Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca(AZX211,in wt.%)plates with a rare earth-like texture.Varying amounts of deformation were applied along the rolling direction(RD)a...Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca(AZX211,in wt.%)plates with a rare earth-like texture.Varying amounts of deformation were applied along the rolling direction(RD)and transverse direction(TD)of AZX211 alloy in order to modify its mechanical proper-ties at room temperature.The results demonstrate that pre-stretching treatment effectively enhances the yield strength(YS),especially along the RD.The strengthening mechanism is attributed to the production of a large number of dislocations and sub-grain boundaries,but the work-hardening ability of the plate will be greatly weakened.Additionally,annealing treatment substantially improves the plasticity and in-plane anisotropy and restores the work-hardening ability.The notable distinction in the pre-stretching process between different directions lies in the underlying deformation mechanism.In case of RD,de-formation is predominantly governed by the slip mechanism of{0002}{11−20}basal slip and{10−10}{11−20}prismatic slip,while along the TD,deformation is primarily controlled by{0002}{11−20}basal slip without significant twinning deformation.When a 6%pre-stretching is conducted,the initial rare earth-like texture of the sample transforms into a symmetrically distributed double-peak basal texture,accompanied by grain refinement.This texture transformation is chiefly due to the dominance of{0002}{11−20}basal slip-driven deformation.Moreover,the annealed sample maintains a strong basal texture,owing to strain-induced recrystallization.展开更多
The elastic constants,ideal tensile strength(ITS),stacking fault energy(SFE),lattice constant and magnetic moment of FeMnCoCrNi high entropy alloys with varying Co and Cr contents at 0 and 300 K were systematically in...The elastic constants,ideal tensile strength(ITS),stacking fault energy(SFE),lattice constant and magnetic moment of FeMnCoCrNi high entropy alloys with varying Co and Cr contents at 0 and 300 K were systematically investigated by first-principle calculations.For the alloys with Co substitution for Ni,at both temperatures the elastic stability of the face-centered cubic(fcc)phase,bulk elastic modulus(B),Young’s modulus(E),shear modulus(G)and ITS increase monotonically with increasing Co content.However,the Cauchy pressure(Cp),Pugh ratio(B/G),Poisson ratio(v),Zener anisotropy ratio(AZ)and elastic anisotropy ratio(AVR)decrease monotonically.The SFE also decreases with the increase of Co,resulting in the change of plastic deformation mechanism from dislocation slip to mechanical twinning,and then to hcp-martensitic transformation.This elucidates the underlying mechanism of the effect of Co addition on the strength and micromechanical behavior of FeMnCoCrNi alloys.Compared with Co,the Cr substitution for Ni leads to the more complex change of elastic constants and ITS.The increase of Cr shows the similar effect on SFE and deformation mechanism as that of Co.The variation of valence electron concentration and magnetism affect the SFE.The increase of either Co or Cr leads to the reduced magnetic moments of Fe and Mn.This could be responsible for the monotonic decrease of both lattice constant and SFE as the Co content increases.However,for the Cr addition case,multiple factors may affect the evolution of lattice constant and SFE.These findings shed light on the deformation mechanism of the alloys with different compositions.展开更多
The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction...The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.展开更多
The retrogression and re-aging(RRA)processes,aimed mainly at tailoring intergranular precipitates,could significantly improve the corrosion resistance(i.e.,stress corrosion cracking resistance)without considerably dec...The retrogression and re-aging(RRA)processes,aimed mainly at tailoring intergranular precipitates,could significantly improve the corrosion resistance(i.e.,stress corrosion cracking resistance)without considerably decreasing the strength,which signifies that an efficient control of the size,distribution and evolution of intergranular and intragranular precipitates becomes critical for the integrated properties of the(mid-)thick high-strength Al alloy plates.Compared to RRA process with retrogression at200℃ (T77),this study investigated the impact of a modified RRA process(MT77)with lower retrogression temperatures(155-175℃ )and first-stage under-aging on the properties of a high-strength AA7050 Al alloy,in combination with detailed precipitate characterization.The study showed that the strength/microhardness of the RRA-treated alloys decreased with raising retrogression temperature and/or prolonging retrogression time,along with the increased electrical conductivity.The rapid responsiveness of microstructure/property typical of retrogression at 200℃ was obviously postponed or decreased by using MT77 process with longer retrogression time that was more suitable for treating the(mid-)thick plates.On the other hand,higher retrogression temperature facilitated more intragranularηprecipitates,coarse intergranular precipitates and wide precipitate free zones,which prominently increased the electrical conductivity alongside a considerable strength loss as compared to the MT77-treated alloys.With the preferred MT77 process,the high strength approaching T6 level as well as good corrosion resistance was achieved.However,though a relatively homogeneous through-thickness strength was obtained,some small discrepancies of properties between the central and surface areas of an 86-mm thick 7050 Al alloy plate were observed,possibly related to the quenching sensitivity.The precipitate evolution and mechanistic connection to the properties were discussed and reviewed for high-strength Al alloys along with suggestions for further RRA optimization.展开更多
The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechani...The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space.In this work,we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations.The negative Gibbs free energy difference△E_(FCC-BCC)between the face-centered cubic(FCC)and body-centered cubic(BCC)phases,the enhancement of shear modulus G and the decline of stacking fault energy(SFE)γ_(isf)are combined as three requisites to improve the FCC phase stability,yield strength,deformation mechanisms,work-hardening ability and ductility in the criterion.The effects of chemical composition on△E_(FCC-BCC),G andγisf were investigated with the first principles calculations for Co_(x)Cr_(33)Ni_(67-x),Co_(33)Cr_(y)Ni_(67-y)and Co_(z)Cr_(66-z)Ni_(34)(0≤x,y≤67 and 0≤z≤66)alloys.Based on the essential criterion and the calculation results,the composition space that displays the neg-ative Gibbs free energy difference△E_(FCC-BCC),highest shear modulus G and lowest SFEγ_(isf)was screened with the target on the combination of high strength and excellent ductility.In this context,the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.%Co,30 at.%-35 at.%Cr and 0 at.%-6 at.%Ni,which coincides well with the previous experimental evidence for Co_(55)Cr_(40)Ni_(5)alloys.The valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data,which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.展开更多
The particle raft is a two-dimensional condensed soft matter,which is composed of hydrophobic solid particles floating on a liquid surface.In this study,we have realized to conduct tension and shear experiments on the...The particle raft is a two-dimensional condensed soft matter,which is composed of hydrophobic solid particles floating on a liquid surface.In this study,we have realized to conduct tension and shear experiments on the particle raft by using the self-assembled loading device.The crack initiation and propagation are observed by the camera,and the curve of the non-dimensional force with respect to the displacement is given.These experimental results have been compared with the particle flow code 3D(PFC3D)simulation,and they are in excellent agreement.It indicates that the particle raft possesses mechanical properties between solid and liquid.These findings provide some inspirations on engineering new devices and new materials at the microscale.展开更多
This study investigates the influence of varying rolling reduction on the evolution of microstructure and mechanical properties of Mg–10Gd(in wt%)alloys by caliber rolling(CR).By increasing the rolling reduction from...This study investigates the influence of varying rolling reduction on the evolution of microstructure and mechanical properties of Mg–10Gd(in wt%)alloys by caliber rolling(CR).By increasing the rolling reduction from 45%to 65%,a uniform bimodal structure is obtained in which coarse grains(CGs)larger than 10μm are surrounded by fine grains(FGs).The Mg–Gd alloy subjected to 65%reduction exhibits superior mechanical properties,i.e.yield strength(YS)of~424 MPa,ultimate tensile strength(UTS)of~500 MPa and elongation(El.)of~3.3%.The synergistic improvement in strength and ductility is primarily attributed to the combined effects of low-angle grain boundary(LAGB)strengthening,precipitation strengthening,and the coordinated deformation exhibited by the bimodal structure.In addition,caliber rolling also provides a novel approach for the design of Mg alloys with uniform bimodal structures that exhibit both high strength and ductility.展开更多
基金supported by the National Natural Science Foundation of China(No.52001106)Hebei province(No.E2022202158).
文摘Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca(AZX211,in wt.%)plates with a rare earth-like texture.Varying amounts of deformation were applied along the rolling direction(RD)and transverse direction(TD)of AZX211 alloy in order to modify its mechanical proper-ties at room temperature.The results demonstrate that pre-stretching treatment effectively enhances the yield strength(YS),especially along the RD.The strengthening mechanism is attributed to the production of a large number of dislocations and sub-grain boundaries,but the work-hardening ability of the plate will be greatly weakened.Additionally,annealing treatment substantially improves the plasticity and in-plane anisotropy and restores the work-hardening ability.The notable distinction in the pre-stretching process between different directions lies in the underlying deformation mechanism.In case of RD,de-formation is predominantly governed by the slip mechanism of{0002}{11−20}basal slip and{10−10}{11−20}prismatic slip,while along the TD,deformation is primarily controlled by{0002}{11−20}basal slip without significant twinning deformation.When a 6%pre-stretching is conducted,the initial rare earth-like texture of the sample transforms into a symmetrically distributed double-peak basal texture,accompanied by grain refinement.This texture transformation is chiefly due to the dominance of{0002}{11−20}basal slip-driven deformation.Moreover,the annealed sample maintains a strong basal texture,owing to strain-induced recrystallization.
基金financially supported by the National Natural Science Foundation of China(Nos.51922026 and 51571057)the Fundamental Research Funds for the Central Universities(Nos.N2002005 and N2007011)the Liaoning Natural Science Foundation(No.20180510010)。
文摘The elastic constants,ideal tensile strength(ITS),stacking fault energy(SFE),lattice constant and magnetic moment of FeMnCoCrNi high entropy alloys with varying Co and Cr contents at 0 and 300 K were systematically investigated by first-principle calculations.For the alloys with Co substitution for Ni,at both temperatures the elastic stability of the face-centered cubic(fcc)phase,bulk elastic modulus(B),Young’s modulus(E),shear modulus(G)and ITS increase monotonically with increasing Co content.However,the Cauchy pressure(Cp),Pugh ratio(B/G),Poisson ratio(v),Zener anisotropy ratio(AZ)and elastic anisotropy ratio(AVR)decrease monotonically.The SFE also decreases with the increase of Co,resulting in the change of plastic deformation mechanism from dislocation slip to mechanical twinning,and then to hcp-martensitic transformation.This elucidates the underlying mechanism of the effect of Co addition on the strength and micromechanical behavior of FeMnCoCrNi alloys.Compared with Co,the Cr substitution for Ni leads to the more complex change of elastic constants and ITS.The increase of Cr shows the similar effect on SFE and deformation mechanism as that of Co.The variation of valence electron concentration and magnetism affect the SFE.The increase of either Co or Cr leads to the reduced magnetic moments of Fe and Mn.This could be responsible for the monotonic decrease of both lattice constant and SFE as the Co content increases.However,for the Cr addition case,multiple factors may affect the evolution of lattice constant and SFE.These findings shed light on the deformation mechanism of the alloys with different compositions.
基金financial support from Natural Sciences and Engineering ResearchCouncil(NSERC)(NSERC EGP 501335-16) along with the donated CSA cement
文摘The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.
基金financial support from the Constructed Project for Key Laboratory of Beijing,China(No.BJSJ2019004)the State Key Laboratory for Advanced Metals and Materials of China(No.2018Z-23)+2 种基金the Major State Research and Development Program of China(No.2016YFB0300801)the National Natural Science Foundation of China(No.51401016)the supports from International S&T Cooperation Projects of Nanjing,China(No.201818014)。
文摘The retrogression and re-aging(RRA)processes,aimed mainly at tailoring intergranular precipitates,could significantly improve the corrosion resistance(i.e.,stress corrosion cracking resistance)without considerably decreasing the strength,which signifies that an efficient control of the size,distribution and evolution of intergranular and intragranular precipitates becomes critical for the integrated properties of the(mid-)thick high-strength Al alloy plates.Compared to RRA process with retrogression at200℃ (T77),this study investigated the impact of a modified RRA process(MT77)with lower retrogression temperatures(155-175℃ )and first-stage under-aging on the properties of a high-strength AA7050 Al alloy,in combination with detailed precipitate characterization.The study showed that the strength/microhardness of the RRA-treated alloys decreased with raising retrogression temperature and/or prolonging retrogression time,along with the increased electrical conductivity.The rapid responsiveness of microstructure/property typical of retrogression at 200℃ was obviously postponed or decreased by using MT77 process with longer retrogression time that was more suitable for treating the(mid-)thick plates.On the other hand,higher retrogression temperature facilitated more intragranularηprecipitates,coarse intergranular precipitates and wide precipitate free zones,which prominently increased the electrical conductivity alongside a considerable strength loss as compared to the MT77-treated alloys.With the preferred MT77 process,the high strength approaching T6 level as well as good corrosion resistance was achieved.However,though a relatively homogeneous through-thickness strength was obtained,some small discrepancies of properties between the central and surface areas of an 86-mm thick 7050 Al alloy plate were observed,possibly related to the quenching sensitivity.The precipitate evolution and mechanistic connection to the properties were discussed and reviewed for high-strength Al alloys along with suggestions for further RRA optimization.
基金We sincerely acknowledge the support of the work by the Na-tional Natural Science Foundation of China(NSFC)(Nos.52130002,52071316,51871223,51771206 and 51571198)the Youth Innova-tion Promotion Association CAS(No.2021192)the KC Wong Education Foundation(No.GJTD-2020-09).
文摘The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials innovation.However,designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space.In this work,we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations.The negative Gibbs free energy difference△E_(FCC-BCC)between the face-centered cubic(FCC)and body-centered cubic(BCC)phases,the enhancement of shear modulus G and the decline of stacking fault energy(SFE)γ_(isf)are combined as three requisites to improve the FCC phase stability,yield strength,deformation mechanisms,work-hardening ability and ductility in the criterion.The effects of chemical composition on△E_(FCC-BCC),G andγisf were investigated with the first principles calculations for Co_(x)Cr_(33)Ni_(67-x),Co_(33)Cr_(y)Ni_(67-y)and Co_(z)Cr_(66-z)Ni_(34)(0≤x,y≤67 and 0≤z≤66)alloys.Based on the essential criterion and the calculation results,the composition space that displays the neg-ative Gibbs free energy difference△E_(FCC-BCC),highest shear modulus G and lowest SFEγ_(isf)was screened with the target on the combination of high strength and excellent ductility.In this context,the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.%Co,30 at.%-35 at.%Cr and 0 at.%-6 at.%Ni,which coincides well with the previous experimental evidence for Co_(55)Cr_(40)Ni_(5)alloys.The valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data,which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.
基金This work was supported by the National Natural Science Foundation of China(Grants 11672335 and 1197237)Open Fund of State key Laboratory Breeding Base for Mining Disaster Prevention and Control(MDPC201601)+1 种基金the Key R&D Program in Shandong Province(Grant 2019GHZ001)State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology(Grant MDPC201601).
文摘The particle raft is a two-dimensional condensed soft matter,which is composed of hydrophobic solid particles floating on a liquid surface.In this study,we have realized to conduct tension and shear experiments on the particle raft by using the self-assembled loading device.The crack initiation and propagation are observed by the camera,and the curve of the non-dimensional force with respect to the displacement is given.These experimental results have been compared with the particle flow code 3D(PFC3D)simulation,and they are in excellent agreement.It indicates that the particle raft possesses mechanical properties between solid and liquid.These findings provide some inspirations on engineering new devices and new materials at the microscale.
基金financial support from the National Natural Science Foundation of China(51701060,52001106)Hebei Province(E2022202158),the foundation of the Strengthening Program(2019-JCJQ-142-00)。
文摘This study investigates the influence of varying rolling reduction on the evolution of microstructure and mechanical properties of Mg–10Gd(in wt%)alloys by caliber rolling(CR).By increasing the rolling reduction from 45%to 65%,a uniform bimodal structure is obtained in which coarse grains(CGs)larger than 10μm are surrounded by fine grains(FGs).The Mg–Gd alloy subjected to 65%reduction exhibits superior mechanical properties,i.e.yield strength(YS)of~424 MPa,ultimate tensile strength(UTS)of~500 MPa and elongation(El.)of~3.3%.The synergistic improvement in strength and ductility is primarily attributed to the combined effects of low-angle grain boundary(LAGB)strengthening,precipitation strengthening,and the coordinated deformation exhibited by the bimodal structure.In addition,caliber rolling also provides a novel approach for the design of Mg alloys with uniform bimodal structures that exhibit both high strength and ductility.
