Composition design of high yield strength points in single-phase Co-Cr-Fe-Ni-Mo multi-principal element alloys system based on electronegativity,thermodynamic calculations,and machine learning

A method which combines electronegativity difference,CALculation of PHAse Diagrams(CALPHAD) and machine learning has been proposed to efficiently screen the high yield strength regions in Co-Cr-Fe-Ni-Mo multi-component phase diagram.First,the single-phase region at a certain annealing temperature is obtained by combining CALPHAD method and machine learning,to avoid the formation of brittle phases.Then high yield strength points in the single-phase region are selected by electronegativity difference.The yield strength and plastic deformation behavior of the designed Co_(14)Cr_(30)Ni_(50)Mo_(6)alloy are measured to evaluate the proposed method.The validation experiments indicate this method is effective to predict high yield strength points in the whole compositional space.Meanwhile,the interactions between the high density of shear bands and dislocations contribute to the high ductility and good work hardening ability of Co_(14)Cr_(30)Ni_(50)Mo_(6)alloy.The method is helpful and instructive to property-oriented compositional design for multi-principal element alloys.

Intrinsically asymmetric atomic character regulates piezoelectricity in two-dimensional materials

Decreasing of layer thickness causes the decrease of polarization until it disappears due to the existence of depolarization field.Therefore,the search for strong piezoelectric materials is highly desirable for multifunctional ultra-thin piezoelectric devices.Herein,we propose a common strategy for achieving strong piezoelectric materials through the electronic asymmetry induced by the intrinsically asymmetric atomic character of different chalcogen atoms.Accordingly,in the tetrahedral lattice structures,for example,M4X3Y3(M=Pd/Ni,X/Y=S,Se or Te,X≠Y)monolayers are proved to display excellent out-of-plane piezoelectricity.Ni4Se3Te3 possesses the largest piezoelectric coefficient d33 of 61.57 pm/V,which is much larger than that of most 2D materials.Enhancing the electronic asymmetry further increases the out-of-plane piezoelectricity of Janus M4X3Y3 materials.Correspondingly,the out-of-plane piezoelectricity is positively correlated with the ratio of electronegativity difference(Red)and the electric dipole moment(P).This work provides alternative materials for energy harvesting nano-devices or self-energized wearable devices,and supplies a valuable guideline for predicting 2D materials with strong out-of-plane piezoelectricity.

Structural evolution and superconductivity tuned by valence electron concentration in the Nb-Mo-Re-Ru-Rh high-entropy alloys

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.

Morphological Evolution of Fe-Rich Phases in the AlSi_9Cu_3Mg_(0.19)(Fe)Alloy with the Addition of Minor Mn and Cr

The morphological evolution of Fe-rich phases in the Alalloy has been investigated with various contents of Fe,Mn,and Cr.The results show that coarse Chinese script Fe-rich phases appear in the alloy with 0.6 wt%Fe combined with trace Mn,while the blocky Fe-rich phases appear combined with trace Cr.Under the coexistence of trace Mn and Cr,a large number of fine Chinese script Fe-rich phases could be visible in the low iron-bearing AlSi_9Cu_3-alloy（0.60 wt%）.At high Fe level（1.30 wt%）,numerous Fe-rich phases with hexagonal morphologies are observed with the trace Cr,while fish-bone and pentagonal morphologies of Fe-rich phases could be simultaneously observed with the addition of both Mn and Cr.The results reveal that the trace Mn and Cr promote the morphological evolution of Fe-rich phases.The morphology evolution mechanism of Fe-rich phases has been discussed by using the atom radius and electronegativity differences of Fe,Mn,and Cr.