The effect of high-energy electropulsing-ultrasonic surface treatment(EUST) on the surface properties and the microstructure evolution of C45 E4 steel was investigated. Refined microstructure and reduced surface rough...The effect of high-energy electropulsing-ultrasonic surface treatment(EUST) on the surface properties and the microstructure evolution of C45 E4 steel was investigated. Refined microstructure and reduced surface roughness were obtained owing to the surface nanocrystallization process. Compared with the ultrasonic surface treatment(UST), the impact depth of the surface strengthened layer was increased by 40% to 700 μm after EUST. The average grain size of the surface nanocrystallization layer was reduced to 30-50 nm. The surface roughness of the C45 E4 steel was reduced to 0.25 μm, and the surface microhardness was dramatically enhanced to 460 HV. The improvement of microstructure and micro-hardness at ambient temperature was likely attributed to the acceleration of atomic diffusion and the enhancement of plastic deformation ability in the surface strengthened layer under the influence of electropulsing. Due to the electropulsing-assisted ultrasonic strengthening effect, the surface nanocrystallization in this ultrafast procedure was noticeably enhanced.展开更多
In order to expand the application of steel 20 in precision device,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 20. The FMRR samples are then Cr-Rare ear...In order to expand the application of steel 20 in precision device,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 20. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The microstructure of the top surface layer is characterized by transmission electron microscopy( TEM). Microhardness of the top surface is measured by a Vickers microhardness tester. The boride layer is characterized by using scanning electron microscopy( SEM).Experimental results show that a nanostructured layer with their grain size range from 200 to 400 nm is obtained in the top surface layer. The microhardness of FMRR sample changes gradiently along the depth from about274 HV in the top surface layer to about 159 HV in the matrix,which is nearly 1.7 times harder than that of the original sample. The penetrating rate is enhanced significantly when the FMRR samples are Cr-Rare earthboronized at 600 ℃ for 6 h. Thickness of the boride layer increases to around 20 μm,which is nearly twice thicker than that of the original sample.展开更多
In this paper,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 45. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The boride layer ...In this paper,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 45. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The boride layer is characterized by using Scanning electron microscopy( SEM) and X-ray diffraction( XRD).Experimental results indicate that the thickness of the boride layer is greatly increased by surface nanocrystallization. The boride layer with relatively continuous structure instead of the zigzag teeth structure is obtained,and the penetrating rate is enhanced by 2. 5-3. 7 times when the FMRR samples are Cr-Rare earthboronized at the temperature of 570 ℃,600 ℃ and 650 ℃ for 6 h. The boride layer fabricated on the FMRR sample consists of single phase Fe2 B. Severe plastic deformation with the grain size of approximately 100 nm in the top surface layer of steel 45 is observed,and the thickness of the plastic deformation layer is about 30 μm.The microstructure in the top surface layer is characterized by Transmission electron microscopy( TEM). Grain boundaries are largely increased with high stacking fault energy after FMRR, leading to a significant enhancement of RE boron-chromizing speed.展开更多
Bymeans of the local surface nanocrystallization that enables to change the material on local positions,an innovative embedded multi-cell(EMC)thin-walled energy absorption structures with local surface nanocrystalliza...Bymeans of the local surface nanocrystallization that enables to change the material on local positions,an innovative embedded multi-cell(EMC)thin-walled energy absorption structures with local surface nanocrystallization is proposed in this paper.The local surface nanacrystallization stripes are regarded as the moving morphable components in the domain for optimal design.Results reveal that after optimizing the local surface nanocrystallization layout,the specific energy absorption(SEA)is increased by 50.78%compared with the untreated counterpart.Besides,in contrast with the optimized 4-cell structure,the SEA of the nanocrystallized embedded 9-cell structure is further enhanced by 27.68%,in contrast with the 9-cell structure,the SEA of the nanocrystallized embedded clapboard type 9-cell structure is enhanced by 3.61%.Thismethod provides a guidance for the design of newenergy absorption devices.展开更多
As a means of surface modification process,metal surface nanocrystallization(MSN) has attracted widespread attention and enjoyed a great prospect.However,currently little research is carried out regarding MSN of welde...As a means of surface modification process,metal surface nanocrystallization(MSN) has attracted widespread attention and enjoyed a great prospect.However,currently little research is carried out regarding MSN of welded joint.The processes of high energy shot peening(HESP) technology and ultrasonic impact treatment(UIT) were carried out to achieve joint surface nanocrystallization.The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer,the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy,the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine.The results show that both of the processes can achieve welded joint surface nanocrystallization and the weld after HESP have smaller grain size,larger deformation layer thickness and higher hardness values than those after UIT.However,HESP is restrained by the shapes and sizes of welding materials,so the UIT process is preferred to use in the general engineering practical applications.展开更多
Surface nanocrystallization(SNC) has proved to be an effective approach to improve the overall properties of bulk metallic materials.Recently,a new surface nanocrystallization technique,i.e.,surface mechanical grindin...Surface nanocrystallization(SNC) has proved to be an effective approach to improve the overall properties of bulk metallic materials.Recently,a new surface nanocrystallization technique,i.e.,surface mechanical grinding treatment(SMGT),was developed.In this work,a gradient nano-micro structure was achieved in the surface layer of the AISI 52100 steel by using SMGT.We obtained a minimum grain size of about 7nm in the top surface layer.The total thickness of the deformed layer is over 200 micrometer.Meanwhile the surface roughness is rather low. Ferrite grains were deformed to different extents varying with depth from the top surface.Gradient grain sizes were formed from top surface to deep matrix which offered a great opportunity to study the refinement process of the ferrite grains.It is found that dislocation activities play a dominant role in the process.At the initiate stage, dislocations accumulated and interacted to form dense dislocation walls and cells.Increasing strain and strain rate induced more dislocation walls in cells,forming finer cells.This procedure continued until nanograins formed at the top most surface. The existence of cementite particles in ferrite matrix greatly facilitates the ferrite refinement process.Boundaries between ferrites and cementites offered many dislocation sources which accelerate the propagation of dislocations. Dislocation walls were blocked by cementites which certainly lead to finer dislocation cells.The existence of cementites makes it easier to generate fresh dislocation walls in sub-micron grains.A strain gradient was formed from a cementite particle to surrounding ferrite grains.This strain gradient gives rise to more geometric necessary dislocations. As ferrite grain size decreased less than that of cementite particles,fragmentation occurred in cementites.Hard second phase was usually considered as brittle.In this work,evidences of deformation(traces of dislocation activities) in cementites were distinct.Since the stress concentration in the phase boundary(especially triple junction) excesses the shear modulus of cementite,dislocation emission was triggered.It is found in this work that dislocations tend to slip along parallel planes,possibly on(001),(01 0),(100),(110),(10 1 ) and(011) planes,depending upon as the load directions.展开更多
In this paper,a local surface nanocrystallization technology is used for thin-walled structures with square cross sections,and an energy absorption device of two-staged combined energy absorption structure is proposed...In this paper,a local surface nanocrystallization technology is used for thin-walled structures with square cross sections,and an energy absorption device of two-staged combined energy absorption structure is proposed.In virtue of the surface nanocrystallization that enables to change the material on local positions,the structural deformation is induced and controlled to maximize the energy absorption capacity.A numerical model of the two-staged combined energy absorption structure is established,and the local surface nanocrystallization layout is optimized.The results show that the specific energy absorption of two-staged combined structure with local surface nanocrystallization can be increased by 34.36%compared with the untreated counterpart of the same material and structural shape.The ratio between the first and second peak crushing forces and the energy absorption allocation ratio between the two stages can be adjusted in the ranges of 0.26–0.55 and 0.31–0.45,respectively,which can be controlled by the local surface nanocrystallization designs.The numerical simulation and experimental results are in good agreement,which shows that the design for energy absorption device with local surface nanocrystallization is feasible and effective.展开更多
Mg alloy casting parts commonly suffer from drawbacks of low surface properties,high susceptibility to corrosion,unsatisfactory absolute strength,and poor ductility,which seriously limit their wide application.Here,a ...Mg alloy casting parts commonly suffer from drawbacks of low surface properties,high susceptibility to corrosion,unsatisfactory absolute strength,and poor ductility,which seriously limit their wide application.Here,a surface nanocrystallization technique,i.e.,ultrasonic surface rolling(USR),was applied on an as-cast AZ91 Mg alloy sheet to improve its corrosion resistance and mechanical properties.The USR produces double smooth surfaces with Ra 0.036μm and gradient nanostructured surface layers on the sheet.Due to this special microstructure modification,the USR sheet exhibits 55%and 50%improvements in yield strength and ultimate tensile strength without visibly sacrificed ductility comparable to its untreated counterpart,as well as a 24%improvement in surface hardness.The USR sheet also shows good corrosion resistance in 3.5wt%NaCl aqueous solution.The corrosion current density of the USR sheet reduces by 63%after immersion for 1 h,and 25%after immersion for 24 h compared to that of the untreated counterpart.The enhanced strength and hardness are mainly related to the gradient nanostructure.The improved corrosion resistance is mainly ascribed to the decreased surface roughness,nanostructured surface,and residual compressive stress.The present results state that USR is an effective and attractive method to improve the multiple properties of Mg alloy cast-ing parts,and thus can be used as an additional and last working procedure to achieve high-performance Mg alloy casting parts.展开更多
In the present work,surface mechanical attrition treatment(SMAT)was proposed to achieve surface nanocrystallization on Ti-6Al-4V surface via high-energy planetary ball milling method using a planetary ball mill.The ch...In the present work,surface mechanical attrition treatment(SMAT)was proposed to achieve surface nanocrystallization on Ti-6Al-4V surface via high-energy planetary ball milling method using a planetary ball mill.The characteristics of microstructure were studied using different methods.Surface nanocrystallization is achieved on Ti-6Al-4V substrate.The process of refinement could be summarized into four steps.During the refinement process,the reticular continuous beta phase performs a significant role,it cracked,broke up and moved to each side along the grain boundaries.The movement of beta grains has the capabilities of effectively optimizing the grain orientation and accelerating the further refinement of alpha grains.Twinning also plays an important role during the refinement.The grain orientation between different types of grains seems to be larger than that of same type grains.The interface will be divided into smaller nanocrystalline grains once the dislocation density breaks the threshold.Then,the balance will be achieved again and owns a higher critical value which cannot be broken,then a stable grain size can be achieved ultimately.The results of microhardness,friction coefficient and wear mass loss tests of SMAT samples indicate that the mechanical behaviors of substrate are greatly enhanced after this novel SMAT treatment.展开更多
In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification(UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and ...In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification(UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The nearsurface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.展开更多
Ultrasonic nanocrystal surface modification (UNSM) treatment on non-equiatomic medium-and highentropy alloy (HEA) of Fex(CoCrMnNi)100-xis firstly introduced and its impact on microstructure and mechanical properties a...Ultrasonic nanocrystal surface modification (UNSM) treatment on non-equiatomic medium-and highentropy alloy (HEA) of Fex(CoCrMnNi)100-xis firstly introduced and its impact on microstructure and mechanical properties are revealed.By UNSM,severe plastic deformation-induced dislocation and deformation twins (DTs) arise at the topmost surface.Especially,Fe60(CoCrMnNi)40(Fe60),which is classified as a medium-entropy alloy (MEA),exhibits ε-martensitic transformation.In the room temperature tensile test,a high strength of ~600 MPa and ductility of ~65%elongation (strain to failure) is accomplished in Fe60.Initially formed DTs and ε-martensitic transformation by UNSM treatment plays a key role in retardation of necking point via both twinning-induced plasticity and transformation-induced plasticity.However,Fe20(CoCrMnNi)80(Fe20) comparatively shows low strength of ~550 MPa and ~40% elongation,owing to the low accommodation of DTs than Fe60.Our research will provide new guidelines for enhancing the mechanical properties of MEA and HEA.展开更多
基金Funded by the Natural Science Foundation of China(No.50571048)the Research & Development Funding Project of Shenzhen(No.JCYJ20120619152539900)
文摘The effect of high-energy electropulsing-ultrasonic surface treatment(EUST) on the surface properties and the microstructure evolution of C45 E4 steel was investigated. Refined microstructure and reduced surface roughness were obtained owing to the surface nanocrystallization process. Compared with the ultrasonic surface treatment(UST), the impact depth of the surface strengthened layer was increased by 40% to 700 μm after EUST. The average grain size of the surface nanocrystallization layer was reduced to 30-50 nm. The surface roughness of the C45 E4 steel was reduced to 0.25 μm, and the surface microhardness was dramatically enhanced to 460 HV. The improvement of microstructure and micro-hardness at ambient temperature was likely attributed to the acceleration of atomic diffusion and the enhancement of plastic deformation ability in the surface strengthened layer under the influence of electropulsing. Due to the electropulsing-assisted ultrasonic strengthening effect, the surface nanocrystallization in this ultrafast procedure was noticeably enhanced.
文摘In order to expand the application of steel 20 in precision device,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 20. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The microstructure of the top surface layer is characterized by transmission electron microscopy( TEM). Microhardness of the top surface is measured by a Vickers microhardness tester. The boride layer is characterized by using scanning electron microscopy( SEM).Experimental results show that a nanostructured layer with their grain size range from 200 to 400 nm is obtained in the top surface layer. The microhardness of FMRR sample changes gradiently along the depth from about274 HV in the top surface layer to about 159 HV in the matrix,which is nearly 1.7 times harder than that of the original sample. The penetrating rate is enhanced significantly when the FMRR samples are Cr-Rare earthboronized at 600 ℃ for 6 h. Thickness of the boride layer increases to around 20 μm,which is nearly twice thicker than that of the original sample.
文摘In this paper,fast multiple rotation rolling( FMRR) is applied to fabricate a nanostructured layer on the surface of steel 45. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The boride layer is characterized by using Scanning electron microscopy( SEM) and X-ray diffraction( XRD).Experimental results indicate that the thickness of the boride layer is greatly increased by surface nanocrystallization. The boride layer with relatively continuous structure instead of the zigzag teeth structure is obtained,and the penetrating rate is enhanced by 2. 5-3. 7 times when the FMRR samples are Cr-Rare earthboronized at the temperature of 570 ℃,600 ℃ and 650 ℃ for 6 h. The boride layer fabricated on the FMRR sample consists of single phase Fe2 B. Severe plastic deformation with the grain size of approximately 100 nm in the top surface layer of steel 45 is observed,and the thickness of the plastic deformation layer is about 30 μm.The microstructure in the top surface layer is characterized by Transmission electron microscopy( TEM). Grain boundaries are largely increased with high stacking fault energy after FMRR, leading to a significant enhancement of RE boron-chromizing speed.
基金Dalian Innovation Foundation of Science and Technology(2018J11CY005)State Key Laboratory of Structural Analysis for Industrial Equipment(S18313)are gratefully acknowledged.
文摘Bymeans of the local surface nanocrystallization that enables to change the material on local positions,an innovative embedded multi-cell(EMC)thin-walled energy absorption structures with local surface nanocrystallization is proposed in this paper.The local surface nanacrystallization stripes are regarded as the moving morphable components in the domain for optimal design.Results reveal that after optimizing the local surface nanocrystallization layout,the specific energy absorption(SEA)is increased by 50.78%compared with the untreated counterpart.Besides,in contrast with the optimized 4-cell structure,the SEA of the nanocrystallized embedded 9-cell structure is further enhanced by 27.68%,in contrast with the 9-cell structure,the SEA of the nanocrystallized embedded clapboard type 9-cell structure is enhanced by 3.61%.Thismethod provides a guidance for the design of newenergy absorption devices.
基金supported by the National Natural Science Foundation(No.50765003)and the National Natural Science Foundation(No.51165026)
文摘As a means of surface modification process,metal surface nanocrystallization(MSN) has attracted widespread attention and enjoyed a great prospect.However,currently little research is carried out regarding MSN of welded joint.The processes of high energy shot peening(HESP) technology and ultrasonic impact treatment(UIT) were carried out to achieve joint surface nanocrystallization.The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer,the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy,the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine.The results show that both of the processes can achieve welded joint surface nanocrystallization and the weld after HESP have smaller grain size,larger deformation layer thickness and higher hardness values than those after UIT.However,HESP is restrained by the shapes and sizes of welding materials,so the UIT process is preferred to use in the general engineering practical applications.
文摘Surface nanocrystallization(SNC) has proved to be an effective approach to improve the overall properties of bulk metallic materials.Recently,a new surface nanocrystallization technique,i.e.,surface mechanical grinding treatment(SMGT),was developed.In this work,a gradient nano-micro structure was achieved in the surface layer of the AISI 52100 steel by using SMGT.We obtained a minimum grain size of about 7nm in the top surface layer.The total thickness of the deformed layer is over 200 micrometer.Meanwhile the surface roughness is rather low. Ferrite grains were deformed to different extents varying with depth from the top surface.Gradient grain sizes were formed from top surface to deep matrix which offered a great opportunity to study the refinement process of the ferrite grains.It is found that dislocation activities play a dominant role in the process.At the initiate stage, dislocations accumulated and interacted to form dense dislocation walls and cells.Increasing strain and strain rate induced more dislocation walls in cells,forming finer cells.This procedure continued until nanograins formed at the top most surface. The existence of cementite particles in ferrite matrix greatly facilitates the ferrite refinement process.Boundaries between ferrites and cementites offered many dislocation sources which accelerate the propagation of dislocations. Dislocation walls were blocked by cementites which certainly lead to finer dislocation cells.The existence of cementites makes it easier to generate fresh dislocation walls in sub-micron grains.A strain gradient was formed from a cementite particle to surrounding ferrite grains.This strain gradient gives rise to more geometric necessary dislocations. As ferrite grain size decreased less than that of cementite particles,fragmentation occurred in cementites.Hard second phase was usually considered as brittle.In this work,evidences of deformation(traces of dislocation activities) in cementites were distinct.Since the stress concentration in the phase boundary(especially triple junction) excesses the shear modulus of cementite,dislocation emission was triggered.It is found in this work that dislocations tend to slip along parallel planes,possibly on(001),(01 0),(100),(110),(10 1 ) and(011) planes,depending upon as the load directions.
基金In this research work,the Aeronautical Science Foundation of China(2018ZC63003)State Key Laboratory of Structural Analysis for Industrial Equipment(G19109,S18313)are gratefully acknowledged.
文摘In this paper,a local surface nanocrystallization technology is used for thin-walled structures with square cross sections,and an energy absorption device of two-staged combined energy absorption structure is proposed.In virtue of the surface nanocrystallization that enables to change the material on local positions,the structural deformation is induced and controlled to maximize the energy absorption capacity.A numerical model of the two-staged combined energy absorption structure is established,and the local surface nanocrystallization layout is optimized.The results show that the specific energy absorption of two-staged combined structure with local surface nanocrystallization can be increased by 34.36%compared with the untreated counterpart of the same material and structural shape.The ratio between the first and second peak crushing forces and the energy absorption allocation ratio between the two stages can be adjusted in the ranges of 0.26–0.55 and 0.31–0.45,respectively,which can be controlled by the local surface nanocrystallization designs.The numerical simulation and experimental results are in good agreement,which shows that the design for energy absorption device with local surface nanocrystallization is feasible and effective.
基金This work was financially supported by the National Natural Science Foundation of China(No.U1910212)the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Mg alloy casting parts commonly suffer from drawbacks of low surface properties,high susceptibility to corrosion,unsatisfactory absolute strength,and poor ductility,which seriously limit their wide application.Here,a surface nanocrystallization technique,i.e.,ultrasonic surface rolling(USR),was applied on an as-cast AZ91 Mg alloy sheet to improve its corrosion resistance and mechanical properties.The USR produces double smooth surfaces with Ra 0.036μm and gradient nanostructured surface layers on the sheet.Due to this special microstructure modification,the USR sheet exhibits 55%and 50%improvements in yield strength and ultimate tensile strength without visibly sacrificed ductility comparable to its untreated counterpart,as well as a 24%improvement in surface hardness.The USR sheet also shows good corrosion resistance in 3.5wt%NaCl aqueous solution.The corrosion current density of the USR sheet reduces by 63%after immersion for 1 h,and 25%after immersion for 24 h compared to that of the untreated counterpart.The enhanced strength and hardness are mainly related to the gradient nanostructure.The improved corrosion resistance is mainly ascribed to the decreased surface roughness,nanostructured surface,and residual compressive stress.The present results state that USR is an effective and attractive method to improve the multiple properties of Mg alloy cast-ing parts,and thus can be used as an additional and last working procedure to achieve high-performance Mg alloy casting parts.
基金financially supported by the National Natural Science Foundation of China(No.51475232)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD,Basic Research on Metal Surface Modification by Surface Mechanical Attrition Treatment)the Foundation of Graduate Innovation Center in NUAA and the Fundamental Research Funds for the Central Universities(No.Kfjj20150605)。
文摘In the present work,surface mechanical attrition treatment(SMAT)was proposed to achieve surface nanocrystallization on Ti-6Al-4V surface via high-energy planetary ball milling method using a planetary ball mill.The characteristics of microstructure were studied using different methods.Surface nanocrystallization is achieved on Ti-6Al-4V substrate.The process of refinement could be summarized into four steps.During the refinement process,the reticular continuous beta phase performs a significant role,it cracked,broke up and moved to each side along the grain boundaries.The movement of beta grains has the capabilities of effectively optimizing the grain orientation and accelerating the further refinement of alpha grains.Twinning also plays an important role during the refinement.The grain orientation between different types of grains seems to be larger than that of same type grains.The interface will be divided into smaller nanocrystalline grains once the dislocation density breaks the threshold.Then,the balance will be achieved again and owns a higher critical value which cannot be broken,then a stable grain size can be achieved ultimately.The results of microhardness,friction coefficient and wear mass loss tests of SMAT samples indicate that the mechanical behaviors of substrate are greatly enhanced after this novel SMAT treatment.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant number NRF2019R1A2C1088535)supported by Nano Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICTFuture Planning (Grant number 2009-0082580)。
文摘In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification(UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The nearsurface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.
基金financially supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.NRF-2019R1A2C1088535)supported by the Nano Material Technology Development Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT and Future Planning(No.2009-0082580)。
文摘Ultrasonic nanocrystal surface modification (UNSM) treatment on non-equiatomic medium-and highentropy alloy (HEA) of Fex(CoCrMnNi)100-xis firstly introduced and its impact on microstructure and mechanical properties are revealed.By UNSM,severe plastic deformation-induced dislocation and deformation twins (DTs) arise at the topmost surface.Especially,Fe60(CoCrMnNi)40(Fe60),which is classified as a medium-entropy alloy (MEA),exhibits ε-martensitic transformation.In the room temperature tensile test,a high strength of ~600 MPa and ductility of ~65%elongation (strain to failure) is accomplished in Fe60.Initially formed DTs and ε-martensitic transformation by UNSM treatment plays a key role in retardation of necking point via both twinning-induced plasticity and transformation-induced plasticity.However,Fe20(CoCrMnNi)80(Fe20) comparatively shows low strength of ~550 MPa and ~40% elongation,owing to the low accommodation of DTs than Fe60.Our research will provide new guidelines for enhancing the mechanical properties of MEA and HEA.
