The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens ...The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.展开更多
Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in...Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.展开更多
The underlying mechanism of discontinuous yielding behavior in an ultrafine-grained(UFG)Fe-31 Mn-3 Al-3 Si(wt.%)austenitic TWIP steel was investigated by the use of advanced TEM technique with taking the plastic defor...The underlying mechanism of discontinuous yielding behavior in an ultrafine-grained(UFG)Fe-31 Mn-3 Al-3 Si(wt.%)austenitic TWIP steel was investigated by the use of advanced TEM technique with taking the plastic deformation mechanisms and their correlation with grains size near the macroscopic yield point into account.Typical yield drop mechanisms such as the dislocation locking by the Cottrell atmosphere due to the presence of interstitial impurities cannot explain the origin of this phenomenon in the UFG high-Mn austenitic TWIP steel.Here,we experimentally revealed that the plastic deformation mechanisms in the early stage of deformation,around the macroscopic yield point,show an obvious association with grain size.More specifically,the main mechanism shifts from the conventional slip in grain interior to twinning nucleated from grain boundaries with decreasing the grain size down to less than 1μm.Our observation indicates that the grain size dependent deformation mechanisms transition is also deeply associated with the discontinuous yielding behavior as it could govern the changes in the grain interior dislocation density of mobile dislocations around the macroscopic yield point.展开更多
In the present study,a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion(HPT)process under a pressure of 7.5 GPa up to 10 revolutions.Experimental results revealed that the microhardness of T...In the present study,a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion(HPT)process under a pressure of 7.5 GPa up to 10 revolutions.Experimental results revealed that the microhardness of Ti6Al4V was increased remarkably by about~41%and saturated at about 432 Hv after the HPT process.A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about52.7 nm was obtained eventually,and no obvious formation of metastableωphase was detected by XRD analysis.For the first time,the tribological properties of the HPT processed Ti6Al4V alloy were investigated by a ball-on-disc test at room temperature under a dry condition.It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy.With increasing the number of HPT revolutions,both friction coefficient and specific wear rate were obviously decreased due to the reduction of abrasion and adhesion wears.After being deformed by 10 HPT revolutions,the friction coefficient was reduced from about 0.49 to 0.37,and the specific wear rate was reduced by about 48%.The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.展开更多
The hetero-zone boundary affected region(HBAR)significantly influences the mechanical behaviors of layered materials,where the deformation mechanisms differ from those in the bulk layers.In this study,three kinds of h...The hetero-zone boundary affected region(HBAR)significantly influences the mechanical behaviors of layered materials,where the deformation mechanisms differ from those in the bulk layers.In this study,three kinds of heterogeneous Cu-Fe layered materials with different interface spacing but identical total thicknesses were prepared.The effects of HBAR and strain partitioning on the tensile behavior of the lay-ered materials were investigated.The results showed that layered materials had enhanced yield strength and uniform elongation with decreasing interface spacing.During tensile deformation,geometrically nec-essary dislocations(GNDs)were generated at hetero-zone boundaries and piled up near them,resulting in hetero-deformation induced(HDI)strengthening and HDI work hardening.Surface profilometry mea-surements showed that the Cu and Fe layers exhibited obvious strain partitioning and mutual constraint.With decreasing interface spacing,strain partitioning is enhanced by interlayer constraint,which pre-vented strain localization at interfaces and thus improved the synergetic deformation of layers.A higher fraction of HBAR can improve the mechanical performance of heterogeneous layered materials.This study deepens our understanding of the relationship between HBAR and strength-ductility synergy and provides some insight into the design of layered materials.展开更多
The so-called bimodal microstructure of Ti-6 Al-4 V alloy,composed of primaryαgrains(α_(p))and transformed β areas(β_(trans)),can be regarded as a"dual-phase"structure to some extent,the mechanical prope...The so-called bimodal microstructure of Ti-6 Al-4 V alloy,composed of primaryαgrains(α_(p))and transformed β areas(β_(trans)),can be regarded as a"dual-phase"structure to some extent,the mechanical properties of which are closely related to the sizes,volume fractions,distributions as well as nanohardness of the two constituents.In this study,the volume fractions of primaryαgrains(vol.%(α_(p)))were systematically modified in three series of bimodal microstructures with fixed primaryαgrain sizes(0.8μm,2.4μm and 5.0μm),by changing the intercritical annealing temperature(T_(int)).By evaluating the tensile properties at room temperature,it was found that with increasing T_(int)(decreasing vol.%(α_(p))),the yield strength of bimodal microstructures monotonically increased,while the uniform elongation firstly increased with T_(int)until 910°C and then drastically decreased afterwards,thereby dividing the T_(int)into two regions,namely region I(830-910°C)and region II(910-970℃).The detailed deformation behaviors within the two regions were studied and compared,from the perspectives of strain distribution analysis,slip system analysis as well as dislocation analysis.For bimodal microstructures in region I,due to the much lower nano-hardness ofβ_(trans)thanα_(p),there was a clear strain partitioning between the two constituents as well as a strain gradient from theα_(p)/β_(trans)interface to the grain interior ofα_(p).This activated a large number of geometrically necessary dislocations(GNDs)near the interface,mostly with components,which contributed greatly to the extraordinary work-hardening abilities of bimodal microstructures in region I.With increasing T_(int),theα_(p)/β_(trans)interface length density gradually increased and so was the density of GNDs with components,which explained the continuous increase of uniform elongation with T_(int)in this region.For bimodal microstructures in region II,where the nano-hardness ofβ_(trans)andα_(p)were comparable,neither a clear strain-partitioning tendency nor a strain gradient across theα_(p)/β_(trans)interface was observed.Consequently,only statistically stored dislocations(SSDs)with component were activated insideα_(p).The absence of dislocations together with a decreased volume fraction ofα_(p)resulted into a dramatic loss of uniform elongation for bimodal microstructures in region II.展开更多
Single-phase bcc-ferrite in an interstitial free(IF)steel was deformed to different strains in a wide range from low to high strains(ε=1–7)by torsion under different Zener-Hollomon(Z)conditions.The specimens were ra...Single-phase bcc-ferrite in an interstitial free(IF)steel was deformed to different strains in a wide range from low to high strains(ε=1–7)by torsion under different Zener-Hollomon(Z)conditions.The specimens were rapidly quenched after the torsion to preserve microstructures formed under different deformation conditions.The results showed that during high-Z(low-temperature)deformation,grains were subdivided by geometrically necessary boundaries(GNBs)via the grain subdivision mechanism.Deformation to high strains(ε>5)led to the ultrafine lamellar structures(with grain sizes<1μm)mainly composed of GNBs having high misorientation angles.Decreasing Z with increasing temperature and/or decreasing strain rate accelerated thermally activated processes,such as dynamic recovery and boundary migration.Unlike the ultrafine lamella formed under the high-Z condition,a variety of microstructures having equiaxed morphologies with fine to coarse grain sizes(>1μm)were realized with decreasing Z.The significance of the grain subdivision and the thermally activated phenomena on the formation of various microstructures under different deformation conditions is discussed.展开更多
The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensi...The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensile elongation was kept large(0.87→0.82).In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms.The initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip,with deformation-induced martensitic transformation(DIMT)also occurring in the later stage of deformation.Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain,which is attributed to the following effects.(i)Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the<111>//LD(LD:loading direction)austenite grains,which were the most stable grains for DIMT.As a result,most of the<111>//LD austenite grains in the UFG specimen failed to transform into martensite.(ii)Grain refinement also suppressed the autocatalytic effect of the martensitic transformation.Nevertheless,the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation.The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.展开更多
Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their ...Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their excellent thermal stability and high strength.Here we fabricated the supersaturated solid solution of Cu-20 at.%Fe,a typical immiscible alloy,in bulk state by high pressure torsion,which pro-vides a great freedom over powders for studying the microstructure evolution and mechanical properties in the process of the phase decomposition in immiscible alloys.We found that in the Cu-Fe solid solu-tion,spinodal decomposition of the Fe phases took place at the initial stage of annealing through volume diffusion.This process gives rise to:(1)metastableγ-Fe particles in the Cu grains with coherent Fe/Cu interface,and(2)the more stableα-Fe phase at the grain boundaries.This process was accompanied by moving boundary reaction which first proceeded in the pattern of spinodal decomposition and then changed into classical nucleation-growth mode with the depletion of Fe atoms in Cu.The resultant Cu-Fe nanocomposites were jointly strengthened by the ultrafine Cu andα-Fe grains according to the rule of mixture,including grain boundary strengthening and the hardening of nanoscaleγ-Fe precipitates in the Cu grains.The effects of different strengthening mechanisms were scrutinized and their contributions to mechanical properties were quantitatively evaluated.This work sheds light onto the opportunity of designing and fabricating nanostructured composites via phase decomposition in immiscible systems.展开更多
Previously,the in-plane mechanical anisotropy of Zr hot-rolled plates is ascribed mainly to the different activities of the deformation modes activated when loading along different directions.In this work,a quantitati...Previously,the in-plane mechanical anisotropy of Zr hot-rolled plates is ascribed mainly to the different activities of the deformation modes activated when loading along different directions.In this work,a quantitative study on the deformation behavior of a pure Zr hot-rolled plate under tension along the rolling direction(RD)and transverse direction(TD)reveals that both the activities of deformation modes and the anisotropy of grain boundary strengthening account for a tensile yield strength anisotropy along the TD and RD.Crystal plasticity simulations using viso-plastic self-consistent model show that prismatic slip is the predominant deformation mode for tension along the RD(RD-tension),while prismatic slip and basal slip are co-dominant deformation modes under tension along the TD(TD-tension).A low fraction of■under TD-tension,while hardly activated under RD-tension.The activation of basal slip with a much higher critical resolve shear stress under TD-tension contributes to a higher yield strength along the TD than along the RD.The grain boundary strengthening effect under tension along the TD and RD were compared by calculating the activation stress difference(△Stress)and the geometric compatibility factor(m′)between neighboring grains.The results indicate a higher grain boundary strengthening for TD-tension than that for RD-tension,which will lead to a higher yield strength along the TD.That is,the anisotropy of grain boundary strengthening between TD-tension and RD-tension also plays an important role in the in-plane anisotropy along the RD and TD.Afterward,the reasons for why there is a grain-boundary-strengthening anisotropy along the TD and RD were discussed.展开更多
基金supported by the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)the JSP EIG CONCERT-Japan(No.JPMJSC21C6)+5 种基金the Grant-in-Aid for Scientific Research on Innovative Area“High Entropy Alloys”(Nos.JP18H05455 and JP18H05451)the Grant-in-Aid for Scientific Re-search(A)(Nos.JP20H00306 and JP23H00234)the Grant-in-Aid for Research Activity Start-up(No.JP21K20487)the Grant-in-Aid for Early-Career Scientists(No.JP22K14501)the Grant-in-Aid for JSPS Research Fellow(No.JP18J20766)supported by China Scholarship Council(CSC),China.
文摘The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.
基金financially supported by the Elements Strategy Initiative for Structural Materials (ESISM, grant No. JPMXP0112101000) in Kyoto UniversityRXZ was supported by National Natural Science Foundation of China (NSFC, No. 51901007)+1 种基金SH and KA were supported by JSPS KAKENHI Nos. JP18H05479 and JP18H05476The neutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed under a project program (Project No. 2014P0102)。
文摘Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.
基金supported by NSF(ECCS 1542100,2025151)financial support by the JST CREST(JPMJCR1994)+2 种基金financial support by JSPS KAKENHI Grant Numbers(19H02029,20H02479)financial support by Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)the Grant-in-Aid for Scientific Research(S)(No.15H05767),the Grant-in-Aid for Scientific Research(A)(No.20H00306)。
文摘The underlying mechanism of discontinuous yielding behavior in an ultrafine-grained(UFG)Fe-31 Mn-3 Al-3 Si(wt.%)austenitic TWIP steel was investigated by the use of advanced TEM technique with taking the plastic deformation mechanisms and their correlation with grains size near the macroscopic yield point into account.Typical yield drop mechanisms such as the dislocation locking by the Cottrell atmosphere due to the presence of interstitial impurities cannot explain the origin of this phenomenon in the UFG high-Mn austenitic TWIP steel.Here,we experimentally revealed that the plastic deformation mechanisms in the early stage of deformation,around the macroscopic yield point,show an obvious association with grain size.More specifically,the main mechanism shifts from the conventional slip in grain interior to twinning nucleated from grain boundaries with decreasing the grain size down to less than 1μm.Our observation indicates that the grain size dependent deformation mechanisms transition is also deeply associated with the discontinuous yielding behavior as it could govern the changes in the grain interior dislocation density of mobile dislocations around the macroscopic yield point.
基金Australian Academy of Science(AAS)and Japan Society for the Promotion of Science(JSPS)for awarding him an international fellowship and financial supportAustralian Research Council(ARC)for awarding her the Discovery Early Career Researcher Award(DECRA)fellowship(grant no.DE180100124)+2 种基金the financial supports from the Cross-ministerial Strategic Innovation Promotion Program(SIP)from the Cabinet Office of Japanese government,the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)in Kyoto University from the Ministry of Education,Culture,Sports,Science and Technology(MEXT),JapanJST CREST(JPMJCR1994)from Japan Science and Technology Agency(JST)partly supported by Open Research Fund of State Key Laboratory of High Performance Complex Manufacturing,Central South University in China。
文摘In the present study,a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion(HPT)process under a pressure of 7.5 GPa up to 10 revolutions.Experimental results revealed that the microhardness of Ti6Al4V was increased remarkably by about~41%and saturated at about 432 Hv after the HPT process.A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about52.7 nm was obtained eventually,and no obvious formation of metastableωphase was detected by XRD analysis.For the first time,the tribological properties of the HPT processed Ti6Al4V alloy were investigated by a ball-on-disc test at room temperature under a dry condition.It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy.With increasing the number of HPT revolutions,both friction coefficient and specific wear rate were obviously decreased due to the reduction of abrasion and adhesion wears.After being deformed by 10 HPT revolutions,the friction coefficient was reduced from about 0.49 to 0.37,and the specific wear rate was reduced by about 48%.The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.
基金supported by the National Natural Science Foundation of China(Nos.51931003,92263201)the Fundamental Research Funds for the Central Universities(No.2022SCU12094)+2 种基金the Project funded by China Postdoctoral Science Foundation(No.2022M722253)supported by the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)the Grant-in-Aid for Scientific Research(A)(No.JP23H00234)through the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan.
文摘The hetero-zone boundary affected region(HBAR)significantly influences the mechanical behaviors of layered materials,where the deformation mechanisms differ from those in the bulk layers.In this study,three kinds of heterogeneous Cu-Fe layered materials with different interface spacing but identical total thicknesses were prepared.The effects of HBAR and strain partitioning on the tensile behavior of the lay-ered materials were investigated.The results showed that layered materials had enhanced yield strength and uniform elongation with decreasing interface spacing.During tensile deformation,geometrically nec-essary dislocations(GNDs)were generated at hetero-zone boundaries and piled up near them,resulting in hetero-deformation induced(HDI)strengthening and HDI work hardening.Surface profilometry mea-surements showed that the Cu and Fe layers exhibited obvious strain partitioning and mutual constraint.With decreasing interface spacing,strain partitioning is enhanced by interlayer constraint,which pre-vented strain localization at interfaces and thus improved the synergetic deformation of layers.A higher fraction of HBAR can improve the mechanical performance of heterogeneous layered materials.This study deepens our understanding of the relationship between HBAR and strength-ductility synergy and provides some insight into the design of layered materials.
基金financial support from Cross-ministerial Strategic Innovation Promotion Program(SIP)supported by the Cabinet Office of Japanese government and the Elements Strategy Initiative for Structural Materials(ESISM)in Kyoto University supported by the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japansupport by the Fundamental Research Funds for the Central Universities under grant No.N180204015。
文摘The so-called bimodal microstructure of Ti-6 Al-4 V alloy,composed of primaryαgrains(α_(p))and transformed β areas(β_(trans)),can be regarded as a"dual-phase"structure to some extent,the mechanical properties of which are closely related to the sizes,volume fractions,distributions as well as nanohardness of the two constituents.In this study,the volume fractions of primaryαgrains(vol.%(α_(p)))were systematically modified in three series of bimodal microstructures with fixed primaryαgrain sizes(0.8μm,2.4μm and 5.0μm),by changing the intercritical annealing temperature(T_(int)).By evaluating the tensile properties at room temperature,it was found that with increasing T_(int)(decreasing vol.%(α_(p))),the yield strength of bimodal microstructures monotonically increased,while the uniform elongation firstly increased with T_(int)until 910°C and then drastically decreased afterwards,thereby dividing the T_(int)into two regions,namely region I(830-910°C)and region II(910-970℃).The detailed deformation behaviors within the two regions were studied and compared,from the perspectives of strain distribution analysis,slip system analysis as well as dislocation analysis.For bimodal microstructures in region I,due to the much lower nano-hardness ofβ_(trans)thanα_(p),there was a clear strain partitioning between the two constituents as well as a strain gradient from theα_(p)/β_(trans)interface to the grain interior ofα_(p).This activated a large number of geometrically necessary dislocations(GNDs)near the interface,mostly with components,which contributed greatly to the extraordinary work-hardening abilities of bimodal microstructures in region I.With increasing T_(int),theα_(p)/β_(trans)interface length density gradually increased and so was the density of GNDs with components,which explained the continuous increase of uniform elongation with T_(int)in this region.For bimodal microstructures in region II,where the nano-hardness ofβ_(trans)andα_(p)were comparable,neither a clear strain-partitioning tendency nor a strain gradient across theα_(p)/β_(trans)interface was observed.Consequently,only statistically stored dislocations(SSDs)with component were activated insideα_(p).The absence of dislocations together with a decreased volume fraction ofα_(p)resulted into a dramatic loss of uniform elongation for bimodal microstructures in region II.
基金financially supported by the Grant-in-Aid for Scientific Research(S)(No.15H05767)the Grant-in-Aid for Scientific Research on Innovative Area,“Bulk Nanostructured Metals”(Area No.2201)+1 种基金the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)JST CREST(No.JPMJCR1994)all through the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan.
文摘Single-phase bcc-ferrite in an interstitial free(IF)steel was deformed to different strains in a wide range from low to high strains(ε=1–7)by torsion under different Zener-Hollomon(Z)conditions.The specimens were rapidly quenched after the torsion to preserve microstructures formed under different deformation conditions.The results showed that during high-Z(low-temperature)deformation,grains were subdivided by geometrically necessary boundaries(GNBs)via the grain subdivision mechanism.Deformation to high strains(ε>5)led to the ultrafine lamellar structures(with grain sizes<1μm)mainly composed of GNBs having high misorientation angles.Decreasing Z with increasing temperature and/or decreasing strain rate accelerated thermally activated processes,such as dynamic recovery and boundary migration.Unlike the ultrafine lamella formed under the high-Z condition,a variety of microstructures having equiaxed morphologies with fine to coarse grain sizes(>1μm)were realized with decreasing Z.The significance of the grain subdivision and the thermally activated phenomena on the formation of various microstructures under different deformation conditions is discussed.
基金financial support from the Japan Society for the Promotion of Science(No.JP18H05479)JST(Japan Science and Technology Agency)CREST(No.JPMJCR1994)+1 种基金the Grant-in-Aid for Scientific Research(Nos.JP20H00306 and JP22K18888)the Data Creation and Utilization Type Material Research and Development(No.JPMXP1122684766)。
文摘The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensile elongation was kept large(0.87→0.82).In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms.The initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip,with deformation-induced martensitic transformation(DIMT)also occurring in the later stage of deformation.Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain,which is attributed to the following effects.(i)Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the<111>//LD(LD:loading direction)austenite grains,which were the most stable grains for DIMT.As a result,most of the<111>//LD austenite grains in the UFG specimen failed to transform into martensite.(ii)Grain refinement also suppressed the autocatalytic effect of the martensitic transformation.Nevertheless,the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation.The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.
基金supported by the National Natural Science Foundation of China(No.51901007)the Fundamental Research Funds for the Central Universities+1 种基金NT was financially supported by JST CREST(JPMJCR1994)JSPS(Japan Society for the Promotion of Science)KAKENHI(Nos.20H00306,22K18888)all through the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan.
文摘Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their excellent thermal stability and high strength.Here we fabricated the supersaturated solid solution of Cu-20 at.%Fe,a typical immiscible alloy,in bulk state by high pressure torsion,which pro-vides a great freedom over powders for studying the microstructure evolution and mechanical properties in the process of the phase decomposition in immiscible alloys.We found that in the Cu-Fe solid solu-tion,spinodal decomposition of the Fe phases took place at the initial stage of annealing through volume diffusion.This process gives rise to:(1)metastableγ-Fe particles in the Cu grains with coherent Fe/Cu interface,and(2)the more stableα-Fe phase at the grain boundaries.This process was accompanied by moving boundary reaction which first proceeded in the pattern of spinodal decomposition and then changed into classical nucleation-growth mode with the depletion of Fe atoms in Cu.The resultant Cu-Fe nanocomposites were jointly strengthened by the ultrafine Cu andα-Fe grains according to the rule of mixture,including grain boundary strengthening and the hardening of nanoscaleγ-Fe precipitates in the Cu grains.The effects of different strengthening mechanisms were scrutinized and their contributions to mechanical properties were quantitatively evaluated.This work sheds light onto the opportunity of designing and fabricating nanostructured composites via phase decomposition in immiscible systems.
基金supported by the National Natural Science Foundation of China(No.52275161)the Ministry of Science and Technology High-End Intelligence Plan Team Project(No.G2022040015L)+2 种基金the Shaanxi Science and Technology Innovation Team(No.2023-CX-TD-50)the Shaanxi Qin Chuangyuan scientists and engineers’team(No.2022KXJ-145)the International Joint Research Center for Value-added Metallurgy and Processing of Non-ferrous Metals(No.2019SD0010).
文摘Previously,the in-plane mechanical anisotropy of Zr hot-rolled plates is ascribed mainly to the different activities of the deformation modes activated when loading along different directions.In this work,a quantitative study on the deformation behavior of a pure Zr hot-rolled plate under tension along the rolling direction(RD)and transverse direction(TD)reveals that both the activities of deformation modes and the anisotropy of grain boundary strengthening account for a tensile yield strength anisotropy along the TD and RD.Crystal plasticity simulations using viso-plastic self-consistent model show that prismatic slip is the predominant deformation mode for tension along the RD(RD-tension),while prismatic slip and basal slip are co-dominant deformation modes under tension along the TD(TD-tension).A low fraction of■under TD-tension,while hardly activated under RD-tension.The activation of basal slip with a much higher critical resolve shear stress under TD-tension contributes to a higher yield strength along the TD than along the RD.The grain boundary strengthening effect under tension along the TD and RD were compared by calculating the activation stress difference(△Stress)and the geometric compatibility factor(m′)between neighboring grains.The results indicate a higher grain boundary strengthening for TD-tension than that for RD-tension,which will lead to a higher yield strength along the TD.That is,the anisotropy of grain boundary strengthening between TD-tension and RD-tension also plays an important role in the in-plane anisotropy along the RD and TD.Afterward,the reasons for why there is a grain-boundary-strengthening anisotropy along the TD and RD were discussed.
