Calculation of crystal growth in 5BDSR amorphous alloy during heat treatment

The crystal growth in 5BDSR (Fe73.5Cu1Nb3Si13.5B9) amorphous alloy was calculated, taking into account thermal and diffusion processes occurring in the amorphous alloy and in a growing crystal during heat treatment. The thermal and chemical processes at the crystalline-amorphous phase boundary were taken into consideration. The crystallization of a multicomponent metal solution was considered by using growth of a single particle as an example. At the initial stage, each crystal grew surrounded by a non-crystalline phase. The shape of the growing nucleation center was accepted to be spherical. A spherical coordinate system was chosen, with the origin at the center of the growing particle. The whole system was also spherical. The initial distribution of the parameters of system state (component concentrations, rates, temperature, and other values) possesses spherical symmetry. At any time, the distribution of all parameters characterizing the system of values also has spherical symmetry. The system has three sections: the non-crystalline phase, the growing particle (the crystalline phase), and, separately, the interface of these phases. The calculation of the crystal growth was carried out in the temperature range between 450 and 700 °С and the holding time of one hour. Intensive growth began 0.6 seconds after the start of holding. Within one hour, the crystal diameter increased to 7.0 nm at 450 °С and to 20 nm at 630 °С. During growth, the concentration of Fe before the crystal growth front decreased to 0.15 % within 60 minutes. At the same time, the concentration of Nb increased up to 90 %. The content of the remaining components remained virtually the same. Sharp decrease in the concentration of Fe in the amorphous phase at constant concentration of Si led to decrease in Fe content in the crystalline phase. Calculation results were compared to experimental data.