Fe-Cr ferritic/martensitic(F/M)steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies.In this study,a widely-used ferritic/martensitic steel,T91 steel,was irradiated by ...Fe-Cr ferritic/martensitic(F/M)steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies.In this study,a widely-used ferritic/martensitic steel,T91 steel,was irradiated by 196-MeV Kr^(+)ions at 550℃.To reveal the irradiation mechanism,the microstructure evolution of irradiated T91 steel was studied in details by transmission electron microscope(TEM).With increasing dose,the defects gradually changed from black dots to dislocation loops,and further to form dislocation walls near grain boundaries due to the production of a large number of dislocations.When many dislocation loops of primary a0/2<111>type with high migration interacted with other defects or carbon atoms,it led to the production of dislocation segments and other dislocation loops of a0<100>type.Lots of defects accumulated near grain boundaries in the irradiated area,especially in the high-dose area.The grain boundaries of martensite laths acted as important sinks of irradiation defects in T91.Elevated temperature facilitated the migration of defects,leading to the accumulation of defects near the grain boundaries of martensite laths.展开更多
Tilt probe penetrating friction stir welding(PFSW)was an innovative technology proposed in recent years to avoid the formation of kissing bond in the root of joint.However,with the heat input decreasing,"S"l...Tilt probe penetrating friction stir welding(PFSW)was an innovative technology proposed in recent years to avoid the formation of kissing bond in the root of joint.However,with the heat input decreasing,"S"line or zigzag line was easily introduced in the PFSW joint.In this study,ultrasonic enhanced tilt probe penetrating friction stir welding(U-PFSW)was developed to solve this problem and achieve improved joint mechanical properties.The experimental results confirmed that U-PFSW was a potent technology to completely clear the original butt surface,providing a crucial prerequisite for the achievement of highstrength joint.The application of ultrasonic improves the joint tensile strength and fracture elongation from 336 MPa and 4.3%to 359 MPa and 6.8%,respectively.Furthermore,the strength of stir zone was also increased from 391 MPa in PFSW to 420 MPa in U-PFSW.Analyses of texture and precipitate indicated that the dynamic recrystallization(DRX)and precipitation strengthening were both enhanced by the ultrasonic.Ultrasonic-enhanced DRX enabled a complete elimination of the"S"line;the enhanced precipitation strengthening by vacancy-induced mechanism in U-PFSW was the intrinsic reason for the significantly improved mechanical properties.展开更多
Achieving excellent strength-ductility synergy is a long-lasting research theme for structural materials.However,attempts to enhance strength usually induce a loss of ductility,i.e.,the strength-ductility trade-off.In...Achieving excellent strength-ductility synergy is a long-lasting research theme for structural materials.However,attempts to enhance strength usually induce a loss of ductility,i.e.,the strength-ductility trade-off.In the present study,the strength-ductility trade-off in duplex stainless steel(DSS)was overcome by developing a bimodal structure using friction stir processing(FSP).The ultimate tensile strength and elongation were improved by 140%and 109%,respectively,compared with those of the asreceived materials.Plastic deformation and concurrent dynamic recrystallization(DRX)during FSP were responsible for the formation of bimodal structure.Incompatible deformation resulted in the accumulation of dislocations at the phase boundaries,which triggered interpenetrating nucleation between the austenite and ferrite phases during DRX,leading to a bimodal structure.The in situ mechanical responses of the bimodal structure during tensile deformation were investigated by crystal plasticity finite element modeling(CPFEM).The stress field distribution obtained from CPFEM revealed that the simultaneous enhancement of strength and ductility in a bimodal structure could be attributed to the formation of a unique dispersion-strengthened system with the austenite and ferrite phases.It is indicated that the present design of alternating fine austenite and coarse ferrite layers is a promising strategy for optimizing the mechanical properties of DSSs.展开更多
Classical strength criteria are developed based on some empirical assumptions and have been widely used in engineering to predict material strength owing to their simplicity. In some cases, however, considerable discr...Classical strength criteria are developed based on some empirical assumptions and have been widely used in engineering to predict material strength owing to their simplicity. In some cases, however, considerable discrepancies arise between classicalstrength-criteria-based theoretical predictions and experimental results. Recently, a global nonequilibrium thermodynamics model has made important progress over classical models without resorting to any empirical assumptions. A prominent advance of this rational energy model is that it straightforwardly determines the dissipation energy density function, which is pertinent to inherent material ductility, through simple uniaxial and equi-biaxial tensions. In this study, a brief introduction of the nonequilibrium energy model was followed by systematic experimental investigation to determine the dissipation energy function and predict the material strength of pristine 316 L stainless steel-commonly used in engineering-under complex loadings. The results indicated that the strength contours predicted by the nonequilibrium energy criterion for complex loadings are consistent with the experimental results obtained for biaxial tension, implying that the nonequilibrium thermodynamics model is both reasonable and reliable. The prediction error was presumed to be induced by the anisotropy of the 316 L stainless steel sheets.展开更多
基金Project supported by Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302011)the National Natural Science Foundation of China(Grant Nos.U2032143,11902370,and 52005523)+2 种基金the International Science and Technology Cooperation Program of Guangdong Province,China(Grant No.2019A050510022)the China Postdoctoral Science Foundation(Grant Nos.2019M653173 and 2019TQ0374)the Heavy Ion Research Facility of Lanzhou(HIRFL).
文摘Fe-Cr ferritic/martensitic(F/M)steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies.In this study,a widely-used ferritic/martensitic steel,T91 steel,was irradiated by 196-MeV Kr^(+)ions at 550℃.To reveal the irradiation mechanism,the microstructure evolution of irradiated T91 steel was studied in details by transmission electron microscope(TEM).With increasing dose,the defects gradually changed from black dots to dislocation loops,and further to form dislocation walls near grain boundaries due to the production of a large number of dislocations.When many dislocation loops of primary a0/2<111>type with high migration interacted with other defects or carbon atoms,it led to the production of dislocation segments and other dislocation loops of a0<100>type.Lots of defects accumulated near grain boundaries in the irradiated area,especially in the high-dose area.The grain boundaries of martensite laths acted as important sinks of irradiation defects in T91.Elevated temperature facilitated the migration of defects,leading to the accumulation of defects near the grain boundaries of martensite laths.
基金the financial supports provided by the National Natural Science Foundation of China(No.52075122 and No.51775143)Key Research and Development Program of Guangdong Province(No.2019B090921003)+1 种基金China Postdoctoral Science Foundation(No.2020M683046)Defense Industrial Technology Development Program of China(No.JCKY2017203B066)。
文摘Tilt probe penetrating friction stir welding(PFSW)was an innovative technology proposed in recent years to avoid the formation of kissing bond in the root of joint.However,with the heat input decreasing,"S"line or zigzag line was easily introduced in the PFSW joint.In this study,ultrasonic enhanced tilt probe penetrating friction stir welding(U-PFSW)was developed to solve this problem and achieve improved joint mechanical properties.The experimental results confirmed that U-PFSW was a potent technology to completely clear the original butt surface,providing a crucial prerequisite for the achievement of highstrength joint.The application of ultrasonic improves the joint tensile strength and fracture elongation from 336 MPa and 4.3%to 359 MPa and 6.8%,respectively.Furthermore,the strength of stir zone was also increased from 391 MPa in PFSW to 420 MPa in U-PFSW.Analyses of texture and precipitate indicated that the dynamic recrystallization(DRX)and precipitation strengthening were both enhanced by the ultrasonic.Ultrasonic-enhanced DRX enabled a complete elimination of the"S"line;the enhanced precipitation strengthening by vacancy-induced mechanism in U-PFSW was the intrinsic reason for the significantly improved mechanical properties.
基金supported by the China Postdoctoral Science Foundation(Grant No.2020M683046)Guangdong Basic and Applied Basic Research Foundation(Grant No.2021A1515010536)+4 种基金State Key Laboratory of Solidification Processing in Northwestern Polytechnical University(NWPU)(Grant No.SKLSP202118)National Natural Science Foundation of China(Grant Nos.52105422,U2032143,11902370,51905112)Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302011)International Sci&Tech Cooperation Program of Guangdong Province(Grant No.2019A050510022)Key-Area Research and Development Program of Guangdong Province(Grant Nos.2019B010943001,2017B020235001)。
文摘Achieving excellent strength-ductility synergy is a long-lasting research theme for structural materials.However,attempts to enhance strength usually induce a loss of ductility,i.e.,the strength-ductility trade-off.In the present study,the strength-ductility trade-off in duplex stainless steel(DSS)was overcome by developing a bimodal structure using friction stir processing(FSP).The ultimate tensile strength and elongation were improved by 140%and 109%,respectively,compared with those of the asreceived materials.Plastic deformation and concurrent dynamic recrystallization(DRX)during FSP were responsible for the formation of bimodal structure.Incompatible deformation resulted in the accumulation of dislocations at the phase boundaries,which triggered interpenetrating nucleation between the austenite and ferrite phases during DRX,leading to a bimodal structure.The in situ mechanical responses of the bimodal structure during tensile deformation were investigated by crystal plasticity finite element modeling(CPFEM).The stress field distribution obtained from CPFEM revealed that the simultaneous enhancement of strength and ductility in a bimodal structure could be attributed to the formation of a unique dispersion-strengthened system with the austenite and ferrite phases.It is indicated that the present design of alternating fine austenite and coarse ferrite layers is a promising strategy for optimizing the mechanical properties of DSSs.
基金supported by the National Natural Science Foundation of China(Grant Nos.11832019,and 12002401)the NSFC Original Exploration Project(Grant No.12150001)+1 种基金the Project of Nuclear Power Technology Innovation Center of Science Technology and Industry for National Defense(Grant No.HDLCXZX-2021-HD-035)the Guangdong International Science and Technology Cooperation Program(Grant No.2020A0505020005)。
文摘Classical strength criteria are developed based on some empirical assumptions and have been widely used in engineering to predict material strength owing to their simplicity. In some cases, however, considerable discrepancies arise between classicalstrength-criteria-based theoretical predictions and experimental results. Recently, a global nonequilibrium thermodynamics model has made important progress over classical models without resorting to any empirical assumptions. A prominent advance of this rational energy model is that it straightforwardly determines the dissipation energy density function, which is pertinent to inherent material ductility, through simple uniaxial and equi-biaxial tensions. In this study, a brief introduction of the nonequilibrium energy model was followed by systematic experimental investigation to determine the dissipation energy function and predict the material strength of pristine 316 L stainless steel-commonly used in engineering-under complex loadings. The results indicated that the strength contours predicted by the nonequilibrium energy criterion for complex loadings are consistent with the experimental results obtained for biaxial tension, implying that the nonequilibrium thermodynamics model is both reasonable and reliable. The prediction error was presumed to be induced by the anisotropy of the 316 L stainless steel sheets.
