Vacancy-induced dissolution of precipitates in out-of-equilibrium systems: A test case ofFeX(X=C,N,O) alloys

Abstract

Various out-of-equilibrium processes produce a supersaturation of vacancies in the material. When these defects show attractive binding energy with solutes, they will form stable point defect-solute clusters which will stabilize solutes in the solid solution with respect to the equilibrium case. Hence the out-of-equilibrium dynamic solubility limit increases, which can lead to the dissociation of solute precipitates. This vacancy-induced precipitate (VID) dissolution mechanism is an alternative to the well-known ballistic mixing effect (BAL) under irradiation, and it is also relevant for quenching, ball milling, and severe plastic deformation. Under irradiation, a BAL is efficient at low temperature only, whereas a VID is expected to be effective at intermediate temperatures. A quantitative and consistent prediction of the interstitial solute solubility limit increase generated by both BAL and VID mechanisms is presented starting from ab initio binding energies and migration energies of solutes and point defects, and using a low-temperature expansion of the free energy of the solid solution. These results are discussed for three alloys: FeC, FeN, and FeO, the latter being relevant to discuss the stability of oxide dispersed strengthened alloys microstructure under irradiation. We also suggest an experiment that would be able to determine steady-state vacancy supersaturations from the measure of solute partial pressures in out-of-equilibrium systems.