Correlation between grain boundary energy and geometry in Ni-rich NiAl

The relative energies of 43 different large angle grain boundaries in Ni-rich NiAl have been determined with the aid of scanning probe microscopy using the thermal grooving method at 1400 °C. Simultaneously, the geometrical degrees of freedom of the same grain boundaries have been characterized by a combination of electron back-scattering diffraction and serial sectioning techniques. The determined values of the ratio of the grain boundary to surface energy are scattered over a wide range of 0.2-1.1. It is found that twist grain boundaries exhibit higher energies than their tilt counterparts. Moreover, mixed grain boundaries with approximately equal amount of tilt and twist components do not exhibit high energies. A strong dependence of the energy of a large angle grain boundary with fixed misorientational degrees of freedom on its plane inclination has been demonstrated. The energies of several selected grain boundaries and free surfaces in NiAl have been calculated by employing an embedded-atom method (EAM) interatomic potential specially developed for NiAl. The range of possible relative grain boundary energies estimated from these calculations is in a good agreement with experimental data.