Some properties of a nanocrystalline Ni-P alloy and an amorphous alloy of the same chemical composition, including the thermal expansion coefficient, specific heat capacity, electrical resistance and thermal stability, are experimentally measured and compared. The results show that the properties of the nanocrystalline alloy are very different from those of the amorphous alloy.
In order to obtain extremely fine-grained microstructures by crystallization of the metallic glass, the nucleation and growth processes of the crystalline phases have been investigated over a wide temperature range. Analysis of the transformation kinetics and microstructure has allowed determination of the nucleation and crystal growth rates. The parabolic growth rate increases with annealing temperature, and the nucleation rate based on the homogeneous nucleation theory has shown a maximum at an intermediate temperature range. To a certain extent, quenched-in nuclei influence the crystallized microstructures. In this paper, we have also performed an investigation to determine the effect of quenching rate on the grain size and its distribution. The results indicate that the number of crystals per volume unit formed during isothermal annealing depends not only on annealing time and temperature, but also on the quenching rate, that is the number of quenched-in nuclei of the as-quenched amorphous alloy. The results obtained have shown that it is possible to achieve an extremely fine-grained and well-distributed microstructure by controlling the quenching rate and following crystallization of the metallic glass under suitably chosen annealing conditions.
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