It was recalled that the mobility of grain boundaries was usually measured by using the so-called quarter-loop and Sun-Bauer methods. That is, a grain boundary was allowed to migrate and its tip position along a free surface was recorded in order to deduce the mobility. At the tip, a groove developed in order to reduce the combined surface energy. The groove was small and adjusted quickly. In both methods, the groove could be treated - at each instant - as migrating at a constant speed. This quasi-steady groove, formed via surface diffusion, was studied and it was found that the groove turned the grain boundary, by θ, away from the perpendicular to the free surface. This tilting effect was incorporated into both measurement methods by solving the migrating grain-boundary profiles for arbitrary θ. The calculated profiles agreed well with Sun-Bauer experiments where θ was 18 or 30°.

A Model of Migrating Grain-Boundary Grooves with Application to Two Mobility-Measurement Methods. D.Min, H.Wong: Acta Materialia, 2002, 50[20], 5155-69