Effects of Si/B ratio on the isothermal crystallization behavior of FeNiSiBCuNb amorphous alloys

Abstract

In the present work, (Fe40Ni40SixByCu1)0.97Nb0.03 (Si/B = 1:1, 1:2, and 1:3) alloys were prepared by the as-melt spun method. The effect of different Si/B ratios on the isothermal crystallization behavior of FeNiSiBCuNb glass alloys were investigated. The activation energies of the Si/B = 1:1, 1:2, and 1:3 alloys for nucleation and grain growth were calculated by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model as 123.6 kJ/mol and 207.3 kJ/mol, 151.0 kJ/mol and 251.3 kJ/mol, and 88.6 kJ/mol and 170.0 kJ/mol respectively; hence, crystal nuclei needed to cross a higher energy barrier in the growth process. The variation of local Avrami exponent n(α) with crystallization fraction α demonstrates that the crystallization mechanism was divided into three stages: i: initial crystallization stage with n＞2, indicating that α-Fe(Si) phase or γ-(Fe, Ni)Si phase with a high nucleation rate stage, ii: middle crystallization stage with n≈2, indicating that FeNiB phase with a stable nucleation stage, and iii: the end of crystallization stage with n＜2, indicating that γ-(Fe, Ni)Si and FeNiB phases with a growth stage; The crystallization process was transformed from diffusion-controlled one-dimensional growth to diffusion-controlled three-dimensional growth.