Kinetics of primary crystallization of hypoeutectic amorphous Ni–P alloy studied by in situ ASAXS and DSC

Abstract

The primary crystallization of amorphous Ni 83P 17 alloy was studied by in situ anomalous small-angle scattering (ASAXS) and differential scanning calorimetry (DSC). ASAXS, DSC and X-ray diffraction experiments show that only one process, the primary crystallization, proceeds at 250 °C for annealing times up to 18 h. The volume fraction and the average composition of the precipitating Ni-rich particles were determined from the ASAXS data. The volume fraction as a function of the annealing time was compared with the transformation rate determined from the DSC heat flow. The two methods differ significantly only for annealing times shorter than 100 min. The average particle composition differs from the final one also for this period. The Avrami plot is not linear for the integrated DSC heat flow, but it is linear for the volume fraction determined by ASAXS. The nucleation rate determined by ASAXS was used to calculate the extended volume in the Kolmogorov–Johnson–Mehl–Avrami theory. The ASAXS results are consistent with the KJMA theory. The primary crystallization of the amorphous Ni 83P 17 alloy proceeds by precipitation of Ni-rich particles by diffusion controlled mechanism and decreasing nucleation rate. The effective diffusion coefficient is close to that of B in the similar amorphous Fe–B alloy.