Coarsening of second phase in a two-phase Zr-2.5Nb: On the role of phase boundaries

Deformed two-phase Zr-2.5Nb was subjected to 700 degrees C annealing and associated coarsening. After primary recrystallization, the second-phase body-centered cubic beta was well dispersed on the grain boundaries of hexagonal alpha matrix. Prolonged annealing led to the presence of the beta, mainly at the alpha tri-junctions. The two-phase coarsening was associated with clear trends of widening in the second-phase size distribution and changes in phase boundary nature. The former is contrary to what is expected. Changes in phase boundary nature were through increased concentration of 45 degrees[0 0 1] phase boundaries-good-fit interfaces, present in larger beta particles, which were estimated to have higher three-dimensional lattice coincidence and hence lower energy. Simple analytical modeling, assuming dissolution-controlled particle coarsening and a lower interfacial energy of the phase interface with the 45 degrees[0 0 1], was shown to explain these experimental observations. (C) 2009 Acta Materialia Inc