Diffusion in amorphous NiZrAl alloys

Tracer diffusion coefficients for large and small sized impurities were measured in the bulk metallic glass Ni_xZr_yAl_z for several compositions. Molecular beam deposition was employed to grow thin films and secondary ion mass spectrometry was used to determine the concentration-depth profiles of several tracers. A dependence of the atomic mobility of the tracer on its size was found, as observed in the binary Ni_xZr_y amorphous alloy system. The presence of the Al reduces the diffusion coefficients in general, with a stronger decrease for the small sized tracer. The results support the existence of two different diffusion mechanisms proposed for amorphous metallic alloys.