Thermal Vacancy Formation and Self-Diffusion in IntermetallicFe3SiNanocrystallites of Nanocomposite Alloys

Combined high-temperature studies of positron lifetime and ${}^{59}\mathrm{Fe}$ tracer diffusion show thermal vacancy formation and rapid self-diffusion in the nanocrystallites of intermetallic-amorphous ${\mathrm{Fe}}_{73.5}{\mathrm{Si}}_{13.5}{\mathrm{B}}_9{\mathrm{Nb}}_3{\mathrm{Cu}}_1$ nanocomposites. In combination with an intergranular amorphous phase and densely packed interfaces between these interlayers and the nanocrystallites the unique behavior arises where self-diffusion in interfacial regions is slower than in crystallites. Slow atomic ordering processes during crystallization are ascribed to low diffusivities on the Si sublattice of the nanocrystallites.