Features of the microhardness near random and special type of boundaries in a Ni3Al intermetallic compound

Various types of the grain boundaries were identified in intermetallic compound Ni3Al polycrystals. Deviations from the stoichiometric composition were determined, and microhardness was measured inside the grains and at grain boundaries. Microhardness near special boundaries is smaller than near random boundaries and comparable with that of the bulk of grains. The energies of the random and special boundaries were estimated. It was found that the chemical compositions both near the random boundaries and in the bulk of grains deviated from the stoichiometric composition less than 0.5 at.%, and this effect was not responsible for the increased microhardness near such boundaries. The deviation from the stoichiometric composition near the special boundaries is substantially higher, reaching 2 at.%, but this does not increase microhardness in these regions. At such a level of concentration fluctuations, the microhardness near grain boundaries is effected by their energy and, correspondingly by their resistance to the propagation of plastic shear from grain to grain.