Speaker
Description
Technological demand for soft magnetic materials capable of operation at high temperatures has led to an increased interest in FeCo-based nanocrystalline alloys. Magnetic components in various energy conversion devices and sensors are during their operation often exposed to high temperature environments, which could have a marked impact on their performance. Therefore, a better knowledge about stability of functional properties if the soft magnetic materials are used at elevated temperatures is of high importance for estimation of their application potential. In this work, the effects of rapid annealing (RA) on soft magnetic properties at elevated temperatures were investigated in series of high-Bs Fe-(Co)-B-(Cu) alloys prepared by planar flow casting. A special attention was given to rapid annealing technique that utilizes a compression of samples between pre-heated Cu blocks. This technique allows to obtain soft magnetic nanocrystalline alloys with reduced content of non-magnetic elements exhibiting attractive combination of high saturation magnetic flux density ($B_{s}$) and low coercivity ($H_{c}$) [1,2]. The as-quenched amorphous ribbons were subjected to rapid annealing for 0.5 s at temperatures between 480-500°C, which were identified as optimum RA heat treatment conditions. A more detailed description of the rapid annealing setup used in our study can be found in [3]. The second batch of amorphous ribbons was conventionally annealed (CA) in the vacuum furnace for 60 minutes at temperatures close to their first crystallization peak temperature determined by DSC calorimetry. We show that very high heating rates and short processing times during RA resulted in a formation of rather small nanocrystalline grains with typical sizes in the range of 10-15 nm. The observed grain refinement has led to a marked reduction of coercivity as compared to conventionally annealed samples Our main attention was focused on the characterization of soft magnetic properties of RA samples at elevated temperatures. The hysteresis loops were collected from room temperature (RT) up to 673 K using the Förster type B-H loop tracer with a built-in furnace placed inside the magnetically shielded room. Reference hysteresis loop were also collected at RT after each high temperature measurement. Our experiments revealed that rapidly annealed high-$B_{s}$ Fe-(Co)-B-(Cu) alloys exhibit very good thermal stability of soft magnetic characteristics up to 623 K, which makes them promising soft magnetic materials for applications at elevated temperatures.
Acknowledgements
This work was supported by the projects APVV-19-0369, VEGA 2/0148/23 and JRP NOMAGRAD.
References
[1] K. Suzuki, R. Parsons, B. Zang, K. Onodera, H. Kishimoto, and A. Kato, “Copper-free nanocrystalline soft magnetic materials with high saturation magnetization comparable to that of Si steel,” Applied Physics Letters, vol. 110, no. 1. 2017. doi: 10.1063/1.4973772.
[2] B. Kunca, J. Marcin, R Parsons, P. Švec, P. Švec sr., K. Suzuki, I. Škorvánek, “Soft magnetic performance of ultra-rapidly annealed high-Bs Fe-(Co)-B nanocrystalline alloys at elevated temperatures”, J. Alloy. Compd. vol. 911, 16503, 2022. doi: 10.1016/j.jallcom.2022.165033.
[3] B. Kunca, J.Marcin, P. Švec sr., I. Škorvánek, “Thermal stability and magnetic properties of the nanocrystalline (Fe64Co21B15)99Cu1 high-Bs alloy at elevated temperatures”, J. Magn. Magn. Mater. vol. 591, 171679, 2024. doi: 10.1016/j.jmmm.2023.171679.
