In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy,the chemical environment and structural ordering in liquid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular...In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy,the chemical environment and structural ordering in liquid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular dynamics simulation.In liquid Mg-rich Mg-Y alloys,the strong Mg-Y interaction is determined,which promotes the formation of fivefold symmetric local structure.For Mg-Zn alloys,the weak Mg-Zn interaction results in the fivefold symmetry weakening in the liquid structure.Due to the coexistence of Y and Zn,the strong attractive interaction is introduced in liquid Mg-Y-Zn ternary alloy,and contributes to the clustering of Mg,Y,Zn launched from Zn.What is more,the distribution of local structures becomes closer to that in pure Mg compared with that in binary Mg-Y and Mg-Zn alloys.These results should relate to the origins of the Y/Zn segregation zone and close-packed stacking mode in LPSO structure,which provides a new insight into the formation mechanism of LPSO structure at atomic level.展开更多
Response to isochronal annealing up to 440 ℃ of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy(PM)and extruded at 280 ℃ was studied by resistivity and microhardness measurement,diff...Response to isochronal annealing up to 440 ℃ of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy(PM)and extruded at 280 ℃ was studied by resistivity and microhardness measurement,differential scanning calorimetry(DSC)and microstructure investigation.Electrical resistivity was measured at 77 K and microhardness was measured at room temperature after each annealing step.DSC measurement was performed at various heating rates.Transmission and scanning electron microscopy and optical microscopy revealed ribbons of long-period ordered structure(LPSO)18R and planar defects within grain boundaries.Relatively high density of planar defects was found in grain interiors of the cast alloy with the grain size approximately 50μm.Well pronounced subgrains were observed in the PM prepared alloy.Secondary phase particles decorate grain boundaries in this alloy.Three precipitation processes were detected in the cast alloy during repeated isochronal annealing up to 440 ℃,whereas only one significant process was revealed in the PM alloy.These processes were identified as embedding of stacking faults by solutes,development and rearrangement(18R→14H)of LPSO phase and development of grain boundary particles.A coarsening of grain boundary particles rich in Y and Zn only proceeds in the PM alloy.Activation energies of the precipitation processes were determined.Microhardness exhibits good thermal stability against annealing up to 360 ℃ in the PM alloy.展开更多
Phase equilibria involving the long-period stacking ordered phases including 14 H,18 R and 10 H in the Mg-rich corner of the Mg-Y-Zn system at 400 and 500℃ have been experimentally investigated by using X-ray diffrac...Phase equilibria involving the long-period stacking ordered phases including 14 H,18 R and 10 H in the Mg-rich corner of the Mg-Y-Zn system at 400 and 500℃ have been experimentally investigated by using X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).The coexistence of 14 H and 18 R as well as 18 R and 10 H was confirmed from atomic scales.The phases 14 H,18 R and 10 H were all stable phases from 400 to 500℃.The experimentally proved three-phase equilibrium of14 H,18 R and α-Mg instead of 14 H,18 R and Mg_(24)Y_(5) were presented in the modified isothermal sections.The latter three-phase equilibrium was reported in the available literature.The modified isothe rmal sections are conducive to guide the composition design to obtain the alloys with favorable microstructure constituents and mechanical properties.展开更多
基金supported by National Natural Science Foundation of China,China(No.51901117,51801116)Youth Innovation and Technology Support Program of Shandong Provincial Colleges and Universities,China(No.2020KJA002)+2 种基金Youth Fund of Shandong Academy of Sciences,China(2020QN0021)Innovation Pilot Project for Fusion of Science,Education and Industry(International Cooperation)from Qilu University of Technology(Shandong Academy of Sciences),China(No.2020KJC-GH03)Several Policies on Promoting Collaborative Innovation and Industrialization of Achievements in Universities and Research Institutes,China(No.2019GXRC030)。
文摘In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy,the chemical environment and structural ordering in liquid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular dynamics simulation.In liquid Mg-rich Mg-Y alloys,the strong Mg-Y interaction is determined,which promotes the formation of fivefold symmetric local structure.For Mg-Zn alloys,the weak Mg-Zn interaction results in the fivefold symmetry weakening in the liquid structure.Due to the coexistence of Y and Zn,the strong attractive interaction is introduced in liquid Mg-Y-Zn ternary alloy,and contributes to the clustering of Mg,Y,Zn launched from Zn.What is more,the distribution of local structures becomes closer to that in pure Mg compared with that in binary Mg-Y and Mg-Zn alloys.These results should relate to the origins of the Y/Zn segregation zone and close-packed stacking mode in LPSO structure,which provides a new insight into the formation mechanism of LPSO structure at atomic level.
基金Project(BK20160869)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(GY12015009)supported by the Nantong Science and Technology Program,China+1 种基金Project(2015B01314)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51501039)supported by the National Natural Science Foundation of China
基金the Czech Science Foundation(GACR),project No.16-12828S is also gratefully acknowledged.
文摘Response to isochronal annealing up to 440 ℃ of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy(PM)and extruded at 280 ℃ was studied by resistivity and microhardness measurement,differential scanning calorimetry(DSC)and microstructure investigation.Electrical resistivity was measured at 77 K and microhardness was measured at room temperature after each annealing step.DSC measurement was performed at various heating rates.Transmission and scanning electron microscopy and optical microscopy revealed ribbons of long-period ordered structure(LPSO)18R and planar defects within grain boundaries.Relatively high density of planar defects was found in grain interiors of the cast alloy with the grain size approximately 50μm.Well pronounced subgrains were observed in the PM prepared alloy.Secondary phase particles decorate grain boundaries in this alloy.Three precipitation processes were detected in the cast alloy during repeated isochronal annealing up to 440 ℃,whereas only one significant process was revealed in the PM alloy.These processes were identified as embedding of stacking faults by solutes,development and rearrangement(18R→14H)of LPSO phase and development of grain boundary particles.A coarsening of grain boundary particles rich in Y and Zn only proceeds in the PM alloy.Activation energies of the precipitation processes were determined.Microhardness exhibits good thermal stability against annealing up to 360 ℃ in the PM alloy.
基金National Key Research and Development Program of China (No.2016YFB0701201)the National Natural Science Foundation of China (No.51571019) for the financial supports。
文摘Phase equilibria involving the long-period stacking ordered phases including 14 H,18 R and 10 H in the Mg-rich corner of the Mg-Y-Zn system at 400 and 500℃ have been experimentally investigated by using X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).The coexistence of 14 H and 18 R as well as 18 R and 10 H was confirmed from atomic scales.The phases 14 H,18 R and 10 H were all stable phases from 400 to 500℃.The experimentally proved three-phase equilibrium of14 H,18 R and α-Mg instead of 14 H,18 R and Mg_(24)Y_(5) were presented in the modified isothermal sections.The latter three-phase equilibrium was reported in the available literature.The modified isothe rmal sections are conducive to guide the composition design to obtain the alloys with favorable microstructure constituents and mechanical properties.
