Abstract
The crystallization processes and kinetics of amorphous Ni-9.4wt%P, Ni-11.5 wt%P and Ni-14.4 wt%P alloys were studied by differential scanning carolimetry, electron microscopy, and optical microscopy. Hardness measurements were also performed to follow the crystallization process. The crystallization mechanism of Ni-9.4 wt%P and Ni-11.5 wt%P alloys is a heterogeneous nucleation of tetragonal Ni3P in an amorphous matrix and its spherical growth, and that of Ni-14.4 wt%P alloy is a heterogeneous nucleation of a metastable crystal and its stacking lamellar growth. The apparent activation energies for the crystallization were 240kJ/mol (Ni-9.4wt%P), 249kJ/mol (Ni-11.5 wt%P), and 201kJ/mol (Ni-14.4 wt%P). The values of the Johnson-Mehl-Avrami's time index, n, for the crystallization were abut 3.1 (Ni-9.4 wt%P), 3.2 (Ni-11.5 wt%P), and 2.5 (Ni-14.4 wt%P). The experimentally observed relationship between hardness of the alloy and aging time and temperature was in good agreement with the calculated one using the kinetic parameters, that is, activation energy and frequency constant for the crystallization.
