On the secondary recrystallisation of Ma754

The origin of the strong 〈100〉 fibre texture observed after the secondary recrystallisation at 1300°C of ODS MA754 has been investigated by FEG-SEM EBSD. The as-received grain size is bimodal, with occasional grains (embryos) that possess a six-fold size advantage over the "matrix" grains. The origin of the strong 〈100〉 fibre texture exhibited by the extruded alloy is shown to be unlikely to arise from a mobility advantage derived from its orientation relationship with the matrix. The matrix is weakly textured and calculations of average misorientation reveal that the 〈100〉 migrating boundaries have no special attributes. A mean field analysis has shown that secondary recrystallisation can take place in the presence of a stable dispersion once a grain with a critical size advantage is established. Under these circumstances, abnormal grains would not require an energy or mobility advantage, since they would not be competing with normal grain growth (which remains pinned). The origin of the strong texture originates from the triggering event, which is envisaged as a process of solute breakaway facilitated by the reduction in segregation with temperature. The existence of local mesotextures around successful 〈100〉 grains is postulated. The theory can account for some of the observed transformation characteristics such as the orientation dependence of the triggering event, and is supported by the observation that higher annealing temperatures allow grains to grow which have orientations other than 〈100〉. © 1998 Acta Metallurgica Inc