Transmission electron microscopy, optical microscopy, and electron microprobe analysis were used to study the microstructure, local deviations from the stoichiometric composition, parameters of grain structure, the energy of various grain boundaries, and mechanical properties depending on the boron concentration in Ni3Al with 24at%Al, which was produced by the self-propagating high-temperature synthesis. It was found that 0.5at%B was the most optimum concentration to produce favorable mechanical properties of this alloy, namely, the yield strength, ultimate strength, and plasticity. All the grains were mono-domains with randomly distributed dislocations. At the grain boundaries and dislocations, a nanocrystalline phase Ni3B was formed. Distributions of the local deviations from the stoichiometric composition inside the grains and near the boundaries of different types were obtained. Inside the grains and near the boundaries of special type, the most probable nickel contents were higher than the stoichiometric concentrations; near the boundaries of random (general) type, they were lower than the stoichiometric concentrations. An increase in the average energy of special boundaries indicates a rise in the energies of stacking faults and antiphase boundaries. Upon plastic deformation, the intragranular strengthening (unlike unalloyed Ni3Al) was additionally caused by the presence of solid solution of boron in the crystal lattice and nanocrystalline Ni3B at dislocations and grain boundaries. The deviation from stoichiometry near grain boundaries must cause, on the one hand, a deceleration of shear at near-boundary regions and, on the other hand, a decrease in the order parameter of the crystal lattice in the vicinity of these boundaries and an increase in their imperfection, which was a probable factor responsible for a decrease in the resistance of grain boundaries to plastic shear.

Effect of Nanocrystalline Nickel Boride on the Microstructure and Mechanical Properties of Intermetallic Compound Ni3Al Alloyed with Boron. Perevalova, O.B., Ovcharenko, V.E., Igonin, N.G.: Fizika Metallov i Metallovedenie, 2004, 97[4], 103-10