First-principles Calculation Of The Effect Of Point Defects On The Mechanical Properties Of ? And ?' Phases And ?/?' Interfaces

Ni-based single crystal?NSC?superalloys are key material of turbine blade in advanced aeroengines.The strengthening mechanism of?'-Ni₃Al precipitate,?-Ni matrix and Ni/Ni₃Al interface is studied to help guide the development of a new generation of nickel-based single crystal superalloys.Thus,this paper adopts the first-principles calculation method and conducts the following research.?1?Based on the first-principle calculations,the effects of Al antisite and Ni vacancy concentration on the mechanical properties of Ni₃Al and Ni crystals were compared and compared with the empirical formula calculation results.The results show the Young's modulus of single-crystal Ni₃Al in<001>and<011>direction,and shear modulus in<011>and<111>increase with the increase of Al antisite concentration.And the Young's modulus E and the shear modulus G of the polycrystalline Ni₃Al are not substantially affected by the content of Al antisite.With the rise of the Ni vacancy concentration,the E and G of all orientations of the single-crystal Ni decline significantly,and the E and G of the polycrystalline Ni also decline.The empirical formula calculation of this result shows that the change in bulk modulus can be predicted by electron density and volume.?2?Using a first-principles calculation,the electronic structures of Ni₃Al with different point defects were calculated.The results show isolated Al antisite(Al _Ni)or Ni antisite(Ni _Al)is profitable to improve the strength of Ni₃Al,while most complex composition defects make the strength of Ni₃Al be weakened.Among which the Al _Nii is the best but the first nearest neighbor Al _Ni-Al _Ni complex defect is worse.These results help interpret that stoichiometric Ni₃Al exhibited lower yield stress below the peak temperature,but higher yield stress above the peak temperature compared to Al-rich and Ni-rich crystals.The analysis of electronic structures reveals the detrimental effect of point defect mainly originates from the distribution of charge density,for instance the spherical distribution of charge density facilitates shear deformation,resulting in a lower shear-related property.?3?A first-principles investigation on the rupture strength W₀ of?-Ni/?'-Ni₃Al interfaces with and without P-doping is conducted,and the influence of phosphorous content x on W₀ is also evaluated.The results show the advantageous and disadvantageous impact of phosphorous on rupture strengths W₀ of Ni/Ni₃Al interfaces mainly depends on their inter-phase fracture sites related to doping types.With the increase of P content x,the Griffith rupture work W of Ni/Ni₃Al interfaces firstly decreases and then increases,and a minimum appears at x=0.018 wt.%.This good agreement with the x dependence of ultimate tensile strengths of IN718superalloys indicates the W₀ can be applied to characterize the tensile strength of Ni-based superalloys to some extent.The analysis of electronic structures reveal the detrimental effect of P-doping mainly originates from the weakened electronic affinity between interfacial atoms,but an elevated local elastic strain energy caused by the substitution of P for Ni cannot be neglected.As a result,the P-doping at octahedral interstices in?'-phases has a higher W than the substitution of P for Ni in?-phases.