Nanostructured transformation mechanism of amorphous Fe-B-Si alloys by the crystallization method

Abstract

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.

The peculiarity of contraction in the primary crystallization of amorphous Fe73.5Nb3Cu1Si13.5B9 alloy

“…Since K A and K B fall into the same order of magnitude [17,16] and t A is larger than t B , D A is much smaller than D B . The reason is that Nb increases the energy barrier to the diffusion of Fe atoms.…”

“…So, the growth process can be expressed as follows: where D is the diffusion coefficient and K is a constant. It is known that the mean size of ␣-Fe primary crystallization grains of Alloy A is 10-20 nm [1,9] and that of Alloy B is about 0.5 m [15,16] and the radius of the grains acts as the diffusion distance, Eq.…”