The use of precipitate hardened alloys at high temperatures is often limited by the thermal stability of the precipitates. To improve the understanding of precipitate dissolution after a rapid increase of temperature, we used computer simulation to study a binary A-5 at. % B model alloy. The system consisted of A and B atoms on a quadratic lattice with nearest-neighbor attractive interactions between like atoms. The dynamics was provided by a single vacancy moving across the lattice by exchanges with neighboring atoms. The evolution of the precipitates was studied as a function of time at various temperatures Ta, starting from a given initial configuration, which was prepared by "annealing" a random mixture of A and B atoms at a low temperature inside the miscibility gap of the alloy. Depending on the new temperature Ta, different processes were observed. For Ta inside the miscibility gap, the precipitates stayed compact and dissolved partially at first, but afterwards their average size increased again by a coarsening process. For Ta outside the miscibility gap, but below the critical temperature Tc, the precipitates stayed compact and dissolved completely by evaporation of atoms from their surfaces. Above Tc, they decomposed rapidly into many smaller particles in a process that resembles an explosion. A theoretical description of these various processes, based on a phase field model, is presented.
|Number of pages||7|
|Journal||Physical Review B: Condensed Matter and Materials Physics|
|Publication status||Published - 1 May 1997|