采用单道次热压缩实验在Gleeble-1500热力模拟机上研究了不同变形速率和变形温度下Hi-B钢的软化行为。结果表明,试验钢在较低应变速率下,主要以动态回复作为软化机制,在较高应变速率下,主要以动态再结晶作为软化机制。采用回归法计算出...采用单道次热压缩实验在Gleeble-1500热力模拟机上研究了不同变形速率和变形温度下Hi-B钢的软化行为。结果表明,试验钢在较低应变速率下,主要以动态回复作为软化机制,在较高应变速率下,主要以动态再结晶作为软化机制。采用回归法计算出动态回复的变形激活能和应变指数分别为287.12 k J/mol和4.88,由此建立了试验钢在低应变速率下的动态回复模型。展开更多
Mechanical behavior of nickel？titanium shape memory alloy（NiTi SMA） under hot deformation was investigated according to the true stress—strain curves of NiTi samples under compression at the strain rates of 0.001-...Mechanical behavior of nickel？titanium shape memory alloy（NiTi SMA） under hot deformation was investigated according to the true stress—strain curves of NiTi samples under compression at the strain rates of 0.001-1 s-1 and at the temperatures of 600？1000℃.Dynamic recovery and dynamic recrystallization of NiTi SMA were systematically investigated by microstructural evolution.The influence of the strain rates,the deformation temperatures and the deformation degree on the dynamic recovery and dynamic recrystallization of NiTi SMA was obtained as well.NiTi SMA was characterized by the combination of dynamic recovery and dynamic recrystallization at 600℃ and 700℃,but the complete dynamic recrystallization occurred at other deformation temperatures.Increasing the deformation temperatures or decreasing the stain rates leads to larger equiaxed grains.The deformation degree has an important influence on the dynamic recrystallization of NiTi SMA.There exists the critical deformation degree during the dynamic recrystallization of NiTi SMA,beyond which the larger deformation degree contributes to obtaining the finer equiaxed grains.展开更多
The microstructure and mechanical properties of 105 mm thick 5083 aluminum alloy hot rolled plate were investigated by metallurgical microscope, scanning electron microscope and tensile testing machine, and three majo...The microstructure and mechanical properties of 105 mm thick 5083 aluminum alloy hot rolled plate were investigated by metallurgical microscope, scanning electron microscope and tensile testing machine, and three major characteristic problems in mechanical properties inhomogeneity were explained. The results show that the mechanical properties of the rolled plate are inhomogeneous along the thickness direction. From the surface to the center, the strength shows an inverted "N" shape change and the elongation presents a semi "U" shape change. Several similar structural units composed of long fibrous grains(LFG) and short fibrous grains bands(SFGB) exist in a special layer(Layer 2) adjacent to the surface. This alternating layered distribution of LFG and SFGB is conducive to improving the plasticity by dispersing the plastic deformation concentrated on the boundary line(BL) between them. However, their different deformability will cause the alternation of additional stresses during the hot rolling, leading to the strength reduction. The closer the location to the center of the plate is, the more likely the recovery rather than the recrystallization occurs. This is the possible reason for the unnegligible difference in strength near the central region(Layer 4 and Layer 5).展开更多
Hot compression tests of 2050 Al-Li alloy were performed in the deformation temperature range of 340-500°C and strain rate range of 0.001-10 s-1 to investigate the hot deformation behavior of the alloy.The effect...Hot compression tests of 2050 Al-Li alloy were performed in the deformation temperature range of 340-500°C and strain rate range of 0.001-10 s-1 to investigate the hot deformation behavior of the alloy.The effects of friction and temperature difference on flow stress were analyzed and the flow curves were corrected.Based on the dynamic material model,processing map at a strain of 0.5 was established.The grain structure of the compressed samples was observed using optical microscopy.The results show that friction and temperature variation during the hot compression have significant influences on flow stress.The optimum processing domains are in the temperature range from 370 to 430°C with the strain rate range from 0.01 to 0.001 s-1,and in the temperature range from 440 to 500°C with the strain rate range from 0.3 to 0.01 s-1;the flow instable region is located at high strain rates(3-10 s-1)in the entire temperature range.Dynamic recovery(DRV)and dynamic recrystallization(DRX)are the main deformation mechanisms of the 2050 alloy in the stable domains,whereas the alloy exhibits flow localization in the instable region.展开更多
The constitutive model was developed to describe the relationship among flow stress,strain,strain rate,and deformation temperature completely,based on the characteristics of flow stress curves for a new kind of metast...The constitutive model was developed to describe the relationship among flow stress,strain,strain rate,and deformation temperature completely,based on the characteristics of flow stress curves for a new kind of metastable β Ti2448 titanium alloy from isothermal hot compression tests,in a wide range of temperatures（1023-1123 K） and strain rates（63-0.001 s-1）.During this process,the adopted hyperbolic sine function based on the unified viscoplasticity theory was used to model the flow behavior of alloy undergoing flow softening caused by dynamic recovery（DRV） at high strain rates（≥1 s-1）.The standard Avrami equation was adopted to represent the softening mechanism attributed to dynamic recrystallization（DRX） at low strain rates（1 s-1）.Additionally,the material constants were determined by optimization strategy,which is a new method to solve the nonlinear constitutive equation.The stress—strain curves predicted by the developed constitutive model agree well with the experimental results,which con-rms that the developed constitutive model can give an accurate estimate of the-ow stress of Ti2448 titanium alloy and provide an effective method to model the flow behavior of metastable β titanium alloys during hot deformation.展开更多
文摘采用单道次热压缩实验在Gleeble-1500热力模拟机上研究了不同变形速率和变形温度下Hi-B钢的软化行为。结果表明,试验钢在较低应变速率下,主要以动态回复作为软化机制,在较高应变速率下,主要以动态再结晶作为软化机制。采用回归法计算出动态回复的变形激活能和应变指数分别为287.12 k J/mol和4.88,由此建立了试验钢在低应变速率下的动态回复模型。
基金Project(51071056) supported by the National Natural Science Foundation of ChinaProjects(HEUCFR1132,HEUCF121712) supported by the Fundamental Research Funds for the Central Universities of China
文摘Mechanical behavior of nickel？titanium shape memory alloy（NiTi SMA） under hot deformation was investigated according to the true stress—strain curves of NiTi samples under compression at the strain rates of 0.001-1 s-1 and at the temperatures of 600？1000℃.Dynamic recovery and dynamic recrystallization of NiTi SMA were systematically investigated by microstructural evolution.The influence of the strain rates,the deformation temperatures and the deformation degree on the dynamic recovery and dynamic recrystallization of NiTi SMA was obtained as well.NiTi SMA was characterized by the combination of dynamic recovery and dynamic recrystallization at 600℃ and 700℃,but the complete dynamic recrystallization occurred at other deformation temperatures.Increasing the deformation temperatures or decreasing the stain rates leads to larger equiaxed grains.The deformation degree has an important influence on the dynamic recrystallization of NiTi SMA.There exists the critical deformation degree during the dynamic recrystallization of NiTi SMA,beyond which the larger deformation degree contributes to obtaining the finer equiaxed grains.
基金Project(2011DFR50950)supported by the International Science and Technology Cooperation Program of ChinaProject(51971183)supported by the National Natural Science Foundation of ChinaProject(cstc2019jcyj-msxmX0594)supported by the Natural Science Foundation of Chongqing,China。
文摘The microstructure and mechanical properties of 105 mm thick 5083 aluminum alloy hot rolled plate were investigated by metallurgical microscope, scanning electron microscope and tensile testing machine, and three major characteristic problems in mechanical properties inhomogeneity were explained. The results show that the mechanical properties of the rolled plate are inhomogeneous along the thickness direction. From the surface to the center, the strength shows an inverted "N" shape change and the elongation presents a semi "U" shape change. Several similar structural units composed of long fibrous grains(LFG) and short fibrous grains bands(SFGB) exist in a special layer(Layer 2) adjacent to the surface. This alternating layered distribution of LFG and SFGB is conducive to improving the plasticity by dispersing the plastic deformation concentrated on the boundary line(BL) between them. However, their different deformability will cause the alternation of additional stresses during the hot rolling, leading to the strength reduction. The closer the location to the center of the plate is, the more likely the recovery rather than the recrystallization occurs. This is the possible reason for the unnegligible difference in strength near the central region(Layer 4 and Layer 5).
基金Project(2013JSJJ0001)supported by the Teachers’ Research Fund,Central South University,ChinaProject supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,China
文摘Hot compression tests of 2050 Al-Li alloy were performed in the deformation temperature range of 340-500°C and strain rate range of 0.001-10 s-1 to investigate the hot deformation behavior of the alloy.The effects of friction and temperature difference on flow stress were analyzed and the flow curves were corrected.Based on the dynamic material model,processing map at a strain of 0.5 was established.The grain structure of the compressed samples was observed using optical microscopy.The results show that friction and temperature variation during the hot compression have significant influences on flow stress.The optimum processing domains are in the temperature range from 370 to 430°C with the strain rate range from 0.01 to 0.001 s-1,and in the temperature range from 440 to 500°C with the strain rate range from 0.3 to 0.01 s-1;the flow instable region is located at high strain rates(3-10 s-1)in the entire temperature range.Dynamic recovery(DRV)and dynamic recrystallization(DRX)are the main deformation mechanisms of the 2050 alloy in the stable domains,whereas the alloy exhibits flow localization in the instable region.
文摘The constitutive model was developed to describe the relationship among flow stress,strain,strain rate,and deformation temperature completely,based on the characteristics of flow stress curves for a new kind of metastable β Ti2448 titanium alloy from isothermal hot compression tests,in a wide range of temperatures（1023-1123 K） and strain rates（63-0.001 s-1）.During this process,the adopted hyperbolic sine function based on the unified viscoplasticity theory was used to model the flow behavior of alloy undergoing flow softening caused by dynamic recovery（DRV） at high strain rates（≥1 s-1）.The standard Avrami equation was adopted to represent the softening mechanism attributed to dynamic recrystallization（DRX） at low strain rates（1 s-1）.Additionally,the material constants were determined by optimization strategy,which is a new method to solve the nonlinear constitutive equation.The stress—strain curves predicted by the developed constitutive model agree well with the experimental results,which con-rms that the developed constitutive model can give an accurate estimate of the-ow stress of Ti2448 titanium alloy and provide an effective method to model the flow behavior of metastable β titanium alloys during hot deformation.
