Phase-Separation Behavior of Electrodeposited Ni-P Amorphous Alloys

Phase-separation behavior of the Ni-P amorphous alloys was studied by a differential scanning calorimeter (DSC), a transmission electron microscope (TEM), small-angle X-ray scattering (SAXS) and a magnetic balance. The phase separation occurs in the composition range of about 8∼12 wt% phosphorus prior to the crystallization. From the analyses of the SAXS data by Guinier’s approximation or Porod’s law, it is suggested that two types of phase separation take place during aging; Ni-9.4 wt%P alloy decomposes to an interconnected structure of a Ni-rich zone and a P-rich zone apparently by a mechanism of spinodal decomposition, while Ni-11.5 wt%P alloy forms fine particles (ca. 5∼10 nm) of fcc nickel in an amorphous matrix by a homogeneous nucleation and growth mechanism. The results of magnetizatin measurements also support the occurrence of two types of phase separation in the aged alloys. After the phase separation, the P-rich amorphous phase directly transforms to an equilibrium state by forming a stable Ni3P crystal.