NUCLEATION OF RECRYSTALLIZATION IN BORON-DOPED NI3AL

The microstructural changes and the early stages of recrystallization were investigated during annealing of cold rolled boron doped Ni3Al. H ot stage TEM experiments allowed the in-situ observation of the micros tructure development during annealing. Samples from bulk annealed mate rial were examined for comparison. No cell formation look place in the grain interior during deformation, but subgrains appeared at the high angle grain boundaries of the deformed matrix during annealing, often followed by grain boundary bulging. Nucleation occurred preferentiall y al prior grain boundaries for low to intermediate degrees of rolling , but at shear bands after large deformation. Twinning and the formati on of twin chains were observed even at incipient stages of recrystall ization. It is proposed to attribute the accelerated recovery at grain boundaries to an enhanced vacancy supply in the vicinity of the grain boundaries. A simple dislocation model is introduced to account for s ubgrain and bulge formation at grain boundaries. (C) 1998 Acta Metallu rgica Inc.