Scanning probe microscopy study of grain boundary migration in NiAl Original Research Article

A post-mortem scanning probe microscopy (SPM) study of grain boundary migration in Ni-rich NiAl at 1400 °C is presented. The migration of grain boundaries during annealing is quantified using the SPM measurements of surface topography of the regions swept by migrating grain boundaries. It is shown that the quantitative conclusions about the dynamics of grain boundary motion can be drawn from the study of surface topography in the vicinity of both individual migrated boundaries and migrated triple junctions. In the case of individual boundaries, the curvature of the blunted root of the grain boundary groove formed at original boundary position provides the information about the beginning of migration process. In the case of triple junctions that moved along one of three boundaries forming the junction, the variable width of the grain boundary groove allows to recover the dynamics of migration process. Using the Mullins model of grain boundary grooving and its modifications we estimated that the grain boundary migration rate is 0.52 ± 0.09 μm/s. This is much higher than the average migration rate obtained by dividing the migrated distance by total annealing time. It is concluded that in the near-surface region of NiAl the grain boundaries migrate in jerky, spasmodic fashion.