The knowledge of the equation of state(EOS)and the compressibility of a solid are of central importance for the understanding of the behavior and the application of a condensed matter.The compression behavior of Zr41T...The knowledge of the equation of state(EOS)and the compressibility of a solid are of central importance for the understanding of the behavior and the application of a condensed matter.The compression behavior of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass(BMG)is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with synchrotron radiation.A model of basic cell volume has been established and the equation of state of BMG is determined by the calculation of radial distribution function.The experimental results indicate that the BMG contains a large amount of vacancy-like free volume.Low pressure(below 7 GPa)induces the collapse of the free volume to some extent and structure relaxation in the BMG.展开更多
The crystallization kinetics of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass has been studied by using DSC and XRD. The results show that two exothermal peaks are observed when the alloy is heated to 500?℃, ...The crystallization kinetics of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass has been studied by using DSC and XRD. The results show that two exothermal peaks are observed when the alloy is heated to 500?℃, one peak results dominantly from the formation of Ti 2Ni ( α phase transition), the other peak is mainly due to the formation of Zr 2Cu ( β phase transition). At the beginning of the crystallization, the activation energy of the α phase is smaller, and it increases with increasing crystallized fraction ( x c). When x c increases to 90%, the crystallization activation energy shows the largest value (220?kJ/mol). The crystallization activation energy of the β phase remains about 227?kJ/mol, as it’s crystallized fraction is below 60%, and then it increases with increasing crystallized fraction, and shows the largest activation energy of 257?kJ/mol, as the x c is 65%.展开更多
Glass-forming ability is a long-standing concern in the field of metallic glasses(MGs),which greatly limits their maximum casting size and extensive applications.In this work,we report an ultrasonic-assisted rapid col...Glass-forming ability is a long-standing concern in the field of metallic glasses(MGs),which greatly limits their maximum casting size and extensive applications.In this work,we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives.MGs with various compositions are welded together under a 20,000-Hz highfrequency ultrasonic vibration without losing their amorphous nature.The ultrasonic technology offers the advantages of rapid bonding(<1 s)at low temperature(near room temperature)and low stress(<1 MPa).According to the phenomenon observed in the experiment,the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer,and the ultrasonic vibration accelerates the atomic-diffusion process.Finally,stable bonding of the MG interface is realized.This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.展开更多
Based on irreducible representations(or symmetry eigenvalues) and compatibility relations(CR), a material can be predicted to be a topological/trivial insulator(satisfying CR) or a topological semimetal(violating CR)....Based on irreducible representations(or symmetry eigenvalues) and compatibility relations(CR), a material can be predicted to be a topological/trivial insulator(satisfying CR) or a topological semimetal(violating CR). However, Weyl semimetals(WSMs) usually go beyond this symmetry-based strategy. In other words, Weyl nodes could emerge in a material, no matter if its occupied bands satisfy CR, or if the symmetry indicators are zero. In this work, we propose a new topological invariant v for the systems with S4 symmetry(i.e., the improper rotation S_(4)(≡IC_(4z)) is a proper fourfold rotation(C_(4z)) followed by inversion(I)), which can be used to diagnose the WSM phase. Moreover, v can be easily computed through the onedimensional Wilson-loop technique. By applying this method to the high-throughput screening in our first-principles calculations, we predict a lot of WSMs in both nonmagnetic and magnetic compounds.Various interesting properties(e.g., magnetic frustration effects, superconductivity and spin-glass order,etc.) are found in predicted WSMs, which provide realistic platforms for future experimental study of the interplay between Weyl fermions and other exotic states.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant No.10004014).
文摘The knowledge of the equation of state(EOS)and the compressibility of a solid are of central importance for the understanding of the behavior and the application of a condensed matter.The compression behavior of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass(BMG)is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with synchrotron radiation.A model of basic cell volume has been established and the equation of state of BMG is determined by the calculation of radial distribution function.The experimental results indicate that the BMG contains a large amount of vacancy-like free volume.Low pressure(below 7 GPa)induces the collapse of the free volume to some extent and structure relaxation in the BMG.
文摘The crystallization kinetics of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass has been studied by using DSC and XRD. The results show that two exothermal peaks are observed when the alloy is heated to 500?℃, one peak results dominantly from the formation of Ti 2Ni ( α phase transition), the other peak is mainly due to the formation of Zr 2Cu ( β phase transition). At the beginning of the crystallization, the activation energy of the α phase is smaller, and it increases with increasing crystallized fraction ( x c). When x c increases to 90%, the crystallization activation energy shows the largest value (220?kJ/mol). The crystallization activation energy of the β phase remains about 227?kJ/mol, as it’s crystallized fraction is below 60%, and then it increases with increasing crystallized fraction, and shows the largest activation energy of 257?kJ/mol, as the x c is 65%.
基金supported by the Key Basic and Applied Research Program of Guangdong Province,China(2019B030302010)the National Natural Science Foundation of China(51871157,51971150 and 51775351)+2 种基金the Science and Technology Innovation Commission Shenzhen(JCYJ20170412111216258)the National Key Research and Development Program of China(2018YFA0703605)Shenzhen Basic Research Project(JCYJ20190808152409578).
文摘Glass-forming ability is a long-standing concern in the field of metallic glasses(MGs),which greatly limits their maximum casting size and extensive applications.In this work,we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives.MGs with various compositions are welded together under a 20,000-Hz highfrequency ultrasonic vibration without losing their amorphous nature.The ultrasonic technology offers the advantages of rapid bonding(<1 s)at low temperature(near room temperature)and low stress(<1 MPa).According to the phenomenon observed in the experiment,the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer,and the ultrasonic vibration accelerates the atomic-diffusion process.Finally,stable bonding of the MG interface is realized.This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.
基金supported by the National Natural Science Foundation of China (11974395,11674369, and 11925408)the Strategic Priority Research Program of Chinese Academy of Sciences (CAS XDB33000000)+2 种基金the Center for Materials Genomesupport from the National Key Research and Development Program of China (2016YFA0300600, 2016YFA0302400, and 2018YFA0305700)the K. C. Wong Education Foundation (GJTD-2018-01)。
文摘Based on irreducible representations(or symmetry eigenvalues) and compatibility relations(CR), a material can be predicted to be a topological/trivial insulator(satisfying CR) or a topological semimetal(violating CR). However, Weyl semimetals(WSMs) usually go beyond this symmetry-based strategy. In other words, Weyl nodes could emerge in a material, no matter if its occupied bands satisfy CR, or if the symmetry indicators are zero. In this work, we propose a new topological invariant v for the systems with S4 symmetry(i.e., the improper rotation S_(4)(≡IC_(4z)) is a proper fourfold rotation(C_(4z)) followed by inversion(I)), which can be used to diagnose the WSM phase. Moreover, v can be easily computed through the onedimensional Wilson-loop technique. By applying this method to the high-throughput screening in our first-principles calculations, we predict a lot of WSMs in both nonmagnetic and magnetic compounds.Various interesting properties(e.g., magnetic frustration effects, superconductivity and spin-glass order,etc.) are found in predicted WSMs, which provide realistic platforms for future experimental study of the interplay between Weyl fermions and other exotic states.
