Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dyna...Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.展开更多
In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of...In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of1000?1200°C and strain raterange of0.001?10s?1on a Gleeble?3800thermo-mechanical simulator.The results reveal that the flow stress is sensitive to the strainrate,and the dynamic recrystallization(DRX)is the principal softening mechanism.The strain rate of0.1s?1is considered to be thecritical point during the hot deformation at1000°C.The DRX process is closely related to the strain rate due to the adiabatictemperature rise.The strain rate has an important influence on DDRX and CDRX during hot deformation.The nucleation of DRXcan be activated by twin boundaries,and there is a lower fraction ofΣ3n(n=1,2,3)boundaries at the intermediate strain rate of0.1s?1.展开更多
The characteristics of dynamic recrystallization （DRX） in Mg-Y-Nd-Gd-Zr-RE magnesium alloy were investigated by compression tests at temperatures between 523 and 723 K and at strain rates ranging from 0.002 to 1 s^-...The characteristics of dynamic recrystallization （DRX） in Mg-Y-Nd-Gd-Zr-RE magnesium alloy were investigated by compression tests at temperatures between 523 and 723 K and at strain rates ranging from 0.002 to 1 s^-1 with maximum strain of 0.693. The strainhardening rate can be obtained from true stress-true strain curves, plots of θ-σ, -（δθ/δσ-）-a and lnθ-σ in different compression conditions were obtained by further study. The critical condition of the onset of DRX process was determined as （（δ/δσ（ δθ/δσ））=0. In the range of the above deformation temperature and strain rate, the ratio of critical stress （σc） to peak stress （σm） and critical strain （εc） to the peak strain （εm） stood at σc/σm=0.62-0.89 and εc/εm=0.11-0.37, respectively. DRX could be observed during hot detormation process, microstructure evolution of the magnesium alloy at different temperatures and strain rates were studied with the aid of optical microscope（OM）, and the average recrystallized grain size was measured by means of intercepts on photomicrographs. It was shown that the average dynamically recrystallized grain size （drew） changed with different deformation parameters, the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of Zener-Hollomon parameter; the peak stress changed with the average recrystallized grain size, and the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of the peak stress.展开更多
The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The f...The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The flow stress-strain curves show the typical dynamic recrystallization with a peak,before reaching the steady state flow at higher deformation temperatures and lower strain rates. The constitutive equation governing the dynamic recrystallization( DRX) was obtained and the average activation energy of deformation was calculated as Q = 389. 5 kJ / mol by the regression analysis. The DRX grain size was also found to decrease with the increasing strain rate and the decreasing deformation temperature. The austenite grain size was refined from 118. 0 μm to 15. 07-40. 01 μm by DRX. The DRX grain size under diverse deformation conditions predicted by mathematical model agrees well with experimental results.展开更多
With hot rolling in laboratory and Gleeble thermal simulator, the hot working of a high nitrogen austenitic stainless steel （HNASS） was researched. The results showed that dynamic recovery （DRV） and dynamic recrys...With hot rolling in laboratory and Gleeble thermal simulator, the hot working of a high nitrogen austenitic stainless steel （HNASS） was researched. The results showed that dynamic recovery （DRV） and dynamic recrystalli- zation （DRX） in HNASS occurred during hot working, and both of them had well-defined stress peaks in flow curves under different conditions. During hot rolling experiment at temperature from 950 to 1 050 ℃, recrystallization phe- nomenon does not take place in test material until the deformation ratio is up to 40%. Recrystallization influences remarkably the strength and ductility of material, and the test HNASS possesses better combination of strength with ductility. According to the curve of θ--α （strain hardening rate-steady state stress）, the DRX critical strain of test material was determined. Also, the activation energy of hot working was calculated to be 746.5 kJ/mol and the equation of hot working was obtained.展开更多
基金Project (14JJ6047) supported by the Natural Science Foundation of Hunan Province,ChinaProject (51274092) supported by the National Natural Science Foundation of ChinaProject (20120161110040) supported by the Doctoral Program of Higher Education ofChina
文摘Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.
基金Special Project(2013) supported by China’s National Development and Reform Commission for R&D and Industrialization of New Materials
文摘In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of1000?1200°C and strain raterange of0.001?10s?1on a Gleeble?3800thermo-mechanical simulator.The results reveal that the flow stress is sensitive to the strainrate,and the dynamic recrystallization(DRX)is the principal softening mechanism.The strain rate of0.1s?1is considered to be thecritical point during the hot deformation at1000°C.The DRX process is closely related to the strain rate due to the adiabatictemperature rise.The strain rate has an important influence on DDRX and CDRX during hot deformation.The nucleation of DRXcan be activated by twin boundaries,and there is a lower fraction ofΣ3n(n=1,2,3)boundaries at the intermediate strain rate of0.1s?1.
基金supported by the National "Eleventh Five-Year Plan" Key Technologies R&D Program (2006BAE04B01)
文摘The characteristics of dynamic recrystallization （DRX） in Mg-Y-Nd-Gd-Zr-RE magnesium alloy were investigated by compression tests at temperatures between 523 and 723 K and at strain rates ranging from 0.002 to 1 s^-1 with maximum strain of 0.693. The strainhardening rate can be obtained from true stress-true strain curves, plots of θ-σ, -（δθ/δσ-）-a and lnθ-σ in different compression conditions were obtained by further study. The critical condition of the onset of DRX process was determined as （（δ/δσ（ δθ/δσ））=0. In the range of the above deformation temperature and strain rate, the ratio of critical stress （σc） to peak stress （σm） and critical strain （εc） to the peak strain （εm） stood at σc/σm=0.62-0.89 and εc/εm=0.11-0.37, respectively. DRX could be observed during hot detormation process, microstructure evolution of the magnesium alloy at different temperatures and strain rates were studied with the aid of optical microscope（OM）, and the average recrystallized grain size was measured by means of intercepts on photomicrographs. It was shown that the average dynamically recrystallized grain size （drew） changed with different deformation parameters, the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of Zener-Hollomon parameter; the peak stress changed with the average recrystallized grain size, and the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of the peak stress.
基金National Natural Science Foundation of China(No.51261009)
文摘The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The flow stress-strain curves show the typical dynamic recrystallization with a peak,before reaching the steady state flow at higher deformation temperatures and lower strain rates. The constitutive equation governing the dynamic recrystallization( DRX) was obtained and the average activation energy of deformation was calculated as Q = 389. 5 kJ / mol by the regression analysis. The DRX grain size was also found to decrease with the increasing strain rate and the decreasing deformation temperature. The austenite grain size was refined from 118. 0 μm to 15. 07-40. 01 μm by DRX. The DRX grain size under diverse deformation conditions predicted by mathematical model agrees well with experimental results.
基金Item Sponsored by National Basic Research Program of China(2004CB619103)
文摘With hot rolling in laboratory and Gleeble thermal simulator, the hot working of a high nitrogen austenitic stainless steel （HNASS） was researched. The results showed that dynamic recovery （DRV） and dynamic recrystalli- zation （DRX） in HNASS occurred during hot working, and both of them had well-defined stress peaks in flow curves under different conditions. During hot rolling experiment at temperature from 950 to 1 050 ℃, recrystallization phe- nomenon does not take place in test material until the deformation ratio is up to 40%. Recrystallization influences remarkably the strength and ductility of material, and the test HNASS possesses better combination of strength with ductility. According to the curve of θ--α （strain hardening rate-steady state stress）, the DRX critical strain of test material was determined. Also, the activation energy of hot working was calculated to be 746.5 kJ/mol and the equation of hot working was obtained.
