Solute diffusion of these Al-substituting elements was investigated in Ni3Al single crystals with the composition Ni75.9Al24.1 over a wide temperature range (figure 11, table 15). The concentration profiles were determined by secondary ion mass spectrometry. The experimental data were analyzed in order to establish the governing diffusion mechanism. A model for the minority component diffusion by anti-structure defects had been suggested for the L12 structure. It involved both nearest-neighbor jumps of the solute atoms on the Ni sub-lattice as anti-structure atoms and the formation of so-called anti-structure bridges which corresponded to jumps between different sub-lattices. The model under consideration was shown to agree with the experimental data on the Al-substituting solute diffusion (X = Ga, Ge, Ti, Nb) in Ni3Al and permitted the observed ratio of the diffusivities DNi/Dx to be explained. These could be higher or lower than unity, depending upon the solute and temperature.

Solute Diffusion of Al-Substituting Elements in Ni3Al and the Diffusion Mechanism of the Minority Component. Divinski, S.V., Frank, S.T., Södervall, U., Herzig, C.: Acta Materialia, 1998, 46[12], 4369-80

Table 14

Grain boundary diffusivity of 67Ga in Ni3Al