Electromagnetic assisted thermal processing of amorphous and nanocrystalline soft magnetic alloys: Fundamentals and advances

Controllable and fast heating profiles provide unique capabilities to realize enhanced soft magnetic properties of amorphous and nanocrystalline materials in conventional nanocrystalline alloys, as well as alloy chemistries for which carefully controlled annealing processes play a critical role in realizing desired properties tailored within a large degree of flexibility. This review aims to identify the fundamental physical phenomena in rapid thermal processing of amorphous and nanocrystalline soft magnetic alloys and to provide a comprehensive summary on the progress made to improve their performance, with an emphasis on processing in electromagnetic fields. The review begins with general background on fundamental concepts of electromagnetic heating and aspects of heat transfer followed by a detailed description of rapid thermal processing techniques employed over the relevant frequency range. These include; Joule heating, induction heating, microwave heating, and laser-assisted surface heating. In addition, traditional methods enabling high heating rates are included and reviewed accordingly. Influences of processing parameters and the detailed mechanism of heating are discussed with an assessment of experimental observations reported in the literature and further validated by simulations. Phase transformations and crystallization processes are discussed in the context of nucleation and growth kinetics, with a demonstration of thermal processing routes and alloy design. A critical evaluation of structural and magnetic properties are provided, and the underlying role of heating rates and magnetic anisotropies are highlighted. An outlook for future development trends and a number of challenges in this field are presented. (C) 2020 Elsevier B.V. All rights reserved.