The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50...The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.展开更多
The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map...The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map, transmission electron microscopy and electron backscatter diffraction analysis. The results show that the peak stress decreases with increasing deformation temperatures and decreasing strain rate. The average deformation activation energy is 185 kJ/mol in the parameter range investigated. The flow stress model was constructed. The main softening mechanism is dynamic recovery. The processing map was obtained using dynamic material model, and the suggested processing window is 400-440℃ and 0.001-0.1 s^-1.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 Al?4.10Cu?1.42Mg?0.57Mn?0.12Zr alloy was compressed to different strains at deformation temperature of 300 oC and strain rate of 10 s?1 on Gleeble?1500 system. The dynamic complex microstructures evolutions were i...The Al?4.10Cu?1.42Mg?0.57Mn?0.12Zr alloy was compressed to different strains at deformation temperature of 300 oC and strain rate of 10 s?1 on Gleeble?1500 system. The dynamic complex microstructures evolutions were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The true stress?true strain curves exhibited a peak stress at critical strain, after which the flow stresses decreased monotonically, showing a dynamic flow softening. As the strain increased, the dislocation tangled to cell structure and sub-grain structure, which indicated the occurrence of dynamic recovery during deformation. Dynamic precipitations ofS (Al2CuMg),θ (Al2Cu) and Al3Zr phase were accelerated and coarsened by deformation. ContinuousS phases precipitated in the Al matrix and discontinuousS phases were found to be nucleated near the Al3Zr phase and at the sub-grain boundary. The flow softening mechanism was resulted from the reduction of dislocation density which attributed to dynamic recovery and precipitates coarsening.展开更多
Al-cladded Al-Zn-Mg-Cu sheets were compressed up to70%reduction on a Gleeble-3500thermo-mechanical simulatorwith temperatures ranging from380to450°C at strain rates between0.1and30s-1.The microstructures of the A...Al-cladded Al-Zn-Mg-Cu sheets were compressed up to70%reduction on a Gleeble-3500thermo-mechanical simulatorwith temperatures ranging from380to450°C at strain rates between0.1and30s-1.The microstructures of the Al cladding and theAl-Zn-Mg-Cu matrix were characterized by electron back-scattered diffraction(EBSD)and X-ray diffraction(XRD).Themicrostructure is closely related to the level of recovery and recrystallization,which can be influenced by deformation temperature,deformation pass and deformation rate.The level of recovery and recrystallization are different in the Al cladding and theAl-Zn-Mg-Cu matrix.Higher deformation temperature results in higher degree of recrystallization and coarser grain size.Staticrecrystallization and recovery can happen during the interval of deformation passes.Higher strain rate leads to finer sub-grains atstrain rate below10s-1;however,dynamic recovery and recrystallization are limited at strain rate of30s-1due to shorter duration atelevated temperatures.展开更多
Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating w...Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating was studied. As-deformed alloy was characterized by quasi-amorphous single-phase β condition with an abnormal temperature dependence of electric resistance that was normalized after 48 h exposure at room temperature as a result of isothermal ω phase precipitation. Subsequent rapid heating with a rate of 5 ℃/s caused recovery and recrystallization. Tensile properties of the alloy after different treatments were determined and discussed.展开更多
The hot deformation behavior of Pt−10Ir alloy was studied under a wide range of deformation parameters.At a low deformation temperature(950−1150℃),the softening mechanism is primarily dynamic recovery.In addition,dyn...The hot deformation behavior of Pt−10Ir alloy was studied under a wide range of deformation parameters.At a low deformation temperature(950−1150℃),the softening mechanism is primarily dynamic recovery.In addition,dynamic recrystallization by progressive lattice rotation near grain boundaries(DRX by LRGBs)and microshear bands assisted dynamic recrystallization(MSBs assisted DRX)coordinate the deformation.However,it is difficult for the dynamic softening to offset the stain hardening due to a limited amount of DRXed grains.At a high deformation temperature(1250−1350℃),three main DRX mechanisms associated with strain rates occur:DRX by LRGBs,DRX by a homogeneous increase in misorientation(HIM)and geometric DRX(GDRX).With increasing strain,DRX by LRGBs is enhanced gradually under high strain rates;the“pinch-off”effect is enhanced at low strain rates,which was conducive to the formation of a uniform and fine microstructure.展开更多
Ceramic fiber reinforced silica aerogel composites are novel insulation materials in the thermal protection field for hypersonic vehicles. Before the aerogel composites are applied in load-bearing structures, it is ne...Ceramic fiber reinforced silica aerogel composites are novel insulation materials in the thermal protection field for hypersonic vehicles. Before the aerogel composites are applied in load-bearing structures, it is necessary to investigate their mechanical properties including load-bearing and deformation recovery capabilities. High temperature from service conditions will have important effects on the mechanical properties of thermal protection materials. In this paper, compression tests including loading and unloading stages were conducted for ceramic fiber reinforced silica aerogel composites at room temperature and elevated temperatures(300℃, 600℃ and 900℃). Influences of thermal exposure to high temperature and high temperature service environment on the compression property and deformation recovery were both investigated. Scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FT-IR) and X-ray diffraction(XRD) were applied to help understand the mechanisms of mechanical property variations. The experimental results show that the compression modulus and strength both increase with the increasing thermal exposure temperature and testing temperature,but the deformation recovery capability decreases. The micro structure changes caused by thermal sintering are considered as the main reason for the property variations.Viscous flow and matter transport due to high temperature resulted in the fusion of aerogel particles. This made the particle skeleton thicker and stronger, which led to higher stiffness and strength of the composites. However, matrix cracks induced by the formation and fracture of larger pores made unrecoverable deformation more serious. In the tests at elevated temperatures,the aggregation of aerogel particles in a fused state got more severe because of the addition of mechanical load. As a result, the degradation of deformation recovery capability became more significant.展开更多
After their experimental data were re-explained in terms of the maximum-effective-moment （MEM） criterion, Gomez-Rivas and Griera （2015） challenge the validity of the MEM-Criterion in terms of shear fractures, whic...After their experimental data were re-explained in terms of the maximum-effective-moment （MEM） criterion, Gomez-Rivas and Griera （2015） challenge the validity of the MEM-Criterion in terms of shear fractures, which have mixed up with shear fractures and shear bands. The two features are similar in appearance but different in deformation mechanism （s）. The MEM-criterion proves that ±55° to σ1era are the maximum effective moment directions and the shear bands that formed by mate- rial-line （beddings or fabrics） rotation mechanism have a constant conjugate angle of 110°. Theoretically, the 55° or 110° is a material-invariant, and practically, a statistic-invariant or preferred direction with average deviation of -10°. By this angle, shear bands can be easily recognized from shear fractures with conjugate angle never over 90°. The High-strain deformation in the lozenges usually predates the surrounding shear bands. Two stress states can not coexisted simultaneously in the same place and the resolving cr1＇ normal to the related shear zone represents 0-100% deformation partitioning, depending on the original kinematic vorticity of the shear zones.展开更多
基金Project(51075132)supported by the National Natural Science Foundation of ChinaProject(20090161110027)supported by the Doctoral Fund of Ministry of Education of ChinaProject(2011BAG03B02)supported by National Key Technology R&D Program during the 12th Five-Year Plan Period,China
文摘The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.
文摘The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map, transmission electron microscopy and electron backscatter diffraction analysis. The results show that the peak stress decreases with increasing deformation temperatures and decreasing strain rate. The average deformation activation energy is 185 kJ/mol in the parameter range investigated. The flow stress model was constructed. The main softening mechanism is dynamic recovery. The processing map was obtained using dynamic material model, and the suggested processing window is 400-440℃ and 0.001-0.1 s^-1.
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(2009CB623704)supported by the National Basic Research(973)Program of ChinaProject(20130161110007)supported by the Doctoral Program of the Ministry of Education,ChinaProject(CX2013B128)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘The Al?4.10Cu?1.42Mg?0.57Mn?0.12Zr alloy was compressed to different strains at deformation temperature of 300 oC and strain rate of 10 s?1 on Gleeble?1500 system. The dynamic complex microstructures evolutions were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The true stress?true strain curves exhibited a peak stress at critical strain, after which the flow stresses decreased monotonically, showing a dynamic flow softening. As the strain increased, the dislocation tangled to cell structure and sub-grain structure, which indicated the occurrence of dynamic recovery during deformation. Dynamic precipitations ofS (Al2CuMg),θ (Al2Cu) and Al3Zr phase were accelerated and coarsened by deformation. ContinuousS phases precipitated in the Al matrix and discontinuousS phases were found to be nucleated near the Al3Zr phase and at the sub-grain boundary. The flow softening mechanism was resulted from the reduction of dislocation density which attributed to dynamic recovery and precipitates coarsening.
基金Projects(2016YFB0300901,2016YFB0700401) supported by the National Key Research and Development Program of ChinaProjects(106112015CDJXY130003,106112015CDJXZ138803) supported by the Fundamental Research Funds for the Central Universities,China
文摘Al-cladded Al-Zn-Mg-Cu sheets were compressed up to70%reduction on a Gleeble-3500thermo-mechanical simulatorwith temperatures ranging from380to450°C at strain rates between0.1and30s-1.The microstructures of the Al cladding and theAl-Zn-Mg-Cu matrix were characterized by electron back-scattered diffraction(EBSD)and X-ray diffraction(XRD).Themicrostructure is closely related to the level of recovery and recrystallization,which can be influenced by deformation temperature,deformation pass and deformation rate.The level of recovery and recrystallization are different in the Al cladding and theAl-Zn-Mg-Cu matrix.Higher deformation temperature results in higher degree of recrystallization and coarser grain size.Staticrecrystallization and recovery can happen during the interval of deformation passes.Higher strain rate leads to finer sub-grains atstrain rate below10s-1;however,dynamic recovery and recrystallization are limited at strain rate of30s-1due to shorter duration atelevated temperatures.
文摘Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating was studied. As-deformed alloy was characterized by quasi-amorphous single-phase β condition with an abnormal temperature dependence of electric resistance that was normalized after 48 h exposure at room temperature as a result of isothermal ω phase precipitation. Subsequent rapid heating with a rate of 5 ℃/s caused recovery and recrystallization. Tensile properties of the alloy after different treatments were determined and discussed.
基金financial supports from the National Natural Science Foundation of China(Nos.52161023,51901204)Science and Technology Project of Yunnan Precious Metal Laboratory,China(No.YPML-2023050208)+1 种基金Yunnan Science and Technology Planning Project,China(Nos.202201AU070010,202301AT070276,202302AB080008,202303AA080001)Postgraduate Research and Innovation Foundation of Yunnan University,China(No.2021Y338).
文摘The hot deformation behavior of Pt−10Ir alloy was studied under a wide range of deformation parameters.At a low deformation temperature(950−1150℃),the softening mechanism is primarily dynamic recovery.In addition,dynamic recrystallization by progressive lattice rotation near grain boundaries(DRX by LRGBs)and microshear bands assisted dynamic recrystallization(MSBs assisted DRX)coordinate the deformation.However,it is difficult for the dynamic softening to offset the stain hardening due to a limited amount of DRXed grains.At a high deformation temperature(1250−1350℃),three main DRX mechanisms associated with strain rates occur:DRX by LRGBs,DRX by a homogeneous increase in misorientation(HIM)and geometric DRX(GDRX).With increasing strain,DRX by LRGBs is enhanced gradually under high strain rates;the“pinch-off”effect is enhanced at low strain rates,which was conducive to the formation of a uniform and fine microstructure.
基金supported by the National Natural Science Foundation of China(Grant No.51275023)
文摘Ceramic fiber reinforced silica aerogel composites are novel insulation materials in the thermal protection field for hypersonic vehicles. Before the aerogel composites are applied in load-bearing structures, it is necessary to investigate their mechanical properties including load-bearing and deformation recovery capabilities. High temperature from service conditions will have important effects on the mechanical properties of thermal protection materials. In this paper, compression tests including loading and unloading stages were conducted for ceramic fiber reinforced silica aerogel composites at room temperature and elevated temperatures(300℃, 600℃ and 900℃). Influences of thermal exposure to high temperature and high temperature service environment on the compression property and deformation recovery were both investigated. Scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FT-IR) and X-ray diffraction(XRD) were applied to help understand the mechanisms of mechanical property variations. The experimental results show that the compression modulus and strength both increase with the increasing thermal exposure temperature and testing temperature,but the deformation recovery capability decreases. The micro structure changes caused by thermal sintering are considered as the main reason for the property variations.Viscous flow and matter transport due to high temperature resulted in the fusion of aerogel particles. This made the particle skeleton thicker and stronger, which led to higher stiffness and strength of the composites. However, matrix cracks induced by the formation and fracture of larger pores made unrecoverable deformation more serious. In the tests at elevated temperatures,the aggregation of aerogel particles in a fused state got more severe because of the addition of mechanical load. As a result, the degradation of deformation recovery capability became more significant.
基金supported financially by the Project from Geological Survey of China(Grant No.12120115027101)
文摘After their experimental data were re-explained in terms of the maximum-effective-moment （MEM） criterion, Gomez-Rivas and Griera （2015） challenge the validity of the MEM-Criterion in terms of shear fractures, which have mixed up with shear fractures and shear bands. The two features are similar in appearance but different in deformation mechanism （s）. The MEM-criterion proves that ±55° to σ1era are the maximum effective moment directions and the shear bands that formed by mate- rial-line （beddings or fabrics） rotation mechanism have a constant conjugate angle of 110°. Theoretically, the 55° or 110° is a material-invariant, and practically, a statistic-invariant or preferred direction with average deviation of -10°. By this angle, shear bands can be easily recognized from shear fractures with conjugate angle never over 90°. The High-strain deformation in the lozenges usually predates the surrounding shear bands. Two stress states can not coexisted simultaneously in the same place and the resolving cr1＇ normal to the related shear zone represents 0-100% deformation partitioning, depending on the original kinematic vorticity of the shear zones.
