National Nuclear Center of Republic of Kazakhstan, Kurchatov, Kazakhstan:

M. K. Skakov, Head of Institute of Nuclear Energy
B. K. Rakhadilov, Senior Researcher of Institute of Nuclear Energy

Shakarim State University of Semey, Semey, Kazakhstan:

Zh. B. Sagdoldina, PhD, e-mail: sagdoldina@mail.ru

O. A. Stepanova, Head of a Chair of Engineering Physics and Thermal Energetics

This article shows the results of studies of intermetallic compounds formation on the surface of TiAl (γ) alloy after Al coating and subsequent vacuum annealing at the temperatures of 600 and 700 ^оC for 2 hours. The diffusion surface enrichment of TiAl (γ) aluminum is used to improve the hightemperature oxidation resistance of the alloy. By magnetron sputtering, the surface of the alloy Ti – 42Al – 2.5Cr – 1Nb – 0.7Si – 0.5B (% (at.)) was coated with Al (500 nm thickness). Phase composition and surface morphology of the alloy were studied after vacuum annealing. Processes occurring in the vacuum annealing cause the changes in the coating morphology with formation of “bumps”, which can serve as the preferred centers of formation of new Ti – Al compounds. Based on the analysis of the impact of excess Al atoms per lattice TiAl (γ), it is shown that the diffusion process takes place without the formation of structural vacancies, and the dominant structural defects are antisite defects (Al → Ti). According to this mechanism, the displacement of the aluminum atoms in direction to the crystal surface is accompanied by relaxation of the elastic energy associated with the distortion of the crystal lattice, which results in a change in the surface morphology of the sample after vacuum annealing. There was conducted the X-ray phase analysis of the surface layers of samples in parallel X-ray beam geometry by a sliding irradiation of the surface samples of X-ray beam at a small angle of incidence. The results of phase analysis of the surface of a thin layer showed formation of new Al3Ti and Al₂Ti intermetallic compounds after annealing at 600 ^оC. Increasing of vacuum annealing temperature to 700 ^оC does not change the phase composition of the surface layer. However intensity of diffraction reflections increased regarding Al₃Ti, TiAl and Al₂Ti reflexes. Thus, the application of thin coatings on Al alloy surface TiAl(γ) and vacuum annealing can modify the surface properties of the structural phase of the alloy to form the new Ti – Al intermetallic compounds.

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