Thermochimica Acta 584 (2014) 1–7 Contents lists available at ScienceDirect Thermochimica Acta j ourna l h om epage: www.elsevier.com/locate/tca Kinetics and mechanism of thermally induced crystallization of amorphous Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy Milica M. Vasi ´ c a , Duˇ san M. Mini ´ c b , Vladimir A. Blagojevi ´ c a , Dragica M. Mini ´ c a,∗ a Faculty of Physical Chemistry, University of Belgrade, Serbia b Military Technical Institute, Belgrade, Serbia a r t i c l e i n f o Article history: Received 6 February 2014 Received in revised form 20 March 2014 Accepted 22 March 2014 Available online 29 March 2014 Keywords: Amorphous alloy Crystallization kinetics Crystallization mechanism Impingement Anisotropic growth a b s t r a c t Thermal stability of amorphous Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy and its crystallization kinetics and mechanism have been investigated. The alloy is stable up to 748 K, after which it undergoes multi-step crystalliza- tion with formation of -Fe(Si)/Fe 3 Si, Fe 2 B, Fe 16 Nb 6 Si 7 , and Fe 2 Si crystalline phases. The crystallization occurs in two distinct and well separated complex processes, each corresponding to formation of two phases. Activation energy for the formation of the latter two phases is significantly higher, due to their formation out of the previously formed iron–silicon crystalline phase. By comparison of Avrami expo- nents of experimental system and a hypothetical system where no impingement occurs, the influence of impingement on reaction mechanism was successfully isolated. While the reaction mechanism was suggested as volume diffusion controlled growth of -Fe(Si) and Fe 2 B phases, and interface-controlled growth of Fe 16 Nb 6 Si 7 and Fe 2 Si phases, impingement plays an increasingly significant role as the crys- tallization progresses. The determined value of kinetic triplet was used to calculate the alloy lifetime, showing its resistance against crystallization. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Amorphous alloys (metallic glasses) have been widely studied in the last fifty years due to their favorable physical, chemical and mechanical properties which make them useful for various applications, such as: power devices [1,2], information handling technologies [3], magnetic sensors [4], anti-theft security systems [5], etc. These materials are thermodynamically and kinetically metastable and tend to transform to more stable form under cer- tain conditions including high pressure and high temperature, or prolonged activity at moderate temperature. Structural transfor- mations occurring during structural stabilization process include structural relaxation, crystallization and recrystallization, which can result in loss of technologically favorable properties, or forma- tion of hybrid nanocrystalline/amorphous structure with targeted functional properties. Therefore, their region of stability, as well as the mechanism and kinetics of structural transformation are very important characteristics. Due to importance of crystalliza- tion kinetics for development of amorphous and nanocrystalline materials, kinetics of crystallization of amorphous alloys has been studied extensively [6–11]. ∗ Corresponding author. Tel.: +381 11 332 2883. E-mail address: drminic@gmail.com (D.M. Mini ´ c). Three-dimensional atom probe analysis of various stages of crystallization in the amorphous Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloy [12] revealed that Cu-clusters were formed prior to the onset of the pri- mary crystallization and then served as heterogeneous nucleation sites for the crystallization of the Si-enriched -Fe phase. Examina- tion of amorphous Fe–Si–B–Nb–Cu rod alloy [13] showed multistep crystallization process, which included precipitation of -Fe phase in the first step, followed by transformation of -Fe-amorphous to multicomponent system including -Fe, Fe 23 B 6 , Fe 2 B, Fe 3 Si and Fe 2 Nb crystalline phases in the second crystallization step. Study of amorphous-to-nanocrystalline transformation in an amorphous system with composition Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 [14] revealed slow decrease of electrical resistivity during nanocrystallization process, as well as changes in nanocrystallization kinetics from a JMA-like to an essentially power-law kinetics [14], but without explanation for such kinetic behavior. Influence of thermally induced structural transforma- tions on functional properties of ribbon shape amorphous Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy has been a subject of intense research in our group [15–19]. Detailed study of its crystallization revealed multi-step process which included formation of different iron- phases and resulted in changes in functional properties. A combination of XRD and Mössbauer data showed that complex crystallization of this alloy involved, beside formation of stable phases, a number of metastable intermediary phases, which http://dx.doi.org/10.1016/j.tca.2014.03.028 0040-6031/© 2014 Elsevier B.V. All rights reserved.