Exploring the influence of heat treatment and cooling rate on the magnetic and electronic properties of nanocrystalline-based magnetic cores for power electronic applications

Abstract

This study investigates the impact of dwell duration and cooling parameters on the magnetic and electrical properties of toroidal cores made from commercial FN200 nanocrystalline ribbons. The cores, uniform in physical dimensions and subjected to a constant annealing temperature and heating rate (25 °C/min), were annealed for durations of 30 and 60 min at a peak temperature of 560 °C. Subsequent cooling was performed using air, nitrogen, and water. Analysis of the cores included examination of DC and AC hysteresis graphs, inductance (L_s), impedance (Z), and saturation current levels. Empirical findings revealed that cores subjected to nitrogen cooling exhibited higher saturation induction, L_s, and relative permeability (μ_r) compared to those cooled by other means. Conversely, while all samples demonstrated relatively high inductance values ranging from 6 to 12 mH, the sample subjected to water cooling exhibited a higher saturation current level. The study further identified a direct correlation between magnetic and electrical properties and dwell time in the furnace, as well as cooling parameters, despite identical initial conditions. Notably, cores cooled with water displayed superior performance in terms of power losses, particularly at higher frequency ranges (> 100 kHz, up to 50 MHz). These findings underscore the critical influence of annealing and cooling parameters on the performance characteristics of nanocrystalline magnetic cores, offering valuable insights for optimizing their design and application in high-frequency applications.