Microhardness near boundaries of various types in an intermetallic compound Ni3Al

Grain boundaries of various types were identified in Ni3Al intermetallic compound crystals. Deviations from the stoichiometric composition were determined, and microhardness was measured in the bulk of grains and at grain boundaries. Microhardness near special boundaries is smaller than near general (randomly oriented) boundaries and comparable with microhardness in the bulk of grains. The energies of the general and special boundaries were estimated. It was found that the chemical compositions both near the general 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 determined by their energy and, correspondingly, by their resistance to the propagation of plastic shear from grain to grain, while the microhardness of the general boundaries is also deter-mined by impurity segregates.