One of the bottleneck issues for commercial scale-up of Ti additive manufacturing lies in high cost of raw material, i.e. the spherical Ti powder that is often made by gas atomization. In this study, we address this s...One of the bottleneck issues for commercial scale-up of Ti additive manufacturing lies in high cost of raw material, i.e. the spherical Ti powder that is often made by gas atomization. In this study, we address this significant issue by way of powder modification & ball milling processing, which shows that it is possible to produce printable Ti powders based on ultra- low cost, originally unprintable hydrogenation-dehydrogenation (HDH) Ti powder. It is also presented that the as-printed Ti using the modified powder exhibits outstanding mechanical properties, showing a combination of excellent fracture strength (~895 MPa) and high ductility (~19.0% elongation).展开更多
In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and...In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and annealing processes.The recrystallized sample is revealed to exhibit an excellent combination of strength and ductility over a wide temperature range of 4.2–293 K.With decreasing temperature from 293 to 77 K,the ductility and ultimate tensile strength(UTS)gradually increase by 30% to 95% and 137% to 1020 MPa,respectively.At the lowest temperature of 4.2 K,the ductility keeps 65% and the UTS increases by 200% to 1300 MPa,which exceed those published in the literature,including conventional 300 series stainless steels.Detailed microstructural analyses of this alloy reveal a change of deformation mechanisms from dislocation slip and nano-twinning at 293 K to nano-phase transformation at 4.2 K.The cooperation and competition of multiple nano-twinning and nano-phase transformation are responsible for the superior tensile properties at cryogenic temperatures.Our study provides experimental evidence for potential cryogenic applications of HEAs.展开更多
A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid so...A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid solution and aging”process,the superfine(Fe,Ni)_(2)TiSi-L2_(1)particles densely precipitate within the ferritic grain and subsequently transform into the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase.In the meanwhile,the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase are also observed.These nanoscale microstructural evolutions result in a remarkable increase in hardness(100-300 HV)and severe embrittlement.When the“cold rolling and aging”process is used,the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening ef-fect.Superhigh yield strength of 1700 MPa with 4%elongation at break is achieved.This key improvement in mechanical properties is mainly attributed to the pre-cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary.These findings could shed light on the further exploration of the precipitation site via optimal processing strategies.展开更多
As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effect...As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effectively achieve ultra-high strength and maintain reliable ductility remains a challenge.Here,we report a study of doping extremely little boron to meet this target.We found that adding of 30 ppm boron into the heavy Ti and Al alloyed FCC FeCoNiCr high-entropy,(FeCoNiCr)_(88) Ti_(6) Al_(6) HEA(at.%)which is strengthened mainly by both coarse BCC-based(Ni,Co)_(2) TiAl Heusler and fine L12-type FCC-based(Ni,Co)_(3) TiAl precipitates and shows ultrahigh strength but poor ductility,could significantly change the original microstructure and consequently improve mechanical performance,owing to the well-known effect of boron on reducing the energy of grain boundaries.The boron addition can(1)eliminate microcavities formed at Heusler precipitate-matrix interfaces;(2)suppress the formation and segregation of coarse BCC Heusler precipitates;(3)promote the formation of L12 nanoparticles.This changes of microstructure substantially improve the tensile ductility more than by~86%and retain comparable or even better ultimate tensile strength.These findings may provide a simple and costless solution to produce heavy precipitation-strengthened HEAs with ultrahigh strength and prevent accidental brittleness.展开更多
Low ductility and strength are major bottlenecks against Mg alloys’wide applications.In this work,we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy,showing that it can ...Low ductility and strength are major bottlenecks against Mg alloys’wide applications.In this work,we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy,showing that it can be extruded at low temperatures(~250℃)and high speeds(~2 mm/s).After the extrusion,this alloy exhibits a substantially weakened basal texture,relatively small grain size,very high tensile elongation(~30%),and good strength.The origin of the considerably improved ductility was studied using a combination of three-dimensional atom probe tomography(3D-APT),transmission electron microscopy(TEM),electron backscattered diffraction(EBSD)in conjunction with surface slip trace analysis,in-situ synchrotron X-ray diffraction,and elasto-plastic self-consistent(EPSC)modeling.Co-segregation of Zn and Ca atoms at a grain boundary is observed and associated with texture weakening and grain boundary mediated plasticity,both improving the ductility.While basal slip and prismatic slip are identified as the dominant deformation systems in the alloy,the ratio between their slip resistances is substantially reduced relative to pure Mg and most other Mg alloys,significantly contributing to the improved ductility of the alloy.This Mg-Zn-Ca alloy exhibiting excellent mechanical properties and low fabrication cost is a promising candidate for industrial productions.展开更多
Redistribution of elements may take place in alloys during severe plastic deformation, which significantly alters the mechanical properties of the alloys. Therefore, comprehensive knowledge about deformationinduced re...Redistribution of elements may take place in alloys during severe plastic deformation, which significantly alters the mechanical properties of the alloys. Therefore, comprehensive knowledge about deformationinduced redistribution of elements has to be established. In the present paper, the distribution of Mg in an Al-Mg alloy processed by high pressure torsion was examined using atom probe tomography(APT).With crystallographic information extracted by APT data analysis, this research reveals that the movement of dislocations plays an important role in the formation of Mg-depletion zones in the deformed microstructure.展开更多
Single-phase Al-Mg alloys processed by severe plastic deformation(SPD)usually suffer from unsatisfactory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening...Single-phase Al-Mg alloys processed by severe plastic deformation(SPD)usually suffer from unsatisfactory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening.In the present work,an Al-7Mg alloy prepared by equal-channel angular pressing(ECAP)possessed markedly enhanced thermal stability upon annealing at moderate to high temperatures(200-275℃),compared with those ultrafine-grained dilute Al-Mg alloys with a uniform microstructure.The enhanced thermal stability is due primarily to the multimodal grain structure consisting of nano-,ultrafine-and micron-sized grains,strong segregation and/or clusters of Mg solute along grain boundaries(GBs),and Al_(3)Mg_(2)precipitates formed during annealing.First,extensive recovery predominates over recrystallization and consumes most of the stored energy in the ECAPed Al-7Mg alloy annealed at≤275℃,leading to the recrystallization and growth of nano/ultrafine grains being retarded or postponed.Moreover,Mg solute segregation and/or clusters along GBs of nano/ultrafine grains could further suppress grain growth via diminishing GB energy and dragging GBs efficiently.In addition,Al_(3)Mg_(2)precipitates formed with increasing annealing time could inhibit grain growth by pinning GBs.The present multimodal-grained Al-7Mg alloy with enhanced thermal stability is believed to be particularly attractive in potential engineering applications at moderate to high temperatures.展开更多
Understanding composition effects is crucial for alloy design and development. To date, there is a lack of research comprehensively addressing the effect of alloy composition on dynamic precipitation, segregation and ...Understanding composition effects is crucial for alloy design and development. To date, there is a lack of research comprehensively addressing the effect of alloy composition on dynamic precipitation, segregation and grain refinement under severe-plastic-deformation processing. This research investigates Al-x Si alloys with x = 0.1, 0.5 and 1.0 at.% Si processed by high pressure torsion(HPT) at room temperature by using transmission electron microscopy, transmission Kikuchi diffraction and atom probe tomography. The alloys exhibit interesting composition-dependent grain refinement and fast dynamic decomposition under HPT processing. Si atoms segregate at dislocations and Si precipitates form at grain boundaries(GBs) depending on the Si content of the alloys. The growth of Si precipitates consumes most Si atoms segregating at GBs, hence the size and distribution of the Si precipitates become predominant factors in controlling the grain size of the decomposed Al-Si alloys after HPT processing. The hardness of the Al-Si alloys is well correlated with a combination of grain-refinement strengthening and the decomposition-induced softening.展开更多
基金Shenzhen Science and Technology Innovation Commission (No. ZDSYS201703031748354)National Science Foundation of Guangdong Province (No. 2016A030313756)+1 种基金the Pico Center at SUSTech with support from the Presidential fund and Development and Reform Commission of Shenzhen Municipality (No. 2016-726)the Humboldt Research Fellowship for Experienced Researchers.
文摘One of the bottleneck issues for commercial scale-up of Ti additive manufacturing lies in high cost of raw material, i.e. the spherical Ti powder that is often made by gas atomization. In this study, we address this significant issue by way of powder modification & ball milling processing, which shows that it is possible to produce printable Ti powders based on ultra- low cost, originally unprintable hydrogenation-dehydrogenation (HDH) Ti powder. It is also presented that the as-printed Ti using the modified powder exhibits outstanding mechanical properties, showing a combination of excellent fracture strength (~895 MPa) and high ductility (~19.0% elongation).
基金financially supported by the National Key R&D Program of China(Nos.2021YFA1200203,2019YFA0209901)the National Natural Science Foundation of China(Nos.51971112,51822402 and 51225102)+1 种基金the Fundamental Research Funds for the Central Universities(No.30919011405)the LiaoNing Revitalization Talents Program(No.XLYC1807047).
文摘In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and annealing processes.The recrystallized sample is revealed to exhibit an excellent combination of strength and ductility over a wide temperature range of 4.2–293 K.With decreasing temperature from 293 to 77 K,the ductility and ultimate tensile strength(UTS)gradually increase by 30% to 95% and 137% to 1020 MPa,respectively.At the lowest temperature of 4.2 K,the ductility keeps 65% and the UTS increases by 200% to 1300 MPa,which exceed those published in the literature,including conventional 300 series stainless steels.Detailed microstructural analyses of this alloy reveal a change of deformation mechanisms from dislocation slip and nano-twinning at 293 K to nano-phase transformation at 4.2 K.The cooperation and competition of multiple nano-twinning and nano-phase transformation are responsible for the superior tensile properties at cryogenic temperatures.Our study provides experimental evidence for potential cryogenic applications of HEAs.
基金This work was financially funded by the National Natural Science Foundation of China(Nos.51971082 and 52001098)the National Post-doctoral Program for Innovative Talents(No.BX20200103)the China Post-doctoral Science Foundation(No.2020M681092).The authors would like to thank Dr.Ivan Povstugar at ZEA-。
文摘A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid solution and aging”process,the superfine(Fe,Ni)_(2)TiSi-L2_(1)particles densely precipitate within the ferritic grain and subsequently transform into the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase.In the meanwhile,the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase are also observed.These nanoscale microstructural evolutions result in a remarkable increase in hardness(100-300 HV)and severe embrittlement.When the“cold rolling and aging”process is used,the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening ef-fect.Superhigh yield strength of 1700 MPa with 4%elongation at break is achieved.This key improvement in mechanical properties is mainly attributed to the pre-cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary.These findings could shed light on the further exploration of the precipitation site via optimal processing strategies.
基金the National Natural Science Foundation of China(NSFC)under Grant Nos.51871178。
文摘As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effectively achieve ultra-high strength and maintain reliable ductility remains a challenge.Here,we report a study of doping extremely little boron to meet this target.We found that adding of 30 ppm boron into the heavy Ti and Al alloyed FCC FeCoNiCr high-entropy,(FeCoNiCr)_(88) Ti_(6) Al_(6) HEA(at.%)which is strengthened mainly by both coarse BCC-based(Ni,Co)_(2) TiAl Heusler and fine L12-type FCC-based(Ni,Co)_(3) TiAl precipitates and shows ultrahigh strength but poor ductility,could significantly change the original microstructure and consequently improve mechanical performance,owing to the well-known effect of boron on reducing the energy of grain boundaries.The boron addition can(1)eliminate microcavities formed at Heusler precipitate-matrix interfaces;(2)suppress the formation and segregation of coarse BCC Heusler precipitates;(3)promote the formation of L12 nanoparticles.This changes of microstructure substantially improve the tensile ductility more than by~86%and retain comparable or even better ultimate tensile strength.These findings may provide a simple and costless solution to produce heavy precipitation-strengthened HEAs with ultrahigh strength and prevent accidental brittleness.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0701203)the National Natural Science Foundation of China(Nos.51631006,51671127 and 51825101)+3 种基金sponsored by the Youth Cheung Kong Scholars Programthe Shanghai Rising-Star Programthe support provided by the U.S.National Science Foundation(No.OIA-1757371)Use of the Advanced Photon Source was supported by the United States Department of Energy,Office of Science,Office of Basic Energy Sciences(No.DE-AC02-06CH11357)。
文摘Low ductility and strength are major bottlenecks against Mg alloys’wide applications.In this work,we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy,showing that it can be extruded at low temperatures(~250℃)and high speeds(~2 mm/s).After the extrusion,this alloy exhibits a substantially weakened basal texture,relatively small grain size,very high tensile elongation(~30%),and good strength.The origin of the considerably improved ductility was studied using a combination of three-dimensional atom probe tomography(3D-APT),transmission electron microscopy(TEM),electron backscattered diffraction(EBSD)in conjunction with surface slip trace analysis,in-situ synchrotron X-ray diffraction,and elasto-plastic self-consistent(EPSC)modeling.Co-segregation of Zn and Ca atoms at a grain boundary is observed and associated with texture weakening and grain boundary mediated plasticity,both improving the ductility.While basal slip and prismatic slip are identified as the dominant deformation systems in the alloy,the ratio between their slip resistances is substantially reduced relative to pure Mg and most other Mg alloys,significantly contributing to the improved ductility of the alloy.This Mg-Zn-Ca alloy exhibiting excellent mechanical properties and low fabrication cost is a promising candidate for industrial productions.
基金funded by the financial support of the National Natural Science Foundation of China (No. 51571120)the support and the assistance of the Material Characterization and Research Center of Nanjing University of Science and Technology
文摘Redistribution of elements may take place in alloys during severe plastic deformation, which significantly alters the mechanical properties of the alloys. Therefore, comprehensive knowledge about deformationinduced redistribution of elements has to be established. In the present paper, the distribution of Mg in an Al-Mg alloy processed by high pressure torsion was examined using atom probe tomography(APT).With crystallographic information extracted by APT data analysis, this research reveals that the movement of dislocations plays an important role in the formation of Mg-depletion zones in the deformed microstructure.
基金financially supported by the National Natural Science Foundation of China(Nos.51922048,51790483 and 51871108)the Changjiang Scholars Program(No.T2017035)。
文摘Single-phase Al-Mg alloys processed by severe plastic deformation(SPD)usually suffer from unsatisfactory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening.In the present work,an Al-7Mg alloy prepared by equal-channel angular pressing(ECAP)possessed markedly enhanced thermal stability upon annealing at moderate to high temperatures(200-275℃),compared with those ultrafine-grained dilute Al-Mg alloys with a uniform microstructure.The enhanced thermal stability is due primarily to the multimodal grain structure consisting of nano-,ultrafine-and micron-sized grains,strong segregation and/or clusters of Mg solute along grain boundaries(GBs),and Al_(3)Mg_(2)precipitates formed during annealing.First,extensive recovery predominates over recrystallization and consumes most of the stored energy in the ECAPed Al-7Mg alloy annealed at≤275℃,leading to the recrystallization and growth of nano/ultrafine grains being retarded or postponed.Moreover,Mg solute segregation and/or clusters along GBs of nano/ultrafine grains could further suppress grain growth via diminishing GB energy and dragging GBs efficiently.In addition,Al_(3)Mg_(2)precipitates formed with increasing annealing time could inhibit grain growth by pinning GBs.The present multimodal-grained Al-7Mg alloy with enhanced thermal stability is believed to be particularly attractive in potential engineering applications at moderate to high temperatures.
基金funded by the financial support of the National Natural Science Foundation of China (No.51751120 and No.51604156)support and the assistance of Material Characterization and Research Center of Nanjing University of Science and Technology。
文摘Understanding composition effects is crucial for alloy design and development. To date, there is a lack of research comprehensively addressing the effect of alloy composition on dynamic precipitation, segregation and grain refinement under severe-plastic-deformation processing. This research investigates Al-x Si alloys with x = 0.1, 0.5 and 1.0 at.% Si processed by high pressure torsion(HPT) at room temperature by using transmission electron microscopy, transmission Kikuchi diffraction and atom probe tomography. The alloys exhibit interesting composition-dependent grain refinement and fast dynamic decomposition under HPT processing. Si atoms segregate at dislocations and Si precipitates form at grain boundaries(GBs) depending on the Si content of the alloys. The growth of Si precipitates consumes most Si atoms segregating at GBs, hence the size and distribution of the Si precipitates become predominant factors in controlling the grain size of the decomposed Al-Si alloys after HPT processing. The hardness of the Al-Si alloys is well correlated with a combination of grain-refinement strengthening and the decomposition-induced softening.