Oxidation of TiAl alloy by oxygen grain boundary diffusion.

Ti–Al intermetallic alloys have a number of advantages for the manufacture of aviation and car details. The use of these alloys is limited by their oxidation at high temperatures, which is associated with structural features and the presence of micro and nanosized grains. In such materials, grain boundary diffusion of oxygen can be active, which contributes to the acceleration of oxidation upon heating. In this paper, we present a two-dimensional model for research the diffusion which is accompanied by oxidation. The structure of TiAl is specified as symmetrically alternating grains with a clear separation of boundaries and triple junctions between them. Diffusion and chemical properties of grains and boundaries are different. The problem is formulated in a two-dimensional formulation and solved numerically. The influence of changes in the composition over time on the penetration of oxygen is taken into account. For the convenience of numerical research and analysis of the results, dimensionless variables are used. To solve the diffusion equation, an implicit difference scheme of splitting in coordinates is used. The equations of chemical kinetics are solved using an algorithm similar to the implicit Euler method using an iterative procedure. The results demonstrate the influence of different variants of kinetic regimes on the concentration distribution and integral concentrations of reagents and oxides. • A two-dimensional model is used to analysis the oxidation of TiAl alloy. • Grain boundary diffusion and oxidation are modeled for isothermal conditions. • Two kinetic regimes are revealed for the case of oxides accumulation in surface layer and for the case of predominant oxidation along grain boundaries. • It is detected that concentration dependence of diffusion coefficient affects the oxidation dynamics. [ABSTRACT FROM AUTHOR]