Effect of Co substitution for Fe on the non-isothermal crystallization kinetics of Fe80P13C7 bulk metallic glasses

The non-isothermal crystallization kinetics for the first crystallization peak of Fe80-xCoxP13C7 (x= 0, 5, 10, 15, 20 at.%) bulk metallic glasses (BMGs) have been investigated. The results indicate that the Co addition significantly influences the thermal stability, apparent activation energy and crystallization mechanism of Fe80P13C7 BMGs. As the Co replaces the Fe, the thermal stability and apparent activation energy decrease, and the crystallization mechanism changes from the diffusion-controlled growth of pre-existing nuclei to the diffusion-controlled growth of the initial crystal type with a decreasing nucleation rate. Besides, the primary crystalline phase changes from (Fe,Co)(3)(P,C) phase to (Fe,Co)(3)(P,C) and alpha-(Fe,Co) phases. With increasing the Co content, additionally, the apparent activation energy increases and the X-ray diffraction peak strength of alpha-(Fe,Co) phase enhances. The analysis of the local Avrami exponent n for the first crystallization process indicates that the short-range order clusters in the Fe-Co-P-C BMGs can become pre-existing nuclei to promotes the precipitation of (Fe,Co)(3)(P,C) phase, and then the precipitation of (Fe,Co)(3)(P,C) phase further promotes the nucleation of alpha-(Fe,Co) phases.