Characterization of dislocation structures associated with small-angle boundaries in annealed L1 Ni Ge

Abstract

The dislocation structures in small-angle tilt and mixed-character grain boundaries formed during the high-temperature annealing treatment of an L1 intermetallic alloy (Ni Ge) have been characterized by transmission electron microscopy. The microscopy observations, under weak-beam imaging conditions, have conclusively shown that the superdislocations comprising the boundaries are narrowly dissociated on the {001} and {111} planes, with {001} and {113} being the respective contact planes for the tilt and mixed character boundaries. The antiphase-boundary (APB) energies have been calculated by using the force balance equation of Marcinkowski given in 1968, which is based on isotropic elasticity, and by balancing the forces for an isolated dissociated superdislocation using both isotropic and anisotropic elasticity. The values of APB energies obtained by these three methods are essentially the same for both {001} and {111} planes provided that the image shifts inherent during weak-beam imaging are accounted for. In comparison with what has been observed in Ni Al, the similarity of these measurements suggests that anisotropic elasticity plays a reduced role in determining the dissociation distance in Ni Ge. Moreover, the values are in good agreement with those previously obtained after room temperature deformation by Balk et al. in 1997, which suggests that there is no appreciable dependence of the cube plane APB energy on temperature in Ni Ge.