Abstract:
The accumulation of various defects in the material structure during its exploitation poses the most important limit on its lifetime. One of the simplest and most effective methods for restoring the nominal properties of the materials is through thermal annealing. The annealing can be both homogeneous and heterogeneous, depending on the manner in which activation occurs. It is known that, under certain conditions, the heterogeneous annealing is self-sustaining and can propagate like a travelling wave, due to a nonlinear thermal-concentration feedback.
In this study numerical modelling of the heterogeneous annealing in a finite one-dimensional geometry was performed. To this end, a finite difference solver was implemented, verified and applied in our numerical experiments. The self-sustaining annealing process was initialized by adding heat to a localized region near the material surface at the initial moment. The evolution of temperature and defect distributions during the process of annealing was obtained for different initiating heat distributions and initial defect concentrations.
It was demonstrated that for large values of initiating energy, the annealing process develops as a wave, which propagates at a constant speed. For more moderate values of initiating energy, the interplay of the heterogeneous initial heat distribution and the spontaneous annealing leads to the appearance of the wave regime in the terminal part of the process. The time required for the number of defects in the material to fall below a given small fraction of their initial value is a measure of overall efficiency of the annealing process. The dependence of this time on the initial conditions and initial heating parameters was studied.
