Sequences of precipitate nucleation

摘要: Solid-solid nucleation theory, as recently extended to faceted nuclei, is applied several problems in understanding experimentally observed sequences of precipitate involving transtion phases during isothermal ageing. Transition precipitates form due a low interfacial energy resulting from greater structural similarity the matrix than equilibrium phase or succeeding transition and spite usually smaller driving force, ¦ΔG v ¦, for any these competing phases. formed after first one are predicted nucleate preferentially at interphase boundaries their predecessors, also on basis energy, rather ΔG considerations. Most examples precipitation cited literature agreement with this prediction; few exceptions found noted discussed. The preference nucleating high-energy grain dislocations other lower sites explained following basis. reduce net free needed either so much that higher ¦ becomes dominant. At sites, reduction ΔG *, activation nucleation, provided makes dominant factor causing such more rapidly.