Kinetics and mechanism of thermally induced crystallization of amorphous Fe73.5Cu1Nb3Si15.5B7 alloy

• Thermal stabilization of Fe73.5Cu1Nb3Si15.5B7 alloy results in formation of four crystalline phases.
• Kinetic triplets for all crystallization steps have been determined.
• Activation energy for the formation of the latter two phases is significantly higher.
• Crystallization mechanism of all phases was determined, as well as role of impingement.
• Impingement plays an increasingly significant role as the crystallization progresses.

Thermal stability of amorphous Fe73.5Cu1Nb3Si15.5B7 alloy and its crystallization kinetics and mechanism have been investigated. The alloy is stable up to 748 K, after which it undergoes multi-step crystallization with formation of α-Fe(Si)/Fe3Si, Fe2B, Fe16Nb6Si7, and Fe2Si 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 exponents 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 α-Fe(Si) and Fe2B phases, and interface-controlled growth of Fe16Nb6Si7 and Fe2Si phases, impingement plays an increasingly significant role as the crystallization progresses. The determined value of kinetic triplet was used to calculate the alloy lifetime, showing its resistance against crystallization.