THE THERMODYNAMIC FACTOR IN INTERDIFFUSION - A STRONG EFFECT IN AMORPHOUS NI-ZR

Simultaneous determinations of the interdiffusivity in amorphous Ni-Zr and of the self-diffusivity of Ni in the same phase permit the determ ination of the thermodynamic enhancement Factor for interdiffusion. Us ing thin compositionally graded films containing an initially thin lay er enriched in Ni-62, the evolution on annealing of the composition pr ofile was determined by Rutherford backscattering spectrometry and tha t of the Ni-62 profile by secondary ion mass spectrometry. The effecti ve thermodynamic factor in a-Ni57Zr43 at 623 K is found to be 33 +/- 8 in the first hour of annealing of an as-deposited him, decreasing on prolonged annealing. This factor, larger than any previously reported, is somewhat in excess of the value expected from the Darken analysis, but does not deviate markedly as has been suggested by recent calcula tions questioning the validity of the mean-field approach in that anal ysis.