Ordered Alloy Of Point Defects In Modified Analytical Embedded Atom Method Simulations

Because the ideal situation-absolute zero degrees can not be achieved, the atoms of the material will deviate from their point of Brad Ludwig due to thermal fluctuations, which will produce a large number of point defects in the material. The presence of these point defects greatly affects the materials'mechanical characteristics, mechanical properties, and electromagnetic properties and so on. Therefore, studying the characteristics of defects in the material, the formation of defects as well as the interaction between them has an important practical significance.In this paper, the physical characteristics of the defects are studied through MAEAM by taking the B2-type TaW and Llo-type CuAu ordered alloys for example. The characteristics include the equilibrium lattice constant, cohesive energy, formation energy, the energy of the mono-vacancy and anti-site defect, the formation energy and binding energy of di-vacancy, as well as the migration energy and activation energy in different migration mechanisms calculated with modified analytic embedded-atom method. At last, according to the principle of energy minimization, the favorable migration mechanisms of the mono-vacancy in the alloys are discussed in detail. The results are as follows:(1) The calculated lattice constant is a of 3.2316A and the formation energy is⊿EC of-0.0950eV which is in accord with the results of a of 3.2450A and⊿EC of-0.1035eV calculated by the ab initio. Besides, CuAu ordered alloys'equilibrium lattice constant, cohesive energy, formation energy are a of 3.9640A, c of 3.6720A, Ec of 3.8673eV,⊿EC of-0.1323eV respectively which are in good agreement with the results of the first principles or experimental data a of 3.966A,c of 3.673A,Ecof 3.74eV,⊿Ecof-0.15eV. All the data above indicate that the MAEAM can describe the physical properties of these two alloys well.(2) The energy of mono-vacancy and anti-site of Ta (W) in TaW ordered alloy is VTa=3.4814eV and Taw=0.9730eV (Vw=3.7014eV and WTa=-0.6583eV) respectively. The energy of mono-vacancy and anti-site of Cu (Au) in CuAu ordered alloy is VCu=1.1795eV and CuAu=0.0587eV (VAu=1.1958eV and AuCu=0.7456eV) respectively. When the two alloys deviate from their perfect stoichiometric, the anti-defects are more available due to their lower formation energies. For di-vacancy in TaW (and CuAu) alloy, its configuration order is VTa-w,VTa-Ta,VW-W and VCu-AU,VCu-Cu,VAu-Au according to their required formation and binding energies.(3) In order to discuss the effect of the cutoff distance rc of the potentials on the vacancy migration energy and activation energy in alloys, an accurate calculation of them in two different cutoff distances are conducted by taking the next-nearest-neighbor jump (1NNNJ) for example. The result shows that the cutoff distance has little effect on the calculated results and the relative errors of different cutoff distance are lower than 10%. So we conclude that the cutoff distance is not the main factor to affect the results. And we use rc=rc2=r2e+0.75(r3e-r2e) as the cutoff of the potentials suggested by the next-nearest-neighbor model of the MAEAM.(4) In the six different migration mechanisms of the mono-vacancy in the TaW alloy, only the energy-displacement curves of 1NNNJ and 1TNNJ are symmetrical about the midpoint of the migration path. Among them, the 1NNJ has the lowest activation and migration energies, but it will introduce an anti-site defect which results in a disorder in the TaW ordered alloy. Although the energy-displacement curves of 1NNNJ and 1TNNJ can ensure the order of the TaW ordered alloy, but higher migration energy are needed, which is not conducive to the migration. Therefore, the 1NNNJ or 1TNNJ will be replaced by six successive 1NNJ constructed here. For a Ta mono-vacancy, the sequence of favorable migration mechanisms is 1NNJ, S[100]6NNCJ, B[100]6NNCJ, [110]6NNCJ, ranging from easy to difficult. Also for a W mono-vacancy, the sequence is gradually 1NNJ, S[100]6NNCJ, B[100]6NNCJ(or [110]6NNCJ).(5) In the five different migration mechanisms of the mono-vacancy in the CuAu alloy, except 1NNJ and 1NNNJ, the energy-displacement curve is not symmetrical about the midpoint of each jump. In five migration mechanisms of either a Cu or an Au mono-vacancy, the ASB migration is the most favorable and the 1NNNJ is the most difficult mechanism. So,1NNNJ will be replaced by six successive 1NNJ constructed here. For a Cu mono-vacancy, the sequence of favorable migration mechanisms is ASB,1NNJ, B[001]6NNCJ, S[001]6NNCJ, ranging from easy to difficult while for a Cu mono-vacancy the sequence is ASB, B[001]6NNCJ(or S[001]6NNCJ),1NNJ.