Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties.However for some of these appli...Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties.However for some of these applications,high plastic deformability is required to achieve desired component shapes and configurations;unfortunately,Mg and its alloys have low formability.Scientifically,the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems.But basically,the HCP crystal structure coupled with low stacking fault energies(SFE)are largely linked to the poor ductility exhibited by Mg alloys.These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys.Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability–mediated engineering use have been reported and still ongoing.This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour,specifically,plasticity characteristics.It also concisely presents various processing routes(Alloying,Traditional Forming and Severe Plastic Deformation(SPD))which have been explored to enhance plastic deformability in Mg and its alloys.Grain refinement and homogenising of phases,reducing CRSS between slip modes,twinning suppression to activate non-basal slip,and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes.While identifying the limitations of these strategies,further areas to be explored for enhancing plasticity of Mg alloys are highlighted.展开更多
A hybrid first-principles/Monte Carlo simulation is combined with experiments to study the structure and elastic properties of CoCrNi_x(x=1-0.5)alloys.The experimental X-ray diffraction patterns show that the structur...A hybrid first-principles/Monte Carlo simulation is combined with experiments to study the structure and elastic properties of CoCrNi_x(x=1-0.5)alloys.The experimental X-ray diffraction patterns show that the structures have changed from the single-phase face-centered cubic(FCC)structure at x=1-0.8 to the coexistence of FCC and the hexagonal close-packed structures at x=0.7-0.5,which is further confirmed by calculations on mixing energies.The elastic moduli by calculation are basically in agreement with experiments.Room-temperature tension shows that the six alloys have a certain plasticity,the strength and plasticity of the alloys have a linear decrease with the decrease in Ni contents,and the plasticity of the alloys drops from 84 to 23%.Furthermore,first-principles density function theory calculations were employed to reveal the electronic and magnetic structures of alloys.The electron density of states for all alloys is asymmetrical,which illustrates that the alloys are ferromagnetism.It is found that Cr atoms can suppress the ferromagnetism of alloys,since Cr atoms have both positive and negative magnetic moments in all alloys.展开更多
The crystal structure and physical properties of Nb_(25)Mo_(5+x)Re_(35)Ru_(25-x)Rh_(10)(0≤x≤10)and Nb_(5)Mo_(35-y)Re_(15+y)Ru_(35)Rh_(10)(0≤y≤15)high-entropy alloys(HEAs)have been studied by X-ray diffraction,elec...The crystal structure and physical properties of Nb_(25)Mo_(5+x)Re_(35)Ru_(25-x)Rh_(10)(0≤x≤10)and Nb_(5)Mo_(35-y)Re_(15+y)Ru_(35)Rh_(10)(0≤y≤15)high-entropy alloys(HEAs)have been studied by X-ray diffraction,electrical resistivity,magnetic susceptibility,and specific heat measurements.The results show that the former HEAs with valence electron concentration(VEC)values of 6.7-6.9 crystallize in a noncentrosymmetric cubicα-Mn structure,while the latter ones with VEC values of 7.1-7.25 adopt a centrosymmetric hexagonal close-packed(hcp)structure.Despite different structures,both series of HEAs are found to be bulk superconductors with a full energy gap,and the superconducting transition temperature Tc tends to decrease with the increase of VEC.Nevertheless,the Tc values of the hcp-type HEAs are higher than those of theα-Mn-type ones,likely due to a stronger electron phonon coupling.Furthermore,we show that VEC and electronegativity difference are two key parameters to control the stability ofα-Mn and hcp-type HEAs.These results not only are helpful for the design of such HEAs,but also represent the first realization of structurally different HEA superconductors without changing the constituent elements.展开更多
文摘Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties.However for some of these applications,high plastic deformability is required to achieve desired component shapes and configurations;unfortunately,Mg and its alloys have low formability.Scientifically,the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems.But basically,the HCP crystal structure coupled with low stacking fault energies(SFE)are largely linked to the poor ductility exhibited by Mg alloys.These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys.Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability–mediated engineering use have been reported and still ongoing.This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour,specifically,plasticity characteristics.It also concisely presents various processing routes(Alloying,Traditional Forming and Severe Plastic Deformation(SPD))which have been explored to enhance plastic deformability in Mg and its alloys.Grain refinement and homogenising of phases,reducing CRSS between slip modes,twinning suppression to activate non-basal slip,and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes.While identifying the limitations of these strategies,further areas to be explored for enhancing plasticity of Mg alloys are highlighted.
基金the National Key Laboratory for Remanufacturing(No.61420050204)Transformation of Scientific and Technological Achievements Programs of Higher Education Institutions in Shanxi(2019)+1 种基金opening project of the State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology,No.KFJJ20-13 M)Hua Tian would like to acknowledge the National Natural Science Foundation of China(No.51901152)。
文摘A hybrid first-principles/Monte Carlo simulation is combined with experiments to study the structure and elastic properties of CoCrNi_x(x=1-0.5)alloys.The experimental X-ray diffraction patterns show that the structures have changed from the single-phase face-centered cubic(FCC)structure at x=1-0.8 to the coexistence of FCC and the hexagonal close-packed structures at x=0.7-0.5,which is further confirmed by calculations on mixing energies.The elastic moduli by calculation are basically in agreement with experiments.Room-temperature tension shows that the six alloys have a certain plasticity,the strength and plasticity of the alloys have a linear decrease with the decrease in Ni contents,and the plasticity of the alloys drops from 84 to 23%.Furthermore,first-principles density function theory calculations were employed to reveal the electronic and magnetic structures of alloys.The electron density of states for all alloys is asymmetrical,which illustrates that the alloys are ferromagnetism.It is found that Cr atoms can suppress the ferromagnetism of alloys,since Cr atoms have both positive and negative magnetic moments in all alloys.
基金financial support by the foundation of Westlake Universitysupported by the National Key Research Development Program of China(No.2017YFA0303002)。
文摘The crystal structure and physical properties of Nb_(25)Mo_(5+x)Re_(35)Ru_(25-x)Rh_(10)(0≤x≤10)and Nb_(5)Mo_(35-y)Re_(15+y)Ru_(35)Rh_(10)(0≤y≤15)high-entropy alloys(HEAs)have been studied by X-ray diffraction,electrical resistivity,magnetic susceptibility,and specific heat measurements.The results show that the former HEAs with valence electron concentration(VEC)values of 6.7-6.9 crystallize in a noncentrosymmetric cubicα-Mn structure,while the latter ones with VEC values of 7.1-7.25 adopt a centrosymmetric hexagonal close-packed(hcp)structure.Despite different structures,both series of HEAs are found to be bulk superconductors with a full energy gap,and the superconducting transition temperature Tc tends to decrease with the increase of VEC.Nevertheless,the Tc values of the hcp-type HEAs are higher than those of theα-Mn-type ones,likely due to a stronger electron phonon coupling.Furthermore,we show that VEC and electronegativity difference are two key parameters to control the stability ofα-Mn and hcp-type HEAs.These results not only are helpful for the design of such HEAs,but also represent the first realization of structurally different HEA superconductors without changing the constituent elements.
