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
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 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
Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a...Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.展开更多
Refractory high entropy alloys feature outstanding properties making them a promising materials class for next-generation hightemperature applications.At high temperatures,materials properties are strongly affected by...Refractory high entropy alloys feature outstanding properties making them a promising materials class for next-generation hightemperature applications.At high temperatures,materials properties are strongly affected by lattice vibrations(phonons).Phonons critically influence thermal stability,thermodynamic and elastic properties,as well as thermal conductivity.In contrast to perfect crystals and ordered alloys,the inherently present mass and force constant fluctuations in multi-component random alloys(high entropy alloys)can induce significant phonon scattering and broadening.Despite their importance,phonon scattering and broadening have so far only scarcely been investigated for high entropy alloys.We tackle this challenge from a theoretical perspective and employ ab initio calculations to systematically study the impact of force constant and mass fluctuations on the phonon spectral functions of 12 body-centered cubic random alloys,from binaries up to 5-component high entropy alloys,addressing the key question of how chemical complexity impacts phonons.We find that it is crucial to include both mass and force constant fluctuations.If one or the other is neglected,qualitatively wrong results can be obtained such as artificial phonon band gaps.We analyze how the results obtained for the phonons translate into thermodynamically integrated quantities,specifically the vibrational entropy.Changes in the vibrational entropy with increasing the number of elements can be as large as changes in the configurational entropy and are thus important for phase stability considerations.The set of studied alloys includes MoTa,MoTaNb,MoTaNbW,MoTaNbWV,VW,VWNb,VWTa,VWNbTa,VTaNbTi,VWNbTaTi,HfZrNb,HfMoTaTiZr.展开更多
Rejuvenation is the structural excitation of glassy materials,and is a promising approach for improving the macroscopic deformability of metallic glasses.This atomistic study proposes the application of compressive hy...Rejuvenation is the structural excitation of glassy materials,and is a promising approach for improving the macroscopic deformability of metallic glasses.This atomistic study proposes the application of compressive hydrostatic pressure during the glass-forming quenching process and demonstrates highly rejuvenated glass states that have not been attainable without the application of pressure.Surprisingly,the pressure-promoted rejuvenation process increases the characteristic short-and mediumrange order,even though it leads to a higher-energy glassy state.This‘local order’–‘energy’relation is completely opposite to conventional thinking regarding the relation,suggesting the presence of a well-ordered high-pressure glass/high-energy glass phase.We also demonstrate that the rejuvenated glass made by the pressure-promoted rejuvenation exhibits greater plastic performance than as-quenched glass,and greater strength and stiffness than glass made without the application of pressure.It is thus possible to tune the mechanical properties of glass using the pressure-promoted rejuvenation technique.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
A first-principles-based computational tool for simulating phonons of magnetic random solid solutions including thermal magnetic fluctuations is developed.The method takes fluctuations of force constants due to magnet...A first-principles-based computational tool for simulating phonons of magnetic random solid solutions including thermal magnetic fluctuations is developed.The method takes fluctuations of force constants due to magnetic excitations as well as due to chemical disorder into account.The developed approach correctly predicts the experimentally observed unusual phonon hardening of a transverse acoustic mode in Fe–Pd an Fe–Pt Invar alloys with increasing temperature.This peculiar behavior,which cannot be explained within a conventional harmonic picture,turns out to be a consequence of thermal magnetic fluctuations.The proposed methodology can be straightforwardly applied to a wide range of materials to reveal new insights into physical behaviors and to design materials through computation,which were not accessible so far.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 physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method,molecular dy...The physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method,molecular dynamics simulation,etc,applied to homogeneous and heterogeneous systems.Firstly,we examined the elastic properties based on electronic structure calculations in a homogeneous system and attributed the physical origin of the loss of ductility with increasing Si content to the combined effects of magneto-volume and D03 ordering.As a typical example of a heterogeneity forming a microstructure,we focus on grain boundaries,and segregation behavior of Si atoms is studied through high-precision electronic structure calculations.Two kinds of segregation sites are identified:looser and tighter sites.Depending on the site,different segregation mechanisms are revealed.Finally,the dislocation behavior in the Fe-Si alloy is investigated mainly by molecular dynamics simulations combined with electronic structure calculations.The solid-solution hardening and softening are interpreted in terms of two kinds of energy barriers for kink nucleation and migration on a screw dislocation line.Furthermore,the clue to the peculiar work hardening behavior is discussed based on kinetic Monte Carlo simulations by focusing on the preferential selection of slip planes triggered by kink nucleation.展开更多
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supported financially by the Fundamental Research Funds for the Central Universities(No.N180204015)supported by Chinese Academy of Sciences(CAS)and Japan Society for the Promotion of Science(JSPS)through the Bilateral Program(No.GJHZ1774)supported by Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan,through the Elements Strategy Initiative for Structural Materials(ESISM)Project and the Grant-in-Aid for Scientific Research(S)(No.15H05767)。
文摘Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.
基金Funding by the Deutsche Forschungsgemeinschaft(DFG)through the scholarship KO 5080/1-1by the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(Grant agreement No.639211)+1 种基金by the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan,through the Elements Strategy Initiative for Structural Materials(ESISM)of Kyoto Universityby the Japan Society for the Promotion of Science(JSPS)KAKENHI Grant-in-Aid for Young Scientist(B)(Grant No.16K18228)are gratefully acknowledged.
文摘Refractory high entropy alloys feature outstanding properties making them a promising materials class for next-generation hightemperature applications.At high temperatures,materials properties are strongly affected by lattice vibrations(phonons).Phonons critically influence thermal stability,thermodynamic and elastic properties,as well as thermal conductivity.In contrast to perfect crystals and ordered alloys,the inherently present mass and force constant fluctuations in multi-component random alloys(high entropy alloys)can induce significant phonon scattering and broadening.Despite their importance,phonon scattering and broadening have so far only scarcely been investigated for high entropy alloys.We tackle this challenge from a theoretical perspective and employ ab initio calculations to systematically study the impact of force constant and mass fluctuations on the phonon spectral functions of 12 body-centered cubic random alloys,from binaries up to 5-component high entropy alloys,addressing the key question of how chemical complexity impacts phonons.We find that it is crucial to include both mass and force constant fluctuations.If one or the other is neglected,qualitatively wrong results can be obtained such as artificial phonon band gaps.We analyze how the results obtained for the phonons translate into thermodynamically integrated quantities,specifically the vibrational entropy.Changes in the vibrational entropy with increasing the number of elements can be as large as changes in the configurational entropy and are thus important for phase stability considerations.The set of studied alloys includes MoTa,MoTaNb,MoTaNbW,MoTaNbWV,VW,VWNb,VWTa,VWNbTa,VTaNbTi,VWNbTaTi,HfZrNb,HfMoTaTiZr.
基金supported by the following funding awards:Grants-in-Aid for Scientific Research in Innovative Area(no.22102003)Scientific Research(A)(no.23246025)+1 种基金Challenging Exploratory Research(no.25630013)the Elements Strategy Initiative for Structural Materials(ESISM).
文摘Rejuvenation is the structural excitation of glassy materials,and is a promising approach for improving the macroscopic deformability of metallic glasses.This atomistic study proposes the application of compressive hydrostatic pressure during the glass-forming quenching process and demonstrates highly rejuvenated glass states that have not been attainable without the application of pressure.Surprisingly,the pressure-promoted rejuvenation process increases the characteristic short-and mediumrange order,even though it leads to a higher-energy glassy state.This‘local order’–‘energy’relation is completely opposite to conventional thinking regarding the relation,suggesting the presence of a well-ordered high-pressure glass/high-energy glass phase.We also demonstrate that the rejuvenated glass made by the pressure-promoted rejuvenation exhibits greater plastic performance than as-quenched glass,and greater strength and stiffness than glass made without the application of pressure.It is thus possible to tune the mechanical properties of glass using the pressure-promoted rejuvenation technique.
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Funding by the Ministry of Education,Culture,Sports,Science,and Technology(MEXT)Japan,through Elements Strategy Initiative for Structural Materials(ESISM)of Kyoto University+4 种基金by the Japan Society for the Promotion of Science(JSPS)KAKENHI Grant-in-Aid for Young Scientist(B)(Grant No.16K18228)by the European Research Council under the EU’s 7th Framework Programme(FP7/2007-2013)/ERC Grant agreement 290998the Grant-in-Aid for Scientific Research on Innovative Areas Nano Informatics(Grant No.25106005)from the Japan Society for the Promotion of Science(JSPS)by the Deutsche Forschungsgemeinschaft(DFG)for the scholarship KO 5080/1-1by the DFG for their funding within the priority programme SPP 1599.
文摘A first-principles-based computational tool for simulating phonons of magnetic random solid solutions including thermal magnetic fluctuations is developed.The method takes fluctuations of force constants due to magnetic excitations as well as due to chemical disorder into account.The developed approach correctly predicts the experimentally observed unusual phonon hardening of a transverse acoustic mode in Fe–Pd an Fe–Pt Invar alloys with increasing temperature.This peculiar behavior,which cannot be explained within a conventional harmonic picture,turns out to be a consequence of thermal magnetic fluctuations.The proposed methodology can be straightforwardly applied to a wide range of materials to reveal new insights into physical behaviors and to design materials through computation,which were not accessible so far.
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 JST Industry-Academia Collaborative Programs,“Materials Strength from Hamiltonian”,and by the Elements Strategy Initiative for Structural Materials(ESISM)through MEXT,Japansupported by a Grant-in-Aid for Scientific Research on Innovative Area“Bulk Nanostructured Metals”and by the Computational Materials Science Initiative(CMSI),MEXT,Japanthe K computer provided by the RIKEN Advanced Institute for Computational Science through the HPCI System Research project(Project ID:hp130016,hp140233,hp150235).
文摘The physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method,molecular dynamics simulation,etc,applied to homogeneous and heterogeneous systems.Firstly,we examined the elastic properties based on electronic structure calculations in a homogeneous system and attributed the physical origin of the loss of ductility with increasing Si content to the combined effects of magneto-volume and D03 ordering.As a typical example of a heterogeneity forming a microstructure,we focus on grain boundaries,and segregation behavior of Si atoms is studied through high-precision electronic structure calculations.Two kinds of segregation sites are identified:looser and tighter sites.Depending on the site,different segregation mechanisms are revealed.Finally,the dislocation behavior in the Fe-Si alloy is investigated mainly by molecular dynamics simulations combined with electronic structure calculations.The solid-solution hardening and softening are interpreted in terms of two kinds of energy barriers for kink nucleation and migration on a screw dislocation line.Furthermore,the clue to the peculiar work hardening behavior is discussed based on kinetic Monte Carlo simulations by focusing on the preferential selection of slip planes triggered by kink nucleation.