Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientat...Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientation etc between two experiments were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and positron annihilation technique (PAT). The carbon concentration in matrix is more inhomogeneous in the experiment than that with γ→α→γ7 thermal history. The specific precipitation characteristic in the experiment without γ→α→γ thermal history is discussed on the basis of different carbon diffusion behavior and interaction between dislocation and excess carbon.展开更多
A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstruc...A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstructure observation showed that the grain size of EPTed samples was refined to about 1μm and the basal texture strength with maxima texture index was weakened to 7.18.EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects.Finally,uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time(30 s)at relatively low temperature(433 K).展开更多
The influence of orientation on the stress rupture behaviors of a 3 rd-generation nickel-based single-crystal superalloy was investigated at 1100℃/150 MPa.It is found that the stress rupture anisotropy is shown at 1...The influence of orientation on the stress rupture behaviors of a 3 rd-generation nickel-based single-crystal superalloy was investigated at 1100℃/150 MPa.It is found that the stress rupture anisotropy is shown at 1100℃,but not so obvious compared with that at intermediate temperatures.The [001] specimens display the longest rupture life,[111] specimens show the shortest rupture life,and [011] specimens exhibit the intermediate life.Detailed observations show that the final fracture is caused by crack initiation and propagation,and the anisotropy of three oriented specimens is related to the fracture modes,γ/γ’ microstructures,interfacial dislocation networks and cutting mechanisms in y’ phase.For [001] specimens,N-type rafted structures are formed which can well hinder the slip and climb of dislocations.Besides,the regular interfacial dislocation networks can prevent dislocations from cutting into y’ phase,leading to the improvement of the creep resistance.For [011] specimens,±45°rafted structures and irregular networks result in less strain hardening.For [111] specimens,a large number of crack propagation paths and inhomogeneous deformations caused by irregular rafted structures deteriorate the property and result in the shortest life.Furthermore,a[100] superdislocations with low mobility are widely formed in[001] and [011] specimens which suggests the low creep strain rate during steady creep stage,whereas superdislocations in[111] specimens possess high mobility,which indicates the high strain rate and corresponding poor stress rupture property.展开更多
A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Fur...A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mechanisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correlation of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.展开更多
In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble ...In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0.01-10.0 s 1 and temperatures of 1 050-1 140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization （DRX） depends sensitively on deformation temperature. When the temperature was lower than 1080 ~C, long and＂ narrow necklace grains were shown in the microstructure. When the temperature increased to 1 140 ℃, new recrystallization grains were genera-ted. The size and shape of X＇ precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the micro-structure observation, and the best material thermal processing temperature is above 1 128 ℃.展开更多
The microstructural evolution of rapidly solidified（RS） ZK60 powders extruded at 250 C was investigated.It was shown that formation of new ultrafine grains took place through continuous dynamic recrystallization（C...The microstructural evolution of rapidly solidified（RS） ZK60 powders extruded at 250 C was investigated.It was shown that formation of new ultrafine grains took place through continuous dynamic recrystallization（CDRX）,accompanied by the perfect bonding of powders via severe plastic deformation.At a low strain level,a well-defined structure made up of equiaxed and elongated subgrains was developed.Simultaneously,the operation of basal and non-basal dislocation slip led to the formation of low-angle dislocation cells（LADC） within the elongated subgrains.With increasing strain,the number and average misorientation of LADC increased,resulting in fragmentation of original elongation subgrains into a finally homogeneous fine-grained structure.Almost full-recrystallized structure with an average grain size of 0.4 μm was finally evolved after large cumulative strain.The results suggested that structural change was connected with thermal strain,where dislocation activities dominated this process.展开更多
Discrete dislocation plasticity(DDP)calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstr...Discrete dislocation plasticity(DDP)calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure.The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface,which can be quantitatively correlated to recent tribological experimental observations.Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads.展开更多
基金Authors acknowledge the financial support from the National Natural Science Foundation of China(No.50334010).
文摘Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientation etc between two experiments were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and positron annihilation technique (PAT). The carbon concentration in matrix is more inhomogeneous in the experiment than that with γ→α→γ7 thermal history. The specific precipitation characteristic in the experiment without γ→α→γ thermal history is discussed on the basis of different carbon diffusion behavior and interaction between dislocation and excess carbon.
基金supported financially by the National Natural Science Foundation of China(Nos.U1710118,U1810122,51504162 and 51601123)the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi(2018)+1 种基金the Natural Science Foundation of Shanxi Province(No.201801D221139)the Research Project Supported by Shanxi Scholarship Council of China(No.2016-029)。
文摘A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstructure observation showed that the grain size of EPTed samples was refined to about 1μm and the basal texture strength with maxima texture index was weakened to 7.18.EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects.Finally,uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time(30 s)at relatively low temperature(433 K).
基金financially supported by the National Natural Science Foundation of China (Nos. 51871210,51671196, 51631008 and 51771204)the National Key Research and Development Program of China (No. 2016YFB0701403).
文摘The influence of orientation on the stress rupture behaviors of a 3 rd-generation nickel-based single-crystal superalloy was investigated at 1100℃/150 MPa.It is found that the stress rupture anisotropy is shown at 1100℃,but not so obvious compared with that at intermediate temperatures.The [001] specimens display the longest rupture life,[111] specimens show the shortest rupture life,and [011] specimens exhibit the intermediate life.Detailed observations show that the final fracture is caused by crack initiation and propagation,and the anisotropy of three oriented specimens is related to the fracture modes,γ/γ’ microstructures,interfacial dislocation networks and cutting mechanisms in y’ phase.For [001] specimens,N-type rafted structures are formed which can well hinder the slip and climb of dislocations.Besides,the regular interfacial dislocation networks can prevent dislocations from cutting into y’ phase,leading to the improvement of the creep resistance.For [011] specimens,±45°rafted structures and irregular networks result in less strain hardening.For [111] specimens,a large number of crack propagation paths and inhomogeneous deformations caused by irregular rafted structures deteriorate the property and result in the shortest life.Furthermore,a[100] superdislocations with low mobility are widely formed in[001] and [011] specimens which suggests the low creep strain rate during steady creep stage,whereas superdislocations in[111] specimens possess high mobility,which indicates the high strain rate and corresponding poor stress rupture property.
基金This work was financially supported by the National Natural Science Foundation of China (No.50475144), the State Key Foundation-al Research Plan (No.G2000067206), and the Teaching and Research Award Fund for Outstanding Young Teachers in Higher Educa-tion Institutions of the Ministry of Education of China.
文摘A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mechanisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correlation of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.
基金Item Sponsored by National Natural Science Foundation of China ( 50974016 )
文摘In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0.01-10.0 s 1 and temperatures of 1 050-1 140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization （DRX） depends sensitively on deformation temperature. When the temperature was lower than 1080 ~C, long and＂ narrow necklace grains were shown in the microstructure. When the temperature increased to 1 140 ℃, new recrystallization grains were genera-ted. The size and shape of X＇ precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the micro-structure observation, and the best material thermal processing temperature is above 1 128 ℃.
基金National Natural Science Foundation of China(51371091,51174099,51001054)Scientific Research Project of Jiangsu University(15A368)Innovation Funds for Postgraduate of Jiangsu University(SJLX16_0445)
基金supported by the Doctoral Fundation of Jiangsu University (No.1281220014)the Graduate Independent Innovation Foundation of Shandong University (No.yzc09054)
文摘The microstructural evolution of rapidly solidified（RS） ZK60 powders extruded at 250 C was investigated.It was shown that formation of new ultrafine grains took place through continuous dynamic recrystallization（CDRX）,accompanied by the perfect bonding of powders via severe plastic deformation.At a low strain level,a well-defined structure made up of equiaxed and elongated subgrains was developed.Simultaneously,the operation of basal and non-basal dislocation slip led to the formation of low-angle dislocation cells（LADC） within the elongated subgrains.With increasing strain,the number and average misorientation of LADC increased,resulting in fragmentation of original elongation subgrains into a finally homogeneous fine-grained structure.Almost full-recrystallized structure with an average grain size of 0.4 μm was finally evolved after large cumulative strain.The results suggested that structural change was connected with thermal strain,where dislocation activities dominated this process.
基金This work was supported by the Engineering and Physical Sciences Research Council(EPSRC)(No.EP/N025954/1).
文摘Discrete dislocation plasticity(DDP)calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure.The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface,which can be quantitatively correlated to recent tribological experimental observations.Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads.
