INTERACTION OF DISLOCATIONS WITH GRAIN-BOUNDARIES IN NI3AL

The interaction between slip dislocations and grain boundaries in hypo-stoichiometric Ni3Al, with and without boron, has been investigated by using the in situ TEM deformation technique. In both alloys, the slip dislocations were incorporated into the grain boundaries and remained at the point of entry. The difference between the alloys was in the dominant response mode of the grain boundary to the stress concentration associated with a dislocation pileup. In the boron-free material. the stress was relieved primarily by the nucleation and propagation of a crack along the grain boundary. In contrast, in the boron-doped material, relief occurred by the emission of dislocations from the grain boundary. These results are consistent with boron increasing the cohesive energy of the grain boundary. The slip system activated at grain boundaries in the ductile ordered alloy was shown to satisfy the same slip transfer criteria that operate in f.c.c. disordered alloys.