Study On The Crystallization Behavior And Properties Of FeZrB Soft Magnetic Amorphous Ribbons

Nanoperm alloy is a kind of soft magnetic materials exhibiting excellent magnetic properties, and has a potential application prospect in future. However, the industrialization manufacturing technique of Nanoperm alloy should be further developed. Therefore, in the present study, Fe₇₈Zr₇B₁₅ (at.%) alloy is chosen to prepare amorphous ribbons under different process conditions. In addition, the annealing is carried out to investigate the influence of annealing process on the structure, phase morphology and soft magnetic properties of the ribbons. The optimized annealing process is obtained. The nucleation and growth modes during the annealing processed are discussed by means of crystallization kinetics, which will offer significant directions for annealing design. The major contents of this thesis are summarized as follows:1) The as-quench ribbons are perpared in different conditions and their corresponding crystallization structure, ribbon thickness and magnetic properties are characterized. The results show that the as-quench ribbons are fully amorphous structure. The crystallization process is studied by annealing the ribbons in vacuum. The influence of annealing temperature and time on the structure, toughness, phase morphology and magnetic properties of the ribbons are also discussed. The achieved optimized annealing process is that the ribbons should be annealed at 550℃for 20min. During this process, the first step of crystallization occurs andα–Fe/amorphous dual phase structure forms. It is found that in this step the nanocrystallineα–Fe grains are produced and dispersed in the matrix.2) During the annealing process, it needs about 30min for the temperature of the furnace reaches 550℃at a heating rate of 18.3℃/min. Therefore, in order to study the nucleation and growth modes of the primaryα–Fe during this process, the crystallization mechanism both in continuous heating and isothermal conditions are discussed. The apparent activation energy for the crystallization of the ribbons is calculated by Kissinger and Ozawa equations. In contrast, the local activation energy in continuous heating and isothermal conditions are respectively obtained by Kissinger–Akahira–Sunose (KAS) and Arrhenius equations. Futhermore, Johnson–Mehl–Avrami–Kolmogorov (JMAK) is used in isothermal conditions and also extended to continuous heating conditions to probe the local Avrami exponent by which the crystallization mechanism can be illustrated.3) It is found that for the process of annealing at 550℃for 20min under vacuum, the nucleation and growth modes of primaryα–Fe grains are mainly dominated by isothermal process. The process is deemed a surface nucleation and growth process with nucleation rate decreasing with time. The saturation magnetization increases with increasing the volume fraction ofα–Fe phase. In order to prohibit the deterioration of soft magnetic properties caused by the growth ofα–Fe grains, the annealing should be controlled at lower temperature and short time to employing high rate annealing.