Features of non-isothermal grain boundary diffusion in Ti3Al

A two-dimensional diffusion-kinetic model is proposed to research the effect of oxygen diffusion along grain boundaries on the oxidation dynamics of the intermetallic alloy Ti3Al. The contribution of grain boundaries is evaluated by comparing the dynamics of processes in a structure with clearly defined grains and boundaries and in a material with effective properties, where the diffusion coefficient was calculated depending on the fraction of the boundary phase. Oxygen diffusion occurs in a mixed kinetic mode typical of additively fabricated nanoscale structures. The structure with an explicit consideration of grains and boundaries in the model has its symmetry. Rectangular grains are located relative to each other similar to "brickwork" so that they form triple junctions. The material with effective properties is a continuous rectangular region, in which the fraction of the boundary phase is taken into account through the diffusion coefficient. A constant oxygen source is specified on the surface. The problem is solved numerically in dimensionless variables. An implicit difference scheme of splitting by coordinates is used to solve the diffusion equation. To solve the kinetic equations, a method similar to the explicit Euler method is used with the organization of the iterative process. The results are compared for the isothermal mode and for the conditions of linear heating with subsequent cooling. The study is carried out for the initial stage of oxidation of the nanosized intermetallic alloy Ti3Al. The contribution of grain boundaries to the oxidation dynamics is estimated in the range of the fraction of the boundary phase from 0.1 to 0.5, which changes due to the variation of the grain sizes relative to the boundary width. The results obtained are in a qualitative agreement with the literature data.