A First-principles Study On Point Defective Structures Of B2 Type Y-based Intermetallic Compound And Electron Structures Of Ni/Ni₃Al Interfaces With Re And Ru Addition

Using CASTEP code based on first-principles, the point defective constructions and its mechanics property of B2 type intermetallic compound(eg: RuAl,YAg,YCu,YIn,YRh) , the energetics and electronic structure of Ni/Ni₃Al interface with Ru or Re or Ru and Re addition have been calculated. CASTEP is a state of the art quantum mechanics based program designed specifically for solid state materials science. CASTEP employs the Density Functional Theory (DFT) plane-wave pseudopotential method which allows you to perform first-principles quantum mechanics calculations that explore the properties of crystals and surfaces in materials such as semiconductors, ceramics, metals, minerals and zeolites. Typical applications involve studies of surface chemistry, structural properties, band structure, density of states and optical properties.The B2 type intermetallic compound, for example: RuAl,YAg,YCu,YIn and YRh alloy, exhibit excellent room temperature toughness in conventionality experiment. But other B2 type intermetallic compound, for example: NiAl alloy, is not. Based on the calculation and comparison on the heat of formation and the energy of formation of several point defective structures, the type and the geometrical configuration of point defects in B2 type intermetallic compound(RuAl,YAg,YCu,YIn andYRh) are analyzed and forecasted in the first part of this paper. Results show that the major point defects in B2-RuAl intermetallic compound are vacancy defect or anti-site defect in the Ru sublattice, i.e., Ru vacancy and Al anti-site. In rich-Ru alloy it is mainly Ru anti-site defect, whereas in rich-Al alloy it is mostly Al anti-site defect. The major point defects in B2-YX (X=Cu, Rh, Ag, In) intermetallic compound are the vacancy defect in the X sublattice or the anti-site defect in the Y sublattice, i.e., X vacancy defect in rich-Y intermetallic compound and X anti-site defect in rich-X intermetallic compound. In addition, the comparison of Cauchy pressre parameter (C12-C44) and the G/B0 values of ideal B2-YX (X= Cu, Rh, Ag, In),NiAl and RuAl crystals with their point defective structures reveals: (1)decreasing degree of C12-C44 caused by point defect in RuAl is lower than that in NiAl, which is responsible for that RuAl metallic compound with point defects has a better ductility than NiAl metallic compound with point defects at room temperature; (2) point defects are beneficial for improving the ductility of B2-YX intermetallic compound. Which maybe is responsible for the outstanding ductility of B2-YX (X= Cu, Rh, Ag, In) intermetallic compound at room temperature compared with ideal B2-YX crystals and the B2-NiAl multicrystal.The energetics and electronic structure of Ni/Ni₃Al interface with Re or Ru addition have been calculated based on first principles plane-wave pseudopotential method in the second part of this paper. The calculation of Griffith rupture work W demonstrated: (1) either the substitution of Re atom for Ni atom inγ-Ni block are profitable to improve the rupture strength of the Ni/Ni₃Al interface; (2)either the substitution of Ru atom for Ni atom or Al atom in Ni/Ni₃Al interface are profitable to improve the rupture strength of the interface too, And the best is the substitution of Ru for Al atom at the coherent Ni/Ni₃Al interfacial layer among these substitutions. For the multiple addition of Re and Ru, a obvious strengthening effect on the Ni/Ni₃Al interface compared with that of the Re or Ru addition can be seen when Re and Ru atoms occupy respectively at Ni and Al sites at (001) atomic layers adjacent to the coherent (002) interfacial atomic layer. Whereas, when Ru atom locates at Al site inγ′-Ni₃Al block and far away from the coherent (002) interfacial layer, it is found the multiple addition of Re and Ru does not further elevate the rupture strengths of Ni/Ni₃Al interface but makes them decrease to a lower value than the Ni/Ni₃Al interface with Ru addition. The analysis of electron densities of states (DOS) and the distributions of valence electron densities of Ni/Ni₃Al interface before and after alloying reveals that the alloying effect of Re and Ru on the rupture strength ofγ-Ni/γ′-Ni₃Al interface is attributed to the change of the interlayer bonding in the interfacial region induced by the stronger electronic interactions within first nearest neighbor (FNN) Re-Ni and Ru-Ni atoms compared with FNN Ni-Ni and Ni-Al.