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 Ni75.9 Al24.1 in a wide temperature range. The concentration profiles were de termined by secondary ion mass spectrometry (SIMS). The experimental d ata were analyzed to establish the governing diffusion mechanism in th is compound. A model for the minority component diffusion by anti-stru cture defects has been suggested for the L1(2) structure. It involves both nearest-neighbor jumps of the solute atoms on the Ni sublattice a s anti-structure atoms and the formation of so-called antistructure br idges which correspond to jumps between different sublattices. The mod el under consideration was shown to agree with the experimental data o n the Ai-substituting solute diffusion (X = Ga, Ge, Ti, Nb) in Ni3Al a nd it allows the observed ratio of the diffusivities D-Ni/D-x to be ex plained. which may be higher and/or lower than unity depending on the solute and temperature. (C) 1998 Acta Metallurgica Inc. Published by E lsevier Science Ltd. All rights reserved.