Observations of roughening/de-faceting phase transitions in grain boundaries

Abstract

Sharply faceted σ3 asymmetric tilt boundaries in Al and Au and σ11 asymmetric tilt boundaries in Al were prepared at room temperature. Each boundary contained sets of two different facets and therefore possessed a two-phase structure. These boundaries were then observed continuously by hot stage electron microscopy as they were heated to elevated temperatures and then cooled back to room temperature. Grain boundary roughening/de-faceting phase transitions were observed in which the two-phase faceted structures were replaced by roughened and delocalized single-phase interfaces which were either relatively flat or smoothly curved. Furthermore, the transition was shown to be reversible, since the reverse of this process occurred during subsequent cooling, and sharply faceted boundaries were recovered at room temperature.