High temperature deformation characteristics of a semiaustenitic grade of precipitation-hardening stain- less steels were investigated by conducting hot compression tests at temperatures of 900--1 100 ℃ and strain ra...High temperature deformation characteristics of a semiaustenitic grade of precipitation-hardening stain- less steels were investigated by conducting hot compression tests at temperatures of 900--1 100 ℃ and strain rates of 0. 001--1 s^-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and de- formation parameters including temperature and strain rate, and therefore, Zener-Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as-deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed.展开更多
Multipass plain strain compression test of 7055 alloy was carried out on Gleeble 1500D thermomechanical simulator to study the effect of interval time on static softening behavior between two passes. Microstructural f...Multipass plain strain compression test of 7055 alloy was carried out on Gleeble 1500D thermomechanical simulator to study the effect of interval time on static softening behavior between two passes. Microstructural features of the alloy deformed with delay times varying from 0 to 180 s after achieving a reduction of ,-~52 % in the 13 stages was investigated through TEM and EBSD observations. The 14th pass of peak stresses after different delay times were gained. The peak stress decreases with the interstage delay time increasing, but the decreasing trend is gradually slower. Static recovery, metadynamic recrystallization, and/or static recrystallization can be found in the alloy during two passes. The recovery and recrystallization degree increases with longer interstage delay time. The static recovery is the main softening mechanism. Subgrain coalescence and subgrain growth together with particle-stimulated nucleation are the main nucleation mechanisms for static recrystallization.展开更多
The effects of process parameters on the microstructural evolution, includinggrain size and volume traction of the a phase during hot forming of a TC6 alloy were investigatedusing compression tests. Experiments were c...The effects of process parameters on the microstructural evolution, includinggrain size and volume traction of the a phase during hot forming of a TC6 alloy were investigatedusing compression tests. Experiments were conducted on the material with (α + β) phases atdeformation temperatures of 800, 860, 920, and 950℃, strain rates of 0.001, 0.01, 1, and 50 s^(-1),and height direction reductions of 30%, 40%, and 50%. After reaching a peak value near 920℃, thegrain size and volume fraction decrease with further increase of deformation temperature. The strainrate affects the morphologies and grain size of α phase of the TC6 titanium alloy. At a lowerstrain rate, the effect of the strain rate on the volume fraction is greater than that at a higherstrain rate under the experimental conditions. The effects of the strain rate on the microstructurealso result from deformation heating. The grain size of the α phase increases with an increase inheight direction reduction after an early drop. The effect of height direction reduction on thevolume fraction is similar to that of the grain size. All of the optical micrographs andquantitative metallography show that deformation process parameters affect the microstructure duringhot forming of the TC6 alloy, and a correlation between the temperature, strain, and strain rateappears to be a significant fuzzy characteristic.展开更多
The hot deformation behaviors of TA15 alloy,as well as the microstructure obtained after compressive deformation,were investigated.The results show that TA15 alloy exhibits a peak stress when deformed at temperature l...The hot deformation behaviors of TA15 alloy,as well as the microstructure obtained after compressive deformation,were investigated.The results show that TA15 alloy exhibits a peak stress when deformed at temperature lower than 900 ℃,implying recrystallization characteristics.However,steady flow stress-stain behavior is observed without peak stress when deformation is employed at temperature higher than 900 ℃,showing recovery characteristics.Micro-deformation band appears at deformation temperature of 750 ℃,and equiaxed grains are found at 800 ℃,implying the occurrence of recrystallization.When deformed at 925 ℃,the specimen shows the recovery characteristics with dislocation networks and sub-grain boundaries.展开更多
The relationship of true stress and true strain of AZ41M magnesium alloy under twin-roll-cast (TRC) and hot compression was analyzed us- ing a Gleeble 1500 machine. Microstructural evolutions of the TRC magnesium al...The relationship of true stress and true strain of AZ41M magnesium alloy under twin-roll-cast (TRC) and hot compression was analyzed us- ing a Gleeble 1500 machine. Microstructural evolutions of the TRC magnesium alloy under different deformation conditions (strain, sWain rate and deformation temperature) were examined using optical microscopy and discussed. The relationship of true stress and true sWain pre- dicted that lower deformation temperature and higher sWain rate caused sharp strain hardening. Meanwhile, the flow stress curve turned into a steady state at high temperature and lower strain rate. The intermediate temperature and strain rate (623 K and 0.01 s^-1) is appropriate.展开更多
The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation tem...The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.展开更多
The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flo...The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flow due to isostatic pressure and movement of solid particles due to shear force. Deformation condition depends on the nucleation rate and closure rate of the cavities. The flow stress slightly varies when the difference between the nucleation rate and closure rate of the cavities is small; however, it decreases when the nucleation rate of the cavities is greater than the closure rate of the cavities.展开更多
A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation (DEFT) through a series of hot compression tests. In addition, the influence of prior au...A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation (DEFT) through a series of hot compression tests. In addition, the influence of prior austenite grain size (PAGS) on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.展开更多
The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator...The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al;Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.展开更多
A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results sho...A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results show that deformation temperature influences the work-hardening behavior of the matrix and the rotation behavior of the whiskers. With increasing temperature, the work hardening rate of the matrix decreases, but the whisker rotation angle increases. Both whisker rotation and the increase of deformation temperature can induce reductions in the load supported by whisker and the load transferred from matrix to whisker. Additionally, it is found that during large strain deformation at higher temperatures, the enhancing of deformation temperature can reduce the effect of whisker rotation. Meanwhile, the stress-strain behavior of the composite is rather sensitive to deformation temperature. At a relatively lower temperature (150℃), the composite exhibits work hardening due to the matrix work hardening, but at relatively higher temperatures (300℃ and above), the composite shows strain softening due to whisker rotation. It is also found that during hot compression at higher temperatures, the softening rate of the composite decreases with increasing temperature. The predicted stress-strain behavior of the composite is approximately in agreement with the experimental results.展开更多
TC11 titanium alloy samples with lamellar microstructrue were compressed on a Gleeble 1500D Simulator.Compression tests were carried out at 950 ℃ and a strain rate of 0.1 s-1 with height reduction of 20%,40% and 60%,...TC11 titanium alloy samples with lamellar microstructrue were compressed on a Gleeble 1500D Simulator.Compression tests were carried out at 950 ℃ and a strain rate of 0.1 s-1 with height reduction of 20%,40% and 60%,respectively.Microstruture of the compressed TC11 alloy was obeserved and analyzed by optical microscopy(OM),transmission electron microscope(TEM),electron back-scattered diffraction(EBSD).The lamellar disintegration mechanism of the TC11 titanium alloy was deduced.The results indicated that the compressive deformation promoted the phase transformation in bi-phase area.βphase layers were formed along the gliding planes inα phase,and α slivers were disintegrated into many small flakes through theα/βinterface slipping.展开更多
Hot compressive behaviors of Ti-6Al-2Zr-1Mo-1V alloy at 800℃, as well as the evolution of microstructure during deformation process, were investigated. The experimental results show that flow stress increases to a pe...Hot compressive behaviors of Ti-6Al-2Zr-1Mo-1V alloy at 800℃, as well as the evolution of microstructure during deformation process, were investigated. The experimental results show that flow stress increases to a peak stress followed by a decease with increasing strain, and finally forms a stable stage. Dislocations are generated at the interface of αβ phase, and the phase interface and dislocation loops play an important role in impeding the movement of dislocation. As strain increasing, micro-deformation bands with high-density dislocation are formed, and dynamic recrystallizaton occurs finally. XRD Fourier analysis reveals that dislocation density increases followed by a decrease during compressive deformation, and falls into the range from 10^10 to 10^11 cm^-2.展开更多
The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscat...The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscatter diffraction (EBSD) and X-ray diffraction (XRD).The deformation condition of hot compression is 350 ℃,0.1 s?1.The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed.The results show that TRC provides more modified microstructure compared with DC.Twins are found in TRC processing;dynamic recrystallization (DRX),shear bands and twins are found in TRC-HC.A short annealing time has little effect on hardness,while during a long time annealing,it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.展开更多
The samples of TA15 titanium alloy were hot compressed in the temperature range of 550-1 000℃at constant strain rate from 0.01 s-1 to 1.0 s-1.The flow behavior and microstructural evolution during hot deformation of ...The samples of TA15 titanium alloy were hot compressed in the temperature range of 550-1 000℃at constant strain rate from 0.01 s-1 to 1.0 s-1.The flow behavior and microstructural evolution during hot deformation of TA15 alloy were investigated, based on which the hot working parameters of TA15 alloy were selected. The results show that with the increase of deformation temperature and decrease of stain rate, the flow stress decreases gradually, but the magnitude of stress drop varies with the increase of temperature in different temperature intervals. According to the flow stress and deformation microstructure, the deformation behavior can be classified into three types as working hardening(550-600℃,α+βphase), dynamic recrystallization (650-900℃,α+βphase) and dynamic recovery(950-1 000℃,βphase). The main softening mechanism is dynamic recrystallization(DRX) ofαphase inα+βphase zone and dynamic recovery(DRV) ofβphase inβphase zone. As the stain rate decreases dynamic recrystallization ofαphase proceeds more adequately inα+βzone and theβsubgrains of dynamic recovery have the tendency to grow inβzone. The reasonable temperature for warm forming of TA15 alloy is in the range of 600-700℃, which has been verified by warm spinning experiment of tube workpieces.展开更多
The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were prefor...The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.展开更多
A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructu...A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress,strain,strain rates and deformation temperatures.Statistical analysis shows the validity of the proposed model.The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile,the flow stress curve turns into a steady state at high temperature and lower strain rate.The moderate temperature of 350 ℃and strain rate of 0.01 s-1 are appropriate to this alloy.展开更多
The flow stress features of MB26 magnesium alloy were studied by isothermal compression at 300-450 ℃ and strain rate of 0.001-1 s-1 with Gleeble 1500 thermal simulator. In addition,the deformation activation energy Q...The flow stress features of MB26 magnesium alloy were studied by isothermal compression at 300-450 ℃ and strain rate of 0.001-1 s-1 with Gleeble 1500 thermal simulator. In addition,the deformation activation energy Q was calculated. The results show that the strain rate and deformation temperature have obvious effect on the true stress. The peak value of flow stress becomes larger with increasing strain rate at the same temperature,and gets smaller with the increasing deformation temperature at the same strain rate. The alloy shows partial dynamic recrystallization. The flow stress of MB26 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter including the Arrhemius term. The temperature range of 350-400 ℃ is suggested for hot-forming of this alloy.展开更多
The flow stress behavior of 2197 Al-Li alloy during hot compression deformation was studied in the strain rate range from 0.01 to 10 s-1 and the temperature range from 360 to 510 ℃ by isothermal compression test on a...The flow stress behavior of 2197 Al-Li alloy during hot compression deformation was studied in the strain rate range from 0.01 to 10 s-1 and the temperature range from 360 to 510 ℃ by isothermal compression test on a Gleeble-1500 thermal-mechanical simulator. The results show that the flow stress of 2197 Al-Li alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The peak flow stress during high temperature deformation can be represented by Z parameter in a hyperbolic sine function. The analytical expression of peak flow stress was fitted with the hot deformation activation energy of 260.6 kJ/mol.展开更多
Finite element analysis was used to investigate the effects of whisker misalignment on the hot compressive deformation behavior of whisker-reinforced composites. The simulation provided the evolution of the stress fie...Finite element analysis was used to investigate the effects of whisker misalignment on the hot compressive deformation behavior of whisker-reinforced composites. The simulation provided the evolution of the stress field of the composites and the whisker rotation process. It is found that with increasing the angle of whisker misalignment the whisker rotation angle decreases. Meanwhile, the mechanical behaviors of the composites such as work hardening or strain softening are affected by the whisker orientation and rotation during the hot compressive deformation. The predicted results are in agreement with the experimental results.展开更多
文摘High temperature deformation characteristics of a semiaustenitic grade of precipitation-hardening stain- less steels were investigated by conducting hot compression tests at temperatures of 900--1 100 ℃ and strain rates of 0. 001--1 s^-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and de- formation parameters including temperature and strain rate, and therefore, Zener-Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as-deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed.
基金financially supported by the Natural Science Foundation of Inner Mongolia (No. 2011bs0802)Research Fund for the Higher Education of Inner Mongolia (No. NJZY11075)
文摘Multipass plain strain compression test of 7055 alloy was carried out on Gleeble 1500D thermomechanical simulator to study the effect of interval time on static softening behavior between two passes. Microstructural features of the alloy deformed with delay times varying from 0 to 180 s after achieving a reduction of ,-~52 % in the 13 stages was investigated through TEM and EBSD observations. The 14th pass of peak stresses after different delay times were gained. The peak stress decreases with the interstage delay time increasing, but the decreasing trend is gradually slower. Static recovery, metadynamic recrystallization, and/or static recrystallization can be found in the alloy during two passes. The recovery and recrystallization degree increases with longer interstage delay time. The static recovery is the main softening mechanism. Subgrain coalescence and subgrain growth together with particle-stimulated nucleation are the main nucleation mechanisms for static recrystallization.
基金This work was financially supported by the Ministry of Science and Technology (No. G2000067206)the Teaching and Research Award Fund for Outstanding Young Teachers in Higher Education Institutions of MOE, China
文摘The effects of process parameters on the microstructural evolution, includinggrain size and volume traction of the a phase during hot forming of a TC6 alloy were investigatedusing compression tests. Experiments were conducted on the material with (α + β) phases atdeformation temperatures of 800, 860, 920, and 950℃, strain rates of 0.001, 0.01, 1, and 50 s^(-1),and height direction reductions of 30%, 40%, and 50%. After reaching a peak value near 920℃, thegrain size and volume fraction decrease with further increase of deformation temperature. The strainrate affects the morphologies and grain size of α phase of the TC6 titanium alloy. At a lowerstrain rate, the effect of the strain rate on the volume fraction is greater than that at a higherstrain rate under the experimental conditions. The effects of the strain rate on the microstructurealso result from deformation heating. The grain size of the α phase increases with an increase inheight direction reduction after an early drop. The effect of height direction reduction on thevolume fraction is similar to that of the grain size. All of the optical micrographs andquantitative metallography show that deformation process parameters affect the microstructure duringhot forming of the TC6 alloy, and a correlation between the temperature, strain, and strain rateappears to be a significant fuzzy characteristic.
文摘The hot deformation behaviors of TA15 alloy,as well as the microstructure obtained after compressive deformation,were investigated.The results show that TA15 alloy exhibits a peak stress when deformed at temperature lower than 900 ℃,implying recrystallization characteristics.However,steady flow stress-stain behavior is observed without peak stress when deformation is employed at temperature higher than 900 ℃,showing recovery characteristics.Micro-deformation band appears at deformation temperature of 750 ℃,and equiaxed grains are found at 800 ℃,implying the occurrence of recrystallization.When deformed at 925 ℃,the specimen shows the recovery characteristics with dislocation networks and sub-grain boundaries.
基金supported by the Natural Science Foundation of Shandong Province (Nos Y2008F27 and ZR2009FL003)the S&T Developing Program of Shandong Province, China (2007GG10004013)the Doctoral Foundation of University of Jinan (XBS0830)
文摘The relationship of true stress and true strain of AZ41M magnesium alloy under twin-roll-cast (TRC) and hot compression was analyzed us- ing a Gleeble 1500 machine. Microstructural evolutions of the TRC magnesium alloy under different deformation conditions (strain, sWain rate and deformation temperature) were examined using optical microscopy and discussed. The relationship of true stress and true sWain pre- dicted that lower deformation temperature and higher sWain rate caused sharp strain hardening. Meanwhile, the flow stress curve turned into a steady state at high temperature and lower strain rate. The intermediate temperature and strain rate (623 K and 0.01 s^-1) is appropriate.
基金This work was financially supported by the National Basic Research Program of China (No. G20000672).
文摘The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.
基金This study was financially supported by the National Basic Research Program of China (No. G20000672).
文摘The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flow due to isostatic pressure and movement of solid particles due to shear force. Deformation condition depends on the nucleation rate and closure rate of the cavities. The flow stress slightly varies when the difference between the nucleation rate and closure rate of the cavities is small; however, it decreases when the nucleation rate of the cavities is greater than the closure rate of the cavities.
基金This work was financially supported by the National Science and Technology Ministry to the research project ‘Advanced industriali-zation technique of manufacture for carbon steel of 500 MPa grade’ (No.2001AA332020).
文摘A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation (DEFT) through a series of hot compression tests. In addition, the influence of prior austenite grain size (PAGS) on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.
基金Sichuan Provincial Development and Reform Commission for funding this work by Panxi Strategic Resources Innovation Development Fund (2015)the department of Science and Technology of Sichuan Province (2015GZ0052)
文摘The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al;Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.
基金This study was financially supported by the National Natural Science Foundation of China (No. 50071008).
文摘A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results show that deformation temperature influences the work-hardening behavior of the matrix and the rotation behavior of the whiskers. With increasing temperature, the work hardening rate of the matrix decreases, but the whisker rotation angle increases. Both whisker rotation and the increase of deformation temperature can induce reductions in the load supported by whisker and the load transferred from matrix to whisker. Additionally, it is found that during large strain deformation at higher temperatures, the enhancing of deformation temperature can reduce the effect of whisker rotation. Meanwhile, the stress-strain behavior of the composite is rather sensitive to deformation temperature. At a relatively lower temperature (150℃), the composite exhibits work hardening due to the matrix work hardening, but at relatively higher temperatures (300℃ and above), the composite shows strain softening due to whisker rotation. It is also found that during hot compression at higher temperatures, the softening rate of the composite decreases with increasing temperature. The predicted stress-strain behavior of the composite is approximately in agreement with the experimental results.
基金Funded by the National Key Natural Science Foundation of China(No.5131903ZT1)
文摘TC11 titanium alloy samples with lamellar microstructrue were compressed on a Gleeble 1500D Simulator.Compression tests were carried out at 950 ℃ and a strain rate of 0.1 s-1 with height reduction of 20%,40% and 60%,respectively.Microstruture of the compressed TC11 alloy was obeserved and analyzed by optical microscopy(OM),transmission electron microscope(TEM),electron back-scattered diffraction(EBSD).The lamellar disintegration mechanism of the TC11 titanium alloy was deduced.The results indicated that the compressive deformation promoted the phase transformation in bi-phase area.βphase layers were formed along the gliding planes inα phase,and α slivers were disintegrated into many small flakes through theα/βinterface slipping.
文摘Hot compressive behaviors of Ti-6Al-2Zr-1Mo-1V alloy at 800℃, as well as the evolution of microstructure during deformation process, were investigated. The experimental results show that flow stress increases to a peak stress followed by a decease with increasing strain, and finally forms a stable stage. Dislocations are generated at the interface of αβ phase, and the phase interface and dislocation loops play an important role in impeding the movement of dislocation. As strain increasing, micro-deformation bands with high-density dislocation are formed, and dynamic recrystallizaton occurs finally. XRD Fourier analysis reveals that dislocation density increases followed by a decrease during compressive deformation, and falls into the range from 10^10 to 10^11 cm^-2.
基金Project(10020072) supported by the Korean Ministry of Commerce,Industry and EnergyProject(Y2008F27) supported by the Natural Science Foundation of Shandong Province,China
文摘The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscatter diffraction (EBSD) and X-ray diffraction (XRD).The deformation condition of hot compression is 350 ℃,0.1 s?1.The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed.The results show that TRC provides more modified microstructure compared with DC.Twins are found in TRC processing;dynamic recrystallization (DRX),shear bands and twins are found in TRC-HC.A short annealing time has little effect on hardness,while during a long time annealing,it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.
文摘The samples of TA15 titanium alloy were hot compressed in the temperature range of 550-1 000℃at constant strain rate from 0.01 s-1 to 1.0 s-1.The flow behavior and microstructural evolution during hot deformation of TA15 alloy were investigated, based on which the hot working parameters of TA15 alloy were selected. The results show that with the increase of deformation temperature and decrease of stain rate, the flow stress decreases gradually, but the magnitude of stress drop varies with the increase of temperature in different temperature intervals. According to the flow stress and deformation microstructure, the deformation behavior can be classified into three types as working hardening(550-600℃,α+βphase), dynamic recrystallization (650-900℃,α+βphase) and dynamic recovery(950-1 000℃,βphase). The main softening mechanism is dynamic recrystallization(DRX) ofαphase inα+βphase zone and dynamic recovery(DRV) ofβphase inβphase zone. As the stain rate decreases dynamic recrystallization ofαphase proceeds more adequately inα+βzone and theβsubgrains of dynamic recovery have the tendency to grow inβzone. The reasonable temperature for warm forming of TA15 alloy is in the range of 600-700℃, which has been verified by warm spinning experiment of tube workpieces.
基金Project(2002AA305104) supported by the National High-Tech Research and Development Program of China
文摘The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.
基金Project(Y2008F27)supported by the Natural Science Foundation of Shandong Province,China
文摘A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress,strain,strain rates and deformation temperatures.Statistical analysis shows the validity of the proposed model.The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile,the flow stress curve turns into a steady state at high temperature and lower strain rate.The moderate temperature of 350 ℃and strain rate of 0.01 s-1 are appropriate to this alloy.
文摘The flow stress features of MB26 magnesium alloy were studied by isothermal compression at 300-450 ℃ and strain rate of 0.001-1 s-1 with Gleeble 1500 thermal simulator. In addition,the deformation activation energy Q was calculated. The results show that the strain rate and deformation temperature have obvious effect on the true stress. The peak value of flow stress becomes larger with increasing strain rate at the same temperature,and gets smaller with the increasing deformation temperature at the same strain rate. The alloy shows partial dynamic recrystallization. The flow stress of MB26 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter including the Arrhemius term. The temperature range of 350-400 ℃ is suggested for hot-forming of this alloy.
基金Project(MKPT-2004-19ZD) supported by the National Defense Science, Technology and Industry Committee of China
文摘The flow stress behavior of 2197 Al-Li alloy during hot compression deformation was studied in the strain rate range from 0.01 to 10 s-1 and the temperature range from 360 to 510 ℃ by isothermal compression test on a Gleeble-1500 thermal-mechanical simulator. The results show that the flow stress of 2197 Al-Li alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The peak flow stress during high temperature deformation can be represented by Z parameter in a hyperbolic sine function. The analytical expression of peak flow stress was fitted with the hot deformation activation energy of 260.6 kJ/mol.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50071008).
文摘Finite element analysis was used to investigate the effects of whisker misalignment on the hot compressive deformation behavior of whisker-reinforced composites. The simulation provided the evolution of the stress field of the composites and the whisker rotation process. It is found that with increasing the angle of whisker misalignment the whisker rotation angle decreases. Meanwhile, the mechanical behaviors of the composites such as work hardening or strain softening are affected by the whisker orientation and rotation during the hot compressive deformation. The predicted results are in agreement with the experimental results.