AbstractThis paper reports measurements of large sample populations of grain boundary geometries–both grain misorientations and boundary plane orientations–in annealed nickel. Two heat treatment schedules are represented: one in which a specimen is heated at 1000°C for 1 h (the‘fast’specimen) and another which combines this treatment with a slow heating and cooling cycle (the‘slow’specimen). There was a marked difference between the proportions of‘geometrically special’boundaries in the two data sets, with the slow set containing almost double the proportion of coincident site lattice boundaries (CSLs) observed for the fast set. Furthermore, of the CSLs in the slow set, half were tilts or twists (mostly asymmetrical tilts), compared with less than a quarter of the CSLs in the fast set. The interpretation of these data is that kinetic factors have a strong influence on the evolution of populations of‘special’boundaries.MST/1431