First-principles Study Of Effects Of The Non-metallic Elements On The Mechanical Properties In Ni And Ni₃Al

Characterized by excellent mechanical properties,Ni,Ni₃Al,and Ni-based superalloys have been used widely to produce structural materials.Alloying elements have critical effects on the mechanical properties of materials.The research systemically analyzed the influences of main-group non-metallic elements X?X=H,B,C,N,O,Si,P,S,As,Se,and Te?on the mechanical properties of Ni and Ni₃Al including structural and elastic properties as well as ideal strength based on density functional theory and using the first-principles method.In addition,the electronic mechanism behind the influences of main-group non-metallic elements was also investigated.The research results provide significant scientific reference for the alloy design.The equilibrium calculation using the first-principles method found that a system was in cubic and tetragonal structures when non-metallic elements occupied different interstitial sites of Ni₃Al.While the interstitial phases of Ni all showed the cubic structure.Meanwhile,the atomic radius of non-metallic elements deeply influenced the expansion of interstitial phases.The calculation of enthalpy of formation and binding energy of the system revealed that the addition of elements B,C,and N were able to effectively improve the phase stability of Ni and Ni₃Al.Moreover,most non-metallic elements tended to occupy the Ni-rich interstices in Ni₃Al.The addition of these non-metallic elements can always reduce the elastic modulus while improve the ductility of Ni,while it showed diversified influences on the elastic modulus of Ni₃Al.Further research indicated that the elastic parameters of the system were correlated with the structural parameters.The addition of non-metallic elements reduced the anisotropy of Ni and Ni₃Al.Among the non-metallic elements,the addition of As decreased the anisotropy of Ni and Ni₃Al to the lowest level.The analysis of differential charge density revealed that the influences of the non-metallic elements on the elastic properties of Ni and Ni₃Al were related to the covalent-like bonds between the non-metallic atoms and the nearest-neighbor Ni atoms.The uniaxial tensile tests based on first-principles were conducted to symmetrically study the influences of main-group non-metallic elements on the ideal tensile strength?_IT and critical strain?_C of Ni and Ni₃Al.The results showed that the addition of non-metallic elements all reduced the?_IT and?_C of Ni and Ni₃Al in the[001]and[111]directions.Ni?X?and Ni₃Al?X?presented close and concentrated?_IT and?_C in the[001]direction,while they were fractured at?_C in the[111]direction.In comparison,the influences of non-metallic elements on?_IT and?_C of Ni and Ni₃Al in the[110]direction were diversified.By analyzing the evolution of the lattice in the tensile process along the[110]direction,we can found that the addition of non-metallic elements was able to effectively reduce the change rates of lattice parameters of Ni and Ni₃Al in vertical tensile direction.That is,it improved the deformation resistance of Ni and Ni₃Al.Moreover,the larger the strain amplitude and the periodic number of X,the more significant the deformation resistance was.In the tensile process along the[110]direction,Ni in the FCC structure and Ni₃Al in the L1₂ structure formed unstable Ni and Ni₃Al crystal structures when the strain was 17%.As a result,the structure yielded earlier along the[110]direction than along the[001]and[111]directions,that is,the[110]direction was the weakest uniaxial tensile directions.Furthermore,the electronic mechanism of non-metallic elements for influencing the tensile strength was analyzed in detail by calculating the electronic structure.