THEORY OF PHASE TRANSITIONS AT INTERNAL INTERFACES
Le Journal de Physique Colloques
A variety of phase transitions are possible at internal interfaces. I will systematically describe from a pedagogical point of view the various classes of phase transitions which are possible. Experiments which have been performed will be mentioned at the appropriate places. Theories which predict these phase transitions and which explain the behavior associated with the transitions are emphasized. Possibilities for phase diagrams are suggested. Wetting and melting of internal interfaces will
... l interfaces will also be discussed. I. Background. A decade ago the possibility of phase transitions occuring at internal interfaces would have been discounted by many researchers. For those who would have agreed with this possibility, many would not have been convinced that the evidence was strong enough to give conclusive evidence for such transitions. Today, the evidence is conclusive. Theorists and experimentalists alike are predicting and exploring a variety of transitions in grain boundaries. (The evidence for other solid-solid interfaces, such as interphase interfaces, antiphase boundaries, and stacking faults, is not yet as convincing.) People are beginning to consider how to take advantage of phase transitions which occur in internal interfaces by the appropriate processing of materials to produce the desired mfErostructura1 properies. In this article the many types of phase transitions which are possible in internal (i.e., solidsolid) interfaces are described. I hope to provide some general principles on how to decide whai is or is not a phase transition and on what the possible phase diagrams might be. A classification of most (if not all) of the work done on these transitions is provided. I intend to provide a fairly complete bibliography which will reference articles which have modeled such phase transitions and also observed them in both computer and "real" experiments. The thermodynamics of such phase transitions, which has been addressed in the past [1,2], will be discussed here where clarification is helpful. I am neglecting from consideration interface phase transitions associated with magnetism or other similar effects. For up-to-date collections of recent work in grain boundaries and other internal interfaces, I recommend one book , one review article , and two conference proceedings [5, 6] . Other recent review articles which discuss grain-boundary phase transitions may also be found (71. Article published online by EDP Sciences and available at http://dx.