Grain boundary order-disorder transitions

The conditions for grain boundary (GB) structural transitions are determined from a diffuse interface model that incorporates structural disorder and crystallographic orientation. A graphical construction and numerical calculations illustrate the existence of a first-order GB order-disorder transition below the bulk melting point. When thermodynamic conditions permit their existence, disordered GB structures tend to be stable at higher temperatures and are perfectly wet by liquid at the melting point, while ordered grain boundaries are meta-stable against preferential melting. We calculate GB phase diagrams which are analogous to those for liquid-vapor phase transitions.