First-Principles Calculations of Oxygen Diffusion in Ti-Al Alloys

Abstract

The projector augmented-wave method within the density functional theory is applied to investigate the oxygen diffusion in the intermetallic Ti-Al alloys. It is shown that the highest oxygen absorption energies in Ti-Al alloys correspond to the octahedral Ti-rich sites but the presence of aluminium in the nearest neighbours leads to a substantial decrease in the oxygen absorption energy in the alloys. The migration barriers for the oxygen diffusion between various interstices in the crystal lattice of the Ti-Al alloys are estimated. The preferred migration paths along a and c axes and limiting barriers of the oxygen diffusion in the alloys are determined. The dependence of the oxygen diffusion coefficient on Ti-Al alloy composition is discussed.

First-principle study of the solubility and diffusion of oxygen and boron in γ-TiAl

“…Between the two octahedral sites, for both the elements, the center of the [Ti 4 Al 2 ] octahedron is the stablest position. The oxygen preference for the Ti-rich site is in agreement with several previous works [26,27,28,29,31].…”

“…The diffusion coefficients as a function of the temperature are shown in Fig. 10 and compared to the available experimental data, for boron [50], and to the calculated values from Kulkova [31], for oxygen. A very good agreement between the calculations from this work and the literature data can be observed.…”

“…Zhao et al [30] used DFT to compute the barrier energies for the oxygen diffusion in bulk γ-TiAl and Nb-doped γ-TiAl, but they did not provide diffusion coefficients. Kulkova et al extended the investigation and provided computed values for the diffusion coefficients of oxygen in bulk γ-TiAl [31]. These authors adopted the same computation scheme previously adopted by Bakulin et al for Ti 3 Al [23]: barrier energies ∆E were obtained by DFT calculations and jump frequencies ν * were estimated as ∆E/(2md 2 ), with m being the oxygen mass and d the path length.…”

“…Moreover, the same computation methodology has been recently applied to study the hydrogen diffusion in γ-TiAl [40]. This more rigorous method is here applied to compute the diffusion coefficients of oxygen in γ-TiAl and the results are compared to the previous values from Kulkova et al [31].…”

VLIYaNIE PRIMESEY NA DIFFUZIYu KISLORODA V TiO2

“…Экспериментально на поверхности сплавов Ti 3 Al и TiAl обнаружен рост смешанных оксидных слоев [1,[4][5][6], при этом наблюдается частичное осыпание верхних слоев оксидных пленок, которые не контактируют со сплавом. Для понимания механизма окисления Ti-Al сплавов, нами было проведено изучение адсорбции кислорода на низко-индексных поверхностях [7,8], а также его диффузии как в объеме сплавов, так и с их поверхности [9][10][11]. Известно, что низкая скорость диффузии и высокие активационные энергии благоприятны для высокотемпературных структурных материалов.…”