Achieving high yield strength and ductility in alloys remains a significant challenge in structural materials.In this study,combined nanoprecipitation and gradient grain structure were introduced into a Co-Cr-Ni-based...Achieving high yield strength and ductility in alloys remains a significant challenge in structural materials.In this study,combined nanoprecipitation and gradient grain structure were introduced into a Co-Cr-Ni-based multi-principal element alloy(MPEA)using surface mechanical attrition treatment(SMAT).The multi-scale composite structure,featuring grain sizes refined from∼43.6μm to∼24.3 nm at the topmost surface and high-density L1_(2)nanoprecipitates within the grains,results in a substantial tensile strength of 1733 MPa and a well-maintained ductility of∼23%.The alloy with low local stacking fault energy provides sufficient flow stress to reach the critical value for twinning,a phenomenon rarely observed in MPEAs with high-density L1_(2)nanoprecipitates under quasi-static tensile conditions.The formation of nanotwins further facilitates additional strain hardening,enhancing mechanical performance at ultrahigh strength levels.This work offers significant insights into the deformation behavior of gradient-structured materials with high-density nanoprecipitates.展开更多
Titanium with gradient nano-to-micron scale grains from surface to matrix was fabricated by surface mechanical grinding treatment(SMGT) at room temperature.The SMGT-treated titanium shows higher strength than that of ...Titanium with gradient nano-to-micron scale grains from surface to matrix was fabricated by surface mechanical grinding treatment(SMGT) at room temperature.The SMGT-treated titanium shows higher strength than that of as-received one,but moderate ductility between those of ultra-fine grained(UFG) and coarse-grained titanium.Tensile stress-strain curves of SMGT-treated titanium show double strain hardening regimes.The strain hardening rate(dσ/dε) decreases with increasing strain in tensile deformation.The high strain hardening rate at initial yielding is attributed to nano-to-micron-grained surface layer.The low strain hardening rate at large plastic strain regime primarily results from coarse-grained matrix.The SMGT-treated titanium shows a ductile fracture mode with a large number of dimples.The small size of dimples in the treated surface layer is due to the combination of the high strength and strain hardening exponent.The difference between dimple size in nano-to-micron-grained surface layer and coarse-grained matrix is discussed in terms of plastic zone size at the tip of crack in the SMGT-treated titanium.展开更多
A gradient nano-grained （GNG） surface layer was fabricated on an AIS1316L stainless steel （SS） by using the surface mechanical rolling treatment （SMRT）. Reciprocating dry and oil-lubricated sliding tests of the ...A gradient nano-grained （GNG） surface layer was fabricated on an AIS1316L stainless steel （SS） by using the surface mechanical rolling treatment （SMRT）. Reciprocating dry and oil-lubricated sliding tests of the GNG 316L SS in air at room temperature were conducted in comparison with the coarse-grained （CG） counterpart. Worn surface morphologies and subsurface microstructures were investigated for both 316L SS samples. 316L SS with a GNG surface layer shows a significantly improved wear resistance, especially under oil-lubricated condition. The notably wear resistance enhancement of the GNG 316L SS is attributed to the GNG surface layer with high strain accommodation ability and high hardness, which can reduce the wear volume in the running-in stage effectively.展开更多
The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top laye...The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.展开更多
Heavy ingots are widely used in many industrial fields. The coarse grains formed during the process of in- got solidification influence the properties and fracture behaviors of the final products. The coarse grain gro...Heavy ingots are widely used in many industrial fields. The coarse grains formed during the process of in- got solidification influence the properties and fracture behaviors of the final products. The coarse grain growth was simulated under different thermal gradients. A 30Cr2Ni4MoV steel ingot was melted in a cubic crucible with dimen-sions of 15 cm×10 cm×23 cm, and the cooling conditions on each side of the crucible were controlled by different thermal curves. The influences of thermal gradients and rotational flows on grain growth in heavy steel ingots were then investigated both numerically and experimentally. The results showed that when the amplitude of the rotation angle was 60°, the metal was solidified under a reciprocating horizontal rotational condition when the angular velocity was 10 （°）/s or 20 （°）/s. As the thermal gradient increased, the lengths of the primary columnar grains in- creased, and the diameters of equiaxed grains decreased. When the direction of flow rotation was perpendicular to the direction of grain growth, the columnar grain zone was nearly eliminated, and the average diameter of equiaxed grains was 0.5 mm.展开更多
Gradient ultra-fine grained surface layer in 6063 aluminum alloy was obtained by means of a novel surface self-nanocrystallization technique,namely rotational accelerated shot peening(RASP)treatment.The average grain ...Gradient ultra-fine grained surface layer in 6063 aluminum alloy was obtained by means of a novel surface self-nanocrystallization technique,namely rotational accelerated shot peening(RASP)treatment.The average grain sizes along the vertical section vary from hundreds of nanometers in the top surface to micrometers in the matrix.By using orthogonal experimental design to compare roughness values and hardness values,we synthesized the processing parameters to obtain sample of smaller roughness values and higher hardness.展开更多
Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experi...Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experiments and atomic simulations,we show that a typical intermetallic TiAl alloy with gra-dient structure has a significant strengthening effect both at room temperature and high temperatures.The room-temperature compressive strength of TiAl alloys with gradient grain obtained by additive man-ufacturing is 2.57 GPa,which is∼2.7 times as strong as that with equiaxed grain.The strengthening effect is attributed to more sessile dislocations in gradient structure caused by the intersections of mul-tiple slip systems in gradient grain.More importantly,the strengthening effect is still effective at high temperatures and the compressive strength is 1.28 GPa at 750°C.The simulation results show that this strengthening effect is due to the increased Hirth dislocation at high temperatures.This study expands the applications of TiAl alloys for load-bearing structures and provides a new strategy for improving the strength of intermetallic compounds at both room temperature and high temperatures.展开更多
In this study, the gradient grain induced by punching deformation and recovery treatment on a cupronickel alloy surface sample were investigated, and their effects on corrosion resistance were measured by atom force m...In this study, the gradient grain induced by punching deformation and recovery treatment on a cupronickel alloy surface sample were investigated, and their effects on corrosion resistance were measured by atom force microscopy(AFM), X-ray diffraction(XRD),electrochemical measurement, electron work function(EWF), and contact electrical resistance(CER). The cupronickel alloy surface experienced punching deformation for 60 min and recovery at 300 ℃ for 1 h to produce gradient surface. The grain size measured by XRD is bigger than that measured by AFM, due to X-ray intensity of95 % produced at the depth of 12-20 μm for the crystal planes of(111),(200), and(220). The gradient grain surface, compared to the original surface, shows a 13.7-fold decrease in passivation current density(i), and corrosion potential(Ec) increases by approximately 9.8 %. These results are attributable to the increase in EWF and formation of passivation film with better adhesion and compactness after treatment.展开更多
The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation （PFSD） processing were investigated. In each case...The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation （PFSD） processing were investigated. In each case, the deformation microstructure was characterized and the hardness of the treated surface layer was measured to evaluate its strength. The results indicated that the thickness of the deformed layer and the hardness at any depth increased with increasing normal stress. A smaller steel platen surface roughness resulted in less microstruc- tural refinement, whereas the microstructural refinement was enhanced by decreasing the surface roughness of the Cu sample. In the case of a very large initial grain size （d 〉 10 mm）, a sharper transition from fine-grain microstructure to undeformed material was obtained in the treated surface layer after PFSD processing.展开更多
Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-fr...Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-free steel by means of surface mechanical rolling treatment. Microstructural observations demonstrated that the average lamellar thickness is about 80 nm in the topmost surface layer and increases with increasing depth. High thermal stability was confirmed in the GNL surface layer after annealing at 500℃. Diffusion measurements showed that effective diffusivity of Cr in GNL layer is 4–6 orders of magnitude higher than lattice diffusivity within the temperature range from 400 to 500℃. This might be attributed to numerous LAGBs or dislocation structures with a higher energy state in the GNL surface layer. This work demonstrates the possibility to advanced chromizing(or other surface alloying)processes of steels with formation of GNL surface layer, so that a thicker alloyed surface layer with a stable nanostructure is achieved.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52122102 and 523B2003).
文摘Achieving high yield strength and ductility in alloys remains a significant challenge in structural materials.In this study,combined nanoprecipitation and gradient grain structure were introduced into a Co-Cr-Ni-based multi-principal element alloy(MPEA)using surface mechanical attrition treatment(SMAT).The multi-scale composite structure,featuring grain sizes refined from∼43.6μm to∼24.3 nm at the topmost surface and high-density L1_(2)nanoprecipitates within the grains,results in a substantial tensile strength of 1733 MPa and a well-maintained ductility of∼23%.The alloy with low local stacking fault energy provides sufficient flow stress to reach the critical value for twinning,a phenomenon rarely observed in MPEAs with high-density L1_(2)nanoprecipitates under quasi-static tensile conditions.The formation of nanotwins further facilitates additional strain hardening,enhancing mechanical performance at ultrahigh strength levels.This work offers significant insights into the deformation behavior of gradient-structured materials with high-density nanoprecipitates.
基金Project(2014CB644003)supported by the National Basic Research Program of ChinaProject(51321003)supported by the National Natural Science Foundation of ChinaProject(B06025)supported by"111"Project of China
文摘Titanium with gradient nano-to-micron scale grains from surface to matrix was fabricated by surface mechanical grinding treatment(SMGT) at room temperature.The SMGT-treated titanium shows higher strength than that of as-received one,but moderate ductility between those of ultra-fine grained(UFG) and coarse-grained titanium.Tensile stress-strain curves of SMGT-treated titanium show double strain hardening regimes.The strain hardening rate(dσ/dε) decreases with increasing strain in tensile deformation.The high strain hardening rate at initial yielding is attributed to nano-to-micron-grained surface layer.The low strain hardening rate at large plastic strain regime primarily results from coarse-grained matrix.The SMGT-treated titanium shows a ductile fracture mode with a large number of dimples.The small size of dimples in the treated surface layer is due to the combination of the high strength and strain hardening exponent.The difference between dimple size in nano-to-micron-grained surface layer and coarse-grained matrix is discussed in terms of plastic zone size at the tip of crack in the SMGT-treated titanium.
基金the financial supports of the National Key R&D Program of China(No.2017YFA0204401)the National Natural Science Foundation(No.51231006)the Key Research Program of Chinese Academy of Sciences(No.KGZD-EW-T06)
文摘A gradient nano-grained （GNG） surface layer was fabricated on an AIS1316L stainless steel （SS） by using the surface mechanical rolling treatment （SMRT）. Reciprocating dry and oil-lubricated sliding tests of the GNG 316L SS in air at room temperature were conducted in comparison with the coarse-grained （CG） counterpart. Worn surface morphologies and subsurface microstructures were investigated for both 316L SS samples. 316L SS with a GNG surface layer shows a significantly improved wear resistance, especially under oil-lubricated condition. The notably wear resistance enhancement of the GNG 316L SS is attributed to the GNG surface layer with high strain accommodation ability and high hardness, which can reduce the wear volume in the running-in stage effectively.
基金Funded by the National National Natural Science Foundation of China(No.51505189)Open Project of Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment&Technology(No.FM-2015-5)
文摘The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.
基金Sponsored by National Basic Research Program of China(2011CB012900)
文摘Heavy ingots are widely used in many industrial fields. The coarse grains formed during the process of in- got solidification influence the properties and fracture behaviors of the final products. The coarse grain growth was simulated under different thermal gradients. A 30Cr2Ni4MoV steel ingot was melted in a cubic crucible with dimen-sions of 15 cm×10 cm×23 cm, and the cooling conditions on each side of the crucible were controlled by different thermal curves. The influences of thermal gradients and rotational flows on grain growth in heavy steel ingots were then investigated both numerically and experimentally. The results showed that when the amplitude of the rotation angle was 60°, the metal was solidified under a reciprocating horizontal rotational condition when the angular velocity was 10 （°）/s or 20 （°）/s. As the thermal gradient increased, the lengths of the primary columnar grains in- creased, and the diameters of equiaxed grains decreased. When the direction of flow rotation was perpendicular to the direction of grain growth, the columnar grain zone was nearly eliminated, and the average diameter of equiaxed grains was 0.5 mm.
基金funded by NSFC(Grant No.51301092)the National Key R&D Program of China(Grant No.2017YFA0204403)Open Research Fund of Science and Technology on High Strength Structural Materials Laboratory(No.O2016006).
文摘Gradient ultra-fine grained surface layer in 6063 aluminum alloy was obtained by means of a novel surface self-nanocrystallization technique,namely rotational accelerated shot peening(RASP)treatment.The average grain sizes along the vertical section vary from hundreds of nanometers in the top surface to micrometers in the matrix.By using orthogonal experimental design to compare roughness values and hardness values,we synthesized the processing parameters to obtain sample of smaller roughness values and higher hardness.
基金This research was supported by the National Natural Science Foundation of China(Nos.52174364,12202201,92163215,52101143,and 91860104)Natural Science Foundation of Jiangsu Province(Nos.BK20220918,BK20212009)+3 种基金Science Center for Gas Turbine Project(P2022-A-IV-001-003)China Postdoctoral Science Foundation(No.2021M691582)the Fundamental Research Funds for the Central Universities(Nos.30922010711 and 30922010202)Open Project Program of Key Laboratory of China North Engine Research Institute(No.6142212210103).
文摘Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experiments and atomic simulations,we show that a typical intermetallic TiAl alloy with gra-dient structure has a significant strengthening effect both at room temperature and high temperatures.The room-temperature compressive strength of TiAl alloys with gradient grain obtained by additive man-ufacturing is 2.57 GPa,which is∼2.7 times as strong as that with equiaxed grain.The strengthening effect is attributed to more sessile dislocations in gradient structure caused by the intersections of mul-tiple slip systems in gradient grain.More importantly,the strengthening effect is still effective at high temperatures and the compressive strength is 1.28 GPa at 750°C.The simulation results show that this strengthening effect is due to the increased Hirth dislocation at high temperatures.This study expands the applications of TiAl alloys for load-bearing structures and provides a new strategy for improving the strength of intermetallic compounds at both room temperature and high temperatures.
基金financially supported by the National Natural Science Foundation of China (No.51301086)the Natural Science Foundation of Jiangsu Province (No. BK20130738)Jiangsu Province Key Laboratory of High-End Structural Materials Foundation(No.hsm1405)
文摘In this study, the gradient grain induced by punching deformation and recovery treatment on a cupronickel alloy surface sample were investigated, and their effects on corrosion resistance were measured by atom force microscopy(AFM), X-ray diffraction(XRD),electrochemical measurement, electron work function(EWF), and contact electrical resistance(CER). The cupronickel alloy surface experienced punching deformation for 60 min and recovery at 300 ℃ for 1 h to produce gradient surface. The grain size measured by XRD is bigger than that measured by AFM, due to X-ray intensity of95 % produced at the depth of 12-20 μm for the crystal planes of(111),(200), and(220). The gradient grain surface, compared to the original surface, shows a 13.7-fold decrease in passivation current density(i), and corrosion potential(Ec) increases by approximately 9.8 %. These results are attributable to the increase in EWF and formation of passivation film with better adhesion and compactness after treatment.
基金the Danish National Research Foundation (Grant No. DNRF86-5)the National Natural Science Foundation of China (Grant Nos. 51261130091 and 51171085) to the Danish–Chinese Center for Nanometals
文摘The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation （PFSD） processing were investigated. In each case, the deformation microstructure was characterized and the hardness of the treated surface layer was measured to evaluate its strength. The results indicated that the thickness of the deformed layer and the hardness at any depth increased with increasing normal stress. A smaller steel platen surface roughness resulted in less microstruc- tural refinement, whereas the microstructural refinement was enhanced by decreasing the surface roughness of the Cu sample. In the case of a very large initial grain size （d 〉 10 mm）, a sharper transition from fine-grain microstructure to undeformed material was obtained in the treated surface layer after PFSD processing.
基金Financial supports from the National Key Research and Development Program of China (No. 2017YFA0204401)Shenyang National Laboratory for Materials Science (No. 2015RP04)
文摘Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-free steel by means of surface mechanical rolling treatment. Microstructural observations demonstrated that the average lamellar thickness is about 80 nm in the topmost surface layer and increases with increasing depth. High thermal stability was confirmed in the GNL surface layer after annealing at 500℃. Diffusion measurements showed that effective diffusivity of Cr in GNL layer is 4–6 orders of magnitude higher than lattice diffusivity within the temperature range from 400 to 500℃. This might be attributed to numerous LAGBs or dislocation structures with a higher energy state in the GNL surface layer. This work demonstrates the possibility to advanced chromizing(or other surface alloying)processes of steels with formation of GNL surface layer, so that a thicker alloyed surface layer with a stable nanostructure is achieved.
