Recently,a Schwarz crystal structure with curved grain boundaries(GBs)constrained by twin-boundary(TB)networks was discovered in nanocrystalline Cu through experiments and atomistic simulations.Nanocrystalline Cu with...Recently,a Schwarz crystal structure with curved grain boundaries(GBs)constrained by twin-boundary(TB)networks was discovered in nanocrystalline Cu through experiments and atomistic simulations.Nanocrystalline Cu with nanosized Schwarz crystals exhibited high strength and excellent thermal stability.However,the grainsize effect and associated deformation mechanisms of Schwarz nanocrystals remain unknown.Here,we performed large-scale atomistic simulations to investigate the deformation behaviors and grain-size effect of nanocrystalline Cu with Schwarz crystals.Our simulations showed that similar to regular nanocrystals,Schwarz nanocrystals exhibit a strengthening-softening transition with decreasing grain size.The critical grain size in Schwarz nanocrystals is smaller than that in regular nanocrystals,leading to a maximum strength higher than that of regular nanocrystals.Our simulations revealed that the softening in Schwarz nanocrystals mainly originates from TB migration(or detwinning)and annihilation of GBs,rather than GB-mediated processes(including GB migration,sliding and diffusion)dominating the softening in regular nanocrystals.Quantitative analyses of simulation data further showed that compared with those in regular nanocrystals,the GB-mediated processes in Schwarz nanocrystals are suppressed,which is related to the low volume fraction of amorphous-like GBs and constraints of TB networks.The smaller critical grain size arises from the suppression of GB-mediated processes.展开更多
The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peenin...The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peening(HESP) commonly used to prepare nanostructured surface layers can be achieved by the increase of pill size, pill speed, and treatment time in the commercial shot peening equipment. XRD, SEM and TEM were used to characterize the surface layer microstructure of treated specimens. The analytic results show that the main deformation mode of commercial pure Ti is twinning. At the beginning of deformation, the dislocations are formed and twins occur within or on plane, then twins in intersection plane appear, and at last the twin characteristics disappear in the surface layer after longer treatment time. The deformation layer depth increases with treatment time in a certain period when the pill size and speed are unchanged. And in the severe plastic deformation (SPD) layer in which the twins are not identified easily by using SEM, the nanocrystalline microstructures are found under TEM. The finest grain size in the surface layer is about 40 nm, and the depth of nanostructured layers is over 60 μm. The microhardness of the nanostructured surface layers is enhanced significantly after shot peening compared with that of the initial simple.展开更多
Dissolution of cementite was found in the surface layer of 1.0C-1.5Cr steel plates during the process of surface mechanical attrition treatment(SMAT),and its evolution was characterized by transmission electron micros...Dissolution of cementite was found in the surface layer of 1.0C-1.5Cr steel plates during the process of surface mechanical attrition treatment(SMAT),and its evolution was characterized by transmission electron microscope(TEM),three-dimensional atom probe(3DAP)and Mssbauer spectroscopy.The average grain size contained in the top surface of SMAT specimen was 10nm,and no diffraction ring corresponding to cementite grain was identified in the selected area election diffraction(SAED)pattern,which indicated the disappearance of cementite.3DAP analysis showed the average carbon concentration in ferrite(0.75 at%)after SMAT,which was almost 100 times higher than that in matrix(0.008 at%),which suggested cementite dissolve in the process of SMAT.The results of Mssbauer spectroscopy indicated that partial cementite dissolved in the process of SMAT,the saturation of cementite dissolution is about 47%.Evolution of cementite involved three sub-stages:①inoculation stage,in the first 5 min of treated duration,cementite fraction is reduced only by 0.4%;②dissolution stage,within the following 25 min cementite fraction significantly is reduced from 14.6% to 8.4%;③saturation stage,when treatment exceeds 30 min,the fraction of cementite nearly remains the same.展开更多
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 rou...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
A nanocrystallization surface layer was successfully obtained in a sample of Ti6Al4V. The microstructure features of the sample were characterized by using X-ray diffraction analysis(XRD), scanning electron microscopy...A nanocrystallization surface layer was successfully obtained in a sample of Ti6Al4V. The microstructure features of the sample were characterized by using X-ray diffraction analysis(XRD), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) observations. The average grain size in the top surface layer is about 10nm, and gradually increases with the distance from the surface increasing.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
The nanocrystallization behaviour of Zr70Cu20Ni10 metallic glass during isothermal annealing is studied by employing a Monte Carlo simulation incorporating with a modified Ising model and a Q-state Potts model. Based ...The nanocrystallization behaviour of Zr70Cu20Ni10 metallic glass during isothermal annealing is studied by employing a Monte Carlo simulation incorporating with a modified Ising model and a Q-state Potts model. Based on the simulated microstructure and differential scanning calorimetry curves, we find that the low crystal-amorphous interface energy of Ni plays an important role in the nanocrystallization of primary Zr2Ni. It is found that when T〈T1max (where T1max is the temperature with maximum nucleation rate), the increase of temperature results in a larger growth rate and a much finer mierostrueture for the primary Zr2Ni, which accords with the microstructure evolution in "flash annealing". Finally, the Zr2Ni/Zr2Cu interface energy σG contributes to the pinning effect of the primary nano-sized Zr2Ni grains in the later formed normal Zr2Cu grains.展开更多
The hydriding of as-cast Mg-5.5%Zn-0.6%Zr(ZK60 Mg)(mass fraction)alloy was achieved by room-temperature reaction milling in hydrogen,with the mechanical energy serving as the driving force for the process.The hydridin...The hydriding of as-cast Mg-5.5%Zn-0.6%Zr(ZK60 Mg)(mass fraction)alloy was achieved by room-temperature reaction milling in hydrogen,with the mechanical energy serving as the driving force for the process.The hydriding progress during milling was examined by hydrogen absorption measurement,and the microstructure change was characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM),respectively.The results show that,by room-temperature reaction milling in hydrogen,the as-cast ZK60 Mg alloy can be fully hydrided to form a nanocrystalline MgH_(2) single-phase microstructure.In particular,the average grain size of the MgH_(2) phase obtained by room-temperature reaction milling in hydrogen for 16.2 h is about 8-10 nm,and the average particle size of the as-milled hydrided powders is 2-3μm.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
Size distribution of nano-carbides produced by duplex treatments of surface nanocrystallization(by surface severe plastic deformation) and plasma electrolytic carburizing on CP-Ti was investigated.Skewness and kurtosi...Size distribution of nano-carbides produced by duplex treatments of surface nanocrystallization(by surface severe plastic deformation) and plasma electrolytic carburizing on CP-Ti was investigated.Skewness and kurtosis of Gussian shape distribution curves were studied and the effect of time was determined.The usage of longer time is more suitable for achieving less size of complex nano-carbides.Surface roughness of treated samples was measured.It is observed that there is an optimum level for time on surface roughness increasing(difference between two measured data).展开更多
High-energy shot peening (HESP), a method to produce severe plastic deformation by high velocity flying balls, was applied on die cast magnesium alloy AZ91D. Effects of surface nanocrystallization by HESP and heat t...High-energy shot peening (HESP), a method to produce severe plastic deformation by high velocity flying balls, was applied on die cast magnesium alloy AZ91D. Effects of surface nanocrystallization by HESP and heat treatment at different temperatures were investigated. The mi- crostructure evolution was conducted using X-ray diffraction (XRD) and field emission scanning electronic microscopy (FESEM). The hardness was measured by microhardness tester. The experimental results show that surface nanocrystrallization of AZ91D obtained by HESP would lead to the increase of microhardness. Low temperature heated at 100℃ for 1 h do not change the property obviously. However, both the microstructure and microhardness vary greatly after heat treatment at 400℃ for 1 h.展开更多
In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray di...In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray diffraction (XRD) and transmission electron microscope (TEM), and the results showed that the mean grain size of the surface was refined to nm Ievel after SMAT treatment. Nanocrystallized surface layers were formed after treated for 5, 15, 30 and 60 min. Microhardness experimental results implied the microhardness obviously increased on the surface layer and it also showed the variation of microhardness at the cross section. Corrosion test results showed the corrosion resistance of the surfaces in the original commercial pure titanium treated by SMAT was not improved in HCI solution. The corrosion micrographs were observed by scanning electron microscope (SEM).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
The microstructures of the nanocrystalline surface layer of a quenched and high temperature tempered 0. 4C- 1Cr steel induced by high-power surface processing (HPSP) technique were characterized by scan- ning eleetr...The microstructures of the nanocrystalline surface layer of a quenched and high temperature tempered 0. 4C- 1Cr steel induced by high-power surface processing (HPSP) technique were characterized by scan- ning eleetron microscopy and transmission electron microscopy. The results indicate that a nanocrystalline layer was fabricated on the surface of the steel 19 using HPSP treatment. The mean grain size in the surface layer is about 11 nm. The nanocrystallization of cementite is prior to that of the matrix phase, ferrite.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...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 nanocrystaUization 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
基金the financial support from National Natural Science Foundation of China (Grants Nos.12325203,91963117,and 11921002)。
文摘Recently,a Schwarz crystal structure with curved grain boundaries(GBs)constrained by twin-boundary(TB)networks was discovered in nanocrystalline Cu through experiments and atomistic simulations.Nanocrystalline Cu with nanosized Schwarz crystals exhibited high strength and excellent thermal stability.However,the grainsize effect and associated deformation mechanisms of Schwarz nanocrystals remain unknown.Here,we performed large-scale atomistic simulations to investigate the deformation behaviors and grain-size effect of nanocrystalline Cu with Schwarz crystals.Our simulations showed that similar to regular nanocrystals,Schwarz nanocrystals exhibit a strengthening-softening transition with decreasing grain size.The critical grain size in Schwarz nanocrystals is smaller than that in regular nanocrystals,leading to a maximum strength higher than that of regular nanocrystals.Our simulations revealed that the softening in Schwarz nanocrystals mainly originates from TB migration(or detwinning)and annihilation of GBs,rather than GB-mediated processes(including GB migration,sliding and diffusion)dominating the softening in regular nanocrystals.Quantitative analyses of simulation data further showed that compared with those in regular nanocrystals,the GB-mediated processes in Schwarz nanocrystals are suppressed,which is related to the low volume fraction of amorphous-like GBs and constraints of TB networks.The smaller critical grain size arises from the suppression of GB-mediated processes.
基金Project(50171017) support by the National Natural Science Foundation of China project(2001101054) supported by the Science and Technology Foundation of Liaoning Province project(02H25008) supported by the Aeronautical Basic Science Foundation
文摘The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peening(HESP) commonly used to prepare nanostructured surface layers can be achieved by the increase of pill size, pill speed, and treatment time in the commercial shot peening equipment. XRD, SEM and TEM were used to characterize the surface layer microstructure of treated specimens. The analytic results show that the main deformation mode of commercial pure Ti is twinning. At the beginning of deformation, the dislocations are formed and twins occur within or on plane, then twins in intersection plane appear, and at last the twin characteristics disappear in the surface layer after longer treatment time. The deformation layer depth increases with treatment time in a certain period when the pill size and speed are unchanged. And in the severe plastic deformation (SPD) layer in which the twins are not identified easily by using SEM, the nanocrystalline microstructures are found under TEM. The finest grain size in the surface layer is about 40 nm, and the depth of nanostructured layers is over 60 μm. The microhardness of the nanostructured surface layers is enhanced significantly after shot peening compared with that of the initial simple.
基金supported by the National High-Tech.R&D Program of China(the National 863 plans projects,Grant No.2007AA03Z352)
文摘Dissolution of cementite was found in the surface layer of 1.0C-1.5Cr steel plates during the process of surface mechanical attrition treatment(SMAT),and its evolution was characterized by transmission electron microscope(TEM),three-dimensional atom probe(3DAP)and Mssbauer spectroscopy.The average grain size contained in the top surface of SMAT specimen was 10nm,and no diffraction ring corresponding to cementite grain was identified in the selected area election diffraction(SAED)pattern,which indicated the disappearance of cementite.3DAP analysis showed the average carbon concentration in ferrite(0.75 at%)after SMAT,which was almost 100 times higher than that in matrix(0.008 at%),which suggested cementite dissolve in the process of SMAT.The results of Mssbauer spectroscopy indicated that partial cementite dissolved in the process of SMAT,the saturation of cementite dissolution is about 47%.Evolution of cementite involved three sub-stages:①inoculation stage,in the first 5 min of treated duration,cementite fraction is reduced only by 0.4%;②dissolution stage,within the following 25 min cementite fraction significantly is reduced from 14.6% to 8.4%;③saturation stage,when treatment exceeds 30 min,the fraction of cementite nearly remains the same.
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A nanocrystallization surface layer was successfully obtained in a sample of Ti6Al4V. The microstructure features of the sample were characterized by using X-ray diffraction analysis(XRD), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) observations. The average grain size in the top surface layer is about 10nm, and gradually increases with the distance from the surface increasing.
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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 50301008 and 50231040) and the Shandong Young Scientists Foundation.
文摘The nanocrystallization behaviour of Zr70Cu20Ni10 metallic glass during isothermal annealing is studied by employing a Monte Carlo simulation incorporating with a modified Ising model and a Q-state Potts model. Based on the simulated microstructure and differential scanning calorimetry curves, we find that the low crystal-amorphous interface energy of Ni plays an important role in the nanocrystallization of primary Zr2Ni. It is found that when T〈T1max (where T1max is the temperature with maximum nucleation rate), the increase of temperature results in a larger growth rate and a much finer mierostrueture for the primary Zr2Ni, which accords with the microstructure evolution in "flash annealing". Finally, the Zr2Ni/Zr2Cu interface energy σG contributes to the pinning effect of the primary nano-sized Zr2Ni grains in the later formed normal Zr2Cu grains.
基金Project(50574034)supported by the National Natural Science Foundation of ChinaProject(20060213016)supported by Doctoral Education Fund of Ministry of Education of China。
文摘The hydriding of as-cast Mg-5.5%Zn-0.6%Zr(ZK60 Mg)(mass fraction)alloy was achieved by room-temperature reaction milling in hydrogen,with the mechanical energy serving as the driving force for the process.The hydriding progress during milling was examined by hydrogen absorption measurement,and the microstructure change was characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM),respectively.The results show that,by room-temperature reaction milling in hydrogen,the as-cast ZK60 Mg alloy can be fully hydrided to form a nanocrystalline MgH_(2) single-phase microstructure.In particular,the average grain size of the MgH_(2) phase obtained by room-temperature reaction milling in hydrogen for 16.2 h is about 8-10 nm,and the average particle size of the as-milled hydrided powders is 2-3μm.
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Partial work of this project funded by National Elite Foundation of Iran and Iranian Nanotechnology Initiative is appreciated.
文摘Size distribution of nano-carbides produced by duplex treatments of surface nanocrystallization(by surface severe plastic deformation) and plasma electrolytic carburizing on CP-Ti was investigated.Skewness and kurtosis of Gussian shape distribution curves were studied and the effect of time was determined.The usage of longer time is more suitable for achieving less size of complex nano-carbides.Surface roughness of treated samples was measured.It is observed that there is an optimum level for time on surface roughness increasing(difference between two measured data).
基金Funded by the National Ministry of Education (No.207095)Beijing Key Laboratory for Corrosion Erosion and Surface Technology
文摘High-energy shot peening (HESP), a method to produce severe plastic deformation by high velocity flying balls, was applied on die cast magnesium alloy AZ91D. Effects of surface nanocrystallization by HESP and heat treatment at different temperatures were investigated. The mi- crostructure evolution was conducted using X-ray diffraction (XRD) and field emission scanning electronic microscopy (FESEM). The hardness was measured by microhardness tester. The experimental results show that surface nanocrystrallization of AZ91D obtained by HESP would lead to the increase of microhardness. Low temperature heated at 100℃ for 1 h do not change the property obviously. However, both the microstructure and microhardness vary greatly after heat treatment at 400℃ for 1 h.
文摘In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray diffraction (XRD) and transmission electron microscope (TEM), and the results showed that the mean grain size of the surface was refined to nm Ievel after SMAT treatment. Nanocrystallized surface layers were formed after treated for 5, 15, 30 and 60 min. Microhardness experimental results implied the microhardness obviously increased on the surface layer and it also showed the variation of microhardness at the cross section. Corrosion test results showed the corrosion resistance of the surfaces in the original commercial pure titanium treated by SMAT was not improved in HCI solution. The corrosion micrographs were observed by scanning electron microscope (SEM).
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.
文摘The microstructures of the nanocrystalline surface layer of a quenched and high temperature tempered 0. 4C- 1Cr steel induced by high-power surface processing (HPSP) technique were characterized by scan- ning eleetron microscopy and transmission electron microscopy. The results indicate that a nanocrystalline layer was fabricated on the surface of the steel 19 using HPSP treatment. The mean grain size in the surface layer is about 11 nm. The nanocrystallization of cementite is prior to that of the matrix phase, ferrite.
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 nanocrystaUization 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.