A TRANSIENT NUCLEATION MODEL FOR SOLID-STATE AMORPHIZATION

Solid state amorphization in diffusion couples is analyzed with particular reference to the Ni-Zr system. We show that there is no nucleation barrier for formation of the first phase, and discuss why that phase is amorphous. We postulate that formation of the second product phase (a crystalline intermetallic compound) is suppressed by consumption of sub-critical clusters of that phase by the growing amorphous layer. We derive approximate expressions for the critical thickening rate of the amorphous phase (above which suppression is possible), and for the maximum thickness that the phase can attain before the crystalline compound nucleates.