Adsorption of oxygen on low-index surfaces of the TiAl 3 alloy
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Adsorption of Oxygen on Low-Index Surfaces of the TiAl3 Alloy A. M. Latysheva, A. V. Bakulina,b, S. E. Kulkovaa,b*, Q. M. Huc, and R. Yangc a
National Research Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia b Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences, Akademicheskii pr. 2/4, Tomsk, 634055 Russia c Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016 China *e-mail: [email protected] Received May 2, 2016
Abstract—Method of the projector augmented waves in the plane-wave basis within the generalized-gradient approximation for the exchange-correlation functional has been used to study oxygen adsorption on (001), (100), and (110) low-index surfaces of the TiAl3 alloy. It has been established that the sites that are most energetically preferred for the adsorption of oxygen are hollow (H) positions on the (001) surface and bridge (B) positions on the (110) and (100) surfaces. Structural and electronic factors that define their energy preference have been discussed. Changes in the atomic and electronic structure of subsurface layers that occur as the oxygen concentration increases to three monolayers have been analyzed. It has been shown that the formation of chemical bonds of oxygen with both components of the alloy leads to the appearance of states that are splitoff from the bottoms of their valence bands, which is accompanied by the formation of a forbidden gap at the Fermi level and by a weakening of the Ti–Al metallic bonds in the alloy. On the Al-terminated (001) and (110) surfaces, the oxidation of aluminum dominates over that of titanium. On the whole, the binding energy of oxygen on the low-index surfaces with a mixed termination is higher than that at the aluminum-terminated surface. The calculation of the diffusion of oxygen in the TiAl3 alloy has shown that the lowest barriers correspond to the diffusion between tetrahedral positions in the (001) plane; the diffusion of oxygen in the [001] direction occurs through octahedral and tetrahedral positions. An increase in the concentration of aluminum in the alloy favors a reduction in the height of the energy barriers as compared to the corresponding barriers in the γ-TiAl alloy. DOI: 10.1134/S1063776116110133
1. INTRODUCTION Among the large number of known intermetallic alloys, the greatest attention of both experimenters and theorists is paid to the alloys based on titanium and aluminum. The titanium aluminides are considered as promising structural materials for the hightemperature applications in the modern branches of industry, such as aerospace, automobile, ship building, etc. These materials possess a whole complex of good mechanical properties, such as low density, high melting point, plasticity, high strength, and heat resistance [1, 2]. The high specific strength and elasticity modulus of Ti–Al compounds as compared to the nickel superalloys make the titanium aluminides very promising
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