Solute diffusion of Al-substituting elements in Ni3Al and the diffusion mechanism of the minority component

Solute diffusion of Al-substituting elements (Ga, Ge, Ti, and Nb) has been investigated in Ni3Al single crystals with the composition Ni75.9Al24.1 in a wide temperature range. The concentration profiles were determined by secondary ion mass spectrometry (SIMS). The experimental data were analyzed to establish the governing diffusion mechanism in this compound. A model for the minority component diffusion by anti-structure defects has been suggested for the L1(2) structure. It involves both nearest-neighbor jumps of the solute atoms on the Ni sublattice as anti-structure atoms and the formation of so-called antistructure bridges which correspond to jumps between different sublattices. The model under consideration was shown to agree with the experimental data on the Ai-substituting solute diffusion (X = Ga, Ge, Ti, Nb) in Ni3Al and it allows the observed ratio of the diffusivities D-Ni/D-x to be explained. which may be higher and/or lower than unity depending on the solute and temperature. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.