Recent developments concerning segregation and fracture at grain boundaries

Certain trace impurities have long been known to embrittle grain boundaries in polycrystalline metals and alloys. In recent years a large body of evidence, directly connecting impurity segregation to intergranular failure, has become available. Indeed, it was conventional wisdom for a time that all intergranular failure could be attributed to segregation of embrittling impurities, and that all segregation degrades grain boundary cohesion. There have been several interesting experimental and theoretical developments during the last 5--10 yr that run counter to this conventional wisdom, the study of which may significantly advance our understanding of the mechanism by which impurities affect grain boundary cohesion. Several examples of beneficial grain boundary segregants will be presented, and the relationship between segregation behavior and grain boundary cohesion will be discussed