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Grain boundary diffusion and precipitates in B2 Ti−50.2 at.% Ni alloy
Grain boundary diffusion of 44Ti and 63Ni in the B2 Ti−50.2 at.% Ni polycrystalline alloy was measured in Harrison's B regime (573−923 K) using the radiotracer technique. The triple product P = sδDgb (s is the segregation factor, δ the grain boundary width, and Dgb the corresponding grain diffusion coefficient) for Ti and Ni was determined. Although the absolute values of the triple products P are typical for the B2-ordered alloys, both Ti and Ni GB diffusion in NiTi reveals a unique behavior with significant deviations from a linear Arrhenius-type temperature dependence. Transmission electron microscopy analysis of GB structures at 673 K and 923 K substantiated the occurrence of different interface types which may provide the slower and faster grain boundary diffusion paths in agreement with the experimental data. The influence of different types of precipitates on grain boundary diffusion and possible diffusion mechanisms in the different regimes are discussed.