This paper reports that one of the critical issues in developing an understanding of the response of Ni{sub 3}Al to stress is the interaction between dislocations and grain boundaries. Even in simple metals this issue is complex, depending as it does on the nature and orientation of the grain boundary and the character of the interacting dislocations. In the case of intermetallic alloys, the issue is even more complex, as the additional factors of grain boundary chemistry, local order, etc. play an important role. This si clearly illustrated in the specific case of Ni{sub 3}Al which exhibits brittle intergranular fracture at low temperatures, except for hypo-stoichiometric alloys containing small amounts of Boron. The B-doped alloy exhibits extensive plastic deformation before undergoing ductile rupture. The effect of B is clearly on the response of grain boundaries to the stresses caused by slip dislocations as both ductile and brittle alloys show extensive slip within the grains prior to fracture. Two mechanism have been proposed to account for this effect of B on the fracture process. In one, it is postulated that B segregation to the grain boundaries increases the cohesive energy of the grain boundaries to the extent that stress concentrations atmore » the boundaries are relieved by initiation of slip rather than fracture. This is consistent with the thermodynamic treatment of fracture as it has been observed that B does segregate more strongly to grain boundaries than to external surfaces.« less