the State Key Laboratory of Solidification Processing (NWPU), China (No. 2019-QZ-04)the Fundamental Research Funds for the Central Universities, China (No. 3102019PY007)。
文摘The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallographic results show that the globularization of α phase is sensitive to the parameters of deformation and heat treatment. By EBSD analysis, the formation and evolution mechanisms of intra-α boundaries are related to discontinuous dynamic recrystallization and continuous dynamic recrystallization, which can form α grains with high and low misorientations between neighbour grains after the heat treatment, respectively. Based on the globularization behavior and mechanism, two modified JMAK models are developed to predict the dynamic and static globularization kinetics, and the mean absolute relative errors(MARE) of 10.67% and 13.80% indicate the accuracy of the dynamic and static globularization kinetics models. The results of this work can provide guidance for controlling microstructure of titanium alloy.
基金Project(51275416)supported by the National Natural Science Foundation of ChinaProject(KP201513)supported by the Fund of the State Key Laboratory of Solidification Processing in NWPU,China
文摘The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^-1, deformation amount（height reduction） 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s^-1, and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries（HABs） remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr.
基金supported by the Foundational Research Plan of Jiangsu Province,China (NoBK2005025)
文摘The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 （θ phase） precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformatinn temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.
基金supported by the National Natural Science Foundation of China (No.50975234)China Postdoctoral Science Foundation (No.20110491685)
文摘The physically-based internal state variable （ISV） models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1. The physically-based internal state variable models were implemented into the commercial finite element （FE） code. Then, a three-dimensional （3D） FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.
基金Project(51575446)supported by the National Natural Science Foundation of ChinaProject(2017KJXX-27)supported by the Shaanxi Province Youth Science and Technology New Star Plan,ChinaProject(3102017AX003)supported by the Fundamental Research Funds for the Central Universities,China
文摘The microstructure evolution and its effect on flow stress of TC17 alloy during deformation in the α+β two-phase region were investigated via microstructure characterization and isothermal compression tests. Results showed that the spheroidized rate of α phase at 820 and 850℃ slightly increased with increasing strain. With increasing deformation temperature, the spheroidized rate of α phase showed a slight increasing trend, but the volume fraction of α phase significantly decreased. The flow stress at 780 ℃ and 1 s^-1 decreased continuously and steady state condition was not achieved up to strain of 1.2 due to dislocation annihilation and α lamellae rotation. Under this condition, the dynamic spheroidization was retarded. At the deformation temperatures of 820 and 850℃, and a strain rate of 1 s^-1, a steady state flow stress was observed at strains above 0.8 due to the balance between work hardening and dynamic softening. The dynamic softening was attributed to the α lamellae rotation, dynamic recovery and a little spheroidization.
基金Project (51475375) supported by the National Natural Science Foundation of China
文摘The bulk TC17was subjected to the high energy shot peening(HESP)at the air pressures ranging from0.35to0.55MPa and processing durations ranging from15to60min.The microhardness(HV0.02)from topmost surface to matrix of the HESP processed TC17was measured,which generally decreases with the increase of depth from topmost surface to matrix and presents different variation with air pressure and processing duration at different depths.A fuzzy neural network(FNN)model was established to predict the surface layer microhardness of the HESP processed TC17,where the maximum and average difference between the measured and the predicted microhardness were respectively8.5%and3.2%.Applying the FNN model,the effects of the air pressure and processing duration on the microhardness at different depths were analyzed,revealing the significant interaction between the refined layer shelling and the continuous grain refinement.
基金Project(51575446) supported by the National Natural Science Foundation of ChinaProject(2016JQ5070) supported by the Natural Science Basis Research Plan of Shaanxi Province,China+1 种基金Project(2017KJXX-27) supported by the Youth Science and Technology New Star Plan of Shaanxi Province,ChinaProject(3102017AX003) supported by the Fundamental Research Funds for the Central Universities,China
文摘The sensitivity analysis functions on globularized fraction ofαlamellae were established using a physically-based microstructure model and gradient method.These functions were applied to the sensitivity analysis on globularized fraction ofαlamellae in TC17 alloy.The material constants in these functions are determined using the genetic algorithm-based objective optimization technique.The globularized fraction ofαlamellae during isothermal compression of TC17 alloy was quantitatively analyzed based on scanning electron microscopy(SEM)observation.The results show thatαlamellae mostly change to equiaxedαgrains at a deformation temperature of 1083 K,a strain rate of 0.01 s^-1 and a strain of 1.2.The globularized fraction decreases with increasing strain rate because lower strain rate provides enough time for the spheroidization.The effect of deformation temperature on the globularized fraction is controlled by the strain rate.And,the predicted derivations of globularized fraction with respect to processing parameters show good agreement with the experimental values.
基金financially supported by the National Natural Science Foundation of China(No.51205318)the University Student’s Innovation Training Program(No.201310699016)
文摘In this study,isothermal compression tests were conducted at a Gleeble-1500 simulator at deformation temperatures ranging from 1073 to 1283 K,strain rates ranging from 0.01 to 5.00 s^（-1）,and height reductions ranging from 20%to 60%.The flow stress and apparent activation energy for deformation and constitutive equation were used to characterize the deformation behavior of TC21 alloy during the isothermal compression.The processing maps combined microstructure observations were established based on dynamic material model（DMM） over a range of strain rates and temperatures.The results show that an initial yield drop is observed above 1203 K or at higher strain rates ranging from 1.00 to 5.00 s^-1,and oscillatory flow curves are presented particularly at a strain rate of 5.00 s^-1.Strain has some influence on the apparent activation energy for deformation during the isothermal compression of TC21 alloy.The Q-values and microstructure observation confirm that dynamic recrystallization（DRX） occurs in the β single-phase region.The constitutive equation during the isothermal compression of TC21 alloy is developed using the Zener-Hollomon parameter in the exponent-type equation.The maximum and minimum relative errors between the calculated and the experimental flow stress are 14.1%and 0.3%,respectively.The peak efficiency of power dissipation at a strain of 0.7 is about 0.51 occurring at a deformation temperature of 1073 K and strain rate of 0.01 s^-1,corresponding to an optimal deformation condition of TC21 alloy.
文摘The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play a significant role in the flow behavior and microstructure evolution during isothermal compression of M50 steel. The average apparent activation energy for deformation in isothermal compression of M50 steel is （281.1±42.6） kJ·mol^-1 at the strains of 0.4-0.8. The dynamic recrystallization of austenite grains occurs in isothermal compression of M50 steel at 1 363 K and 1 393 K, enhancing with the increase of strain rate and/or strain. The volume fraction of the carbides decreases with the increase of deformation temperature during isothermal compression of M50 steel and the fine carbides inhibit the dynamic recrystallization of austenite grain. With the occurrence of dynamic recrystallization, the austenite grains are refined, leading to a minor increase in the flow stress and apparent activation energy for deformation in isothermal compression of M50 steel. The austenite grains begin to coarsen at 1 423 K and dynamic recrystallization is limited. Hot working of M50 steel should not be performed above 1 393 K in order to achieve good workability.
基金financially supported by China Postdoctoral Science Foundation (No. 2017M610649)Fundamental Research Funds for the Central Universities (No. 3102017zy001)
文摘Isothermal compression of TC4 alloy was performed on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1093 to 1243 K, the strain rates ranging from 0.001 to 10.000 s^-l and a maximum strain of 0.8. The experimental results show that the flow stress increases with the decrease in the deformation temperature and the increase in the strain rate. The apparent activation energy for deformation is much lower at lower strain rates than that at higher strain rates. The flow stress model considering strain compensation was established. The average relative error between the calculated flow stress and experimental results is about 7.69%, indicating that the present model could be used to accurately predict the flow stress during high temperature in α＋β phase field of TC4 alloy.
基金Item Sponsored by National Natural Science Foundation of China(51575446)Natural Science Basis Research Plan in Shaanxi Province of China(2016JQ5070)
文摘The microstructure models were integrated into finite element（FE）code,and a three-dimensional（3D）FE analysis on the entire hot forging processes of 300 M steel large components was performed to predict the distributions of effective strain,temperature field and austenite grain size.The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic recrystallization.However,coarse macro-grains appear in the minimum effective strain region.Then,300 M steel forging test was performed to validate the results of FE simulation,and microstructure observations and quantitative analysis were implemented.The average relative difference between the calculated and experimental austenite grain size is 7.56%,implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300 M steel.
基金financially supported by the National Natural Science Foundation of China(No.51575446)the Fundamental Research Funds for the Central Universities(No.3102014JCQ01016)
文摘Adiabatic shear band （ASB） was narrow region where softening occurred and concentrated plastic defor- mation took place. In present study, the effects of height reduction and deformation temperature on ASB were investigated by means of optical microscopy （OM） and scanning electron microscopy （SEM）. And the deformation mechanisms within the shear band were discussed thor- oughly with the help of transmission electron microscopy （TEM）. There is a critical strain for the formation of ASB during warm compression of Ti-6AI-4V alloy. The width of ASB increases with height reduction increasing. Elon- gated alpha grains within shear band grow up with defor- mation temperature increasing. Some ultrafine grains that confirm the occurrence of dynamic recrystallization are observed within shear band during warm compression of Ti-6AI-4V alloy.
基金financially supported by the National Natural Science Foundation of China (No. 51205318)the Fundamental Research Funds for the Central Universities (No. 3102014JCQ01016)the University Student’s Innovation Training Program (No. 201410699020)
文摘Isothermal compression tests of Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb alloy were conducted at a Gleeble-1500 simulator in deformation temperature range of 1103–1243K, strain rate range of 0.01–5.00 s-1and height reduction range of 50 %–70 %. The effects of processing parameters on morphology, grain size and contents of a and b phases were discussed based on the quantitative microstructure examination, and the detailed explanation was shown. The results show that b transformed matrix will obviously grow up at higher deformation temperature or lower strain rate because of low grain growth activation energies. The content of a phase will decrease at higher deformation temperature or higher strain rate due to the phase transformation. Some elongated a or b grains exist at higher strain rate, implying that the dominant softening mechanism is dynamic recovery. The effect of height reduction on b transformed matrix is negligible, but the height reduction has some effects on the morphology of primary a phase.
基金financially supported by the National Natural Science Foundation of China (No.51275416)
文摘The variation of bonding ratio in the press bonding of TC4 alloy at temperatures from 850 to 900℃,pressures from 10 to 30 MPa,and time from 5 to 15 min was investigated.The bonding ratio increases with the increase of temperature,time and pressure.The maximum bonding ratio,i.e.98 %,can be obtained at 900℃,30 MPa and 15 min.The significance and interaction of bonding parameters with the bonding ratio were investigated.The results demonstrate that the effect of pressure on the bonding ratio is the most effective and the effect of temperature is secondary,while the effect of time is not very powerful.The interaction of bonding parameter on the bonding ratio exists but that is distinguishing in different bonding parameter ranges.It is concluded that increasing pressure can be considered as the primary method to increase the bonding ratio.
