The influence of grain size or grain refinement on the corrosion of Zr alloy is clarified by employing a series of electrochemical analyses and characterization techniques.The corrosion resistance,as a function of exp...The influence of grain size or grain refinement on the corrosion of Zr alloy is clarified by employing a series of electrochemical analyses and characterization techniques.The corrosion resistance,as a function of exposure time,F−concentration,and solution temperatures,of Zr alloys with different grain sizes is ascertained.The results confirm that refining the grain size can effectively enhance the short-time corrosion properties of Zr alloy in HNO_(3) with F−.The fine grained Zr alloy(~10μm in diameter)consistently exhibits a lower corrosion current density,ranging from 18%to 46%lower than that of the coarse-grained Zr alloy(~44μm).The enhanced corrosion resistance is attributed to the high density grain boundaries,which promote oxide stability,and accelerate the creation of the protective layer.The high corrosion rate and pseudo-passivation behavior of Zr alloys in fluorinated nitric acid originate from the accelerated“dissolution-passivation”of the oxide film.However,the grain refinement does not provide enduring anti-corrosion for Zr alloys.To meet the operation of spent fuel reprocessing,additional systematic efforts are required to evaluate the long term effect of grain refinement.展开更多
An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys dur...An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.展开更多
The reverse design of solid rocket motor(SRM)propellant grain involves determining the grain geometry to closely match a predefined internal ballistic curve.While existing reverse design methods are feasible,they ofte...The reverse design of solid rocket motor(SRM)propellant grain involves determining the grain geometry to closely match a predefined internal ballistic curve.While existing reverse design methods are feasible,they often face challenges such as lengthy computation times and limited accuracy.To achieve rapid and accurate matching between the targeted ballistic curve and complex grain shape,this paper proposes a novel reverse design method for SRM propellant grain based on time-series data imaging and convolutional neural network(CNN).First,a finocyl grain shape-internal ballistic curve dataset is created using parametric modeling techniques to comprehensively cover the design space.Next,the internal ballistic time-series data is encoded into three-channel images,establishing a potential relationship between the ballistic curves and their image representations.A CNN is then constructed and trained using these encoded images.Once trained,the model enables efficient inference of propellant grain dimensions from a target internal ballistic curve.This paper conducts comparative experiments across various neural network models,validating the effectiveness of the feature extraction method that transforms internal ballistic time-series data into images,as well as its generalization capability across different CNN architectures.Ignition tests were performed based on the predicted propellant grain.The results demonstrate that the relative error between the experimental internal ballistic curves and the target curves is less than 5%,confirming the validity and feasibility of the proposed reverse design methodology.展开更多
This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace appl...This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.展开更多
This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-...This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.展开更多
The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the...The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.展开更多
Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed ...Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness.The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffractometry(XRD).The formation mechanism of the gradient particles was discussed.The results show that after aging,a gradient distribution of large particles along the thickness is observed,the particles in the surface layer(SL) are distributed homogeneously,whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction,and the volume fraction of the particles in the SL is higher than that in the CL.Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL,which is the main reason for the formation of layered grain structure along the thickness in the sheets.展开更多
The influence of casting parameters on stray grain formation of a unidirectionally solidified superalloy IN738LC casting with three platforms was investigated by using a 3D cellular automaton-finite element （CAFE） m...The influence of casting parameters on stray grain formation of a unidirectionally solidified superalloy IN738LC casting with three platforms was investigated by using a 3D cellular automaton-finite element （CAFE） model in CALCOSOFT package. The model was first validated by comparison of the reported grain structure of AI-7%Si （mass fraction） alloy. Then, the influence of pouring temperature, heat flux of the lateral surface, convection heat coefficient of the cooled chill and mean undercooling of the bulk nucleation on the stray grain formation was studied during the unidirectional solidification. The predictions show that the stray grain formation is obviously sensitive to the pouring temperature, heat flux and mean undercooling of the bulk nucleation. However, increasing the heat convection coefficient has little influence on the stray grain formation.展开更多
Incipient motion of pebbles is an unsteady and random process,the main influence factors are pebble shape,non-uniformity,location in bed and flow condition.By virtue of the concept of the equivalent grain size,it is s...Incipient motion of pebbles is an unsteady and random process,the main influence factors are pebble shape,non-uniformity,location in bed and flow condition.By virtue of the concept of the equivalent grain size,it is shown that d_ηfollows a normal distribution following a regression analysis of measured data.Consid- ering the influence of pebble shape and the relative exposure degree,formula of calculating the incipient veloc- ity for pebbles is deduced based on the equivalent grain size of pebble and the...展开更多
基金Project(U2067217)supported by the National Natural Science Foundation of ChinaProject(SASTIND)supported by the State Administration of Science,Technology and Industry for National Defense,ChinaProject(2020M683572)supported by China Postdoctoral Science Foundation。
文摘The influence of grain size or grain refinement on the corrosion of Zr alloy is clarified by employing a series of electrochemical analyses and characterization techniques.The corrosion resistance,as a function of exposure time,F−concentration,and solution temperatures,of Zr alloys with different grain sizes is ascertained.The results confirm that refining the grain size can effectively enhance the short-time corrosion properties of Zr alloy in HNO_(3) with F−.The fine grained Zr alloy(~10μm in diameter)consistently exhibits a lower corrosion current density,ranging from 18%to 46%lower than that of the coarse-grained Zr alloy(~44μm).The enhanced corrosion resistance is attributed to the high density grain boundaries,which promote oxide stability,and accelerate the creation of the protective layer.The high corrosion rate and pseudo-passivation behavior of Zr alloys in fluorinated nitric acid originate from the accelerated“dissolution-passivation”of the oxide film.However,the grain refinement does not provide enduring anti-corrosion for Zr alloys.To meet the operation of spent fuel reprocessing,additional systematic efforts are required to evaluate the long term effect of grain refinement.
基金Project(2021YFB3701103) supported by the National Key R&D Program of China。
文摘An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.
文摘The reverse design of solid rocket motor(SRM)propellant grain involves determining the grain geometry to closely match a predefined internal ballistic curve.While existing reverse design methods are feasible,they often face challenges such as lengthy computation times and limited accuracy.To achieve rapid and accurate matching between the targeted ballistic curve and complex grain shape,this paper proposes a novel reverse design method for SRM propellant grain based on time-series data imaging and convolutional neural network(CNN).First,a finocyl grain shape-internal ballistic curve dataset is created using parametric modeling techniques to comprehensively cover the design space.Next,the internal ballistic time-series data is encoded into three-channel images,establishing a potential relationship between the ballistic curves and their image representations.A CNN is then constructed and trained using these encoded images.Once trained,the model enables efficient inference of propellant grain dimensions from a target internal ballistic curve.This paper conducts comparative experiments across various neural network models,validating the effectiveness of the feature extraction method that transforms internal ballistic time-series data into images,as well as its generalization capability across different CNN architectures.Ignition tests were performed based on the predicted propellant grain.The results demonstrate that the relative error between the experimental internal ballistic curves and the target curves is less than 5%,confirming the validity and feasibility of the proposed reverse design methodology.
基金Project(2021GK1040) supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProjects(52375398,52171018) supported by the National Natural Science Foundation of China+1 种基金Project(Kfkt2023-09) supported by the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(E2021203059) supported by the Natural Science Foundation of Hebei Province,China。
文摘This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.
文摘This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.
基金Project(2023YFC2907403)supported by the National Key R&D Program of ChinaProject(52074021)supported by the National Natural Science Foundation of China+1 种基金Project(2242045)supported by Beijing Natural Science Foundation,ChinaProject(ZD202216)supported by the Beijing Association of Higher Education,China。
文摘The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.
基金Project(2006DFA53250) supported by the International Science and Technology Cooperation Program of ChinaProject(2005CB623706) supported by the Major State Basic Research Development Program of China
文摘Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness.The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffractometry(XRD).The formation mechanism of the gradient particles was discussed.The results show that after aging,a gradient distribution of large particles along the thickness is observed,the particles in the surface layer(SL) are distributed homogeneously,whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction,and the volume fraction of the particles in the SL is higher than that in the CL.Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL,which is the main reason for the formation of layered grain structure along the thickness in the sheets.
基金Project(08BZ1130100) supported by the Science and Technology Committee of Shanghai,ChinaProject(SHUCX102251) supported by the Innovation Fund for Graduate Student of Shanghai University,China
文摘The influence of casting parameters on stray grain formation of a unidirectionally solidified superalloy IN738LC casting with three platforms was investigated by using a 3D cellular automaton-finite element （CAFE） model in CALCOSOFT package. The model was first validated by comparison of the reported grain structure of AI-7%Si （mass fraction） alloy. Then, the influence of pouring temperature, heat flux of the lateral surface, convection heat coefficient of the cooled chill and mean undercooling of the bulk nucleation on the stray grain formation was studied during the unidirectional solidification. The predictions show that the stray grain formation is obviously sensitive to the pouring temperature, heat flux and mean undercooling of the bulk nucleation. However, increasing the heat convection coefficient has little influence on the stray grain formation.
基金Supported by 973 Program(2003CB415202)the Doctoral Course Founadtion of Higher Education of China(20020610098).
文摘Incipient motion of pebbles is an unsteady and random process,the main influence factors are pebble shape,non-uniformity,location in bed and flow condition.By virtue of the concept of the equivalent grain size,it is shown that d_ηfollows a normal distribution following a regression analysis of measured data.Consid- ering the influence of pebble shape and the relative exposure degree,formula of calculating the incipient veloc- ity for pebbles is deduced based on the equivalent grain size of pebble and the...
