Effect of mechanical deformation and microstructural evolution on the magnetic Composite performance of Soft Magnetic Composite components

Abstract

Soft Magnetic Composite (SMC) components designed for electromagnetic applications are being produced based on traditional Powder Metallurgy (PM) techniques. The latter provide profitable and sustainable production routes that yield net-shaped parts, optimizing the number of post-operations after compaction besides annealing processes. The concept of SMC technology is based on encapsulating each individual iron particle with a thin electrically insulating surface coating and subsequently pressing them together in a three dimensional array to form a finished compact. In this manner, uniform and isotropic 3D magnetic properties are acquired that offer design freedom in creating unique and innovative application concepts, as opposed to the more traditionally used laminated steels. The SMC products exhibit improved magnetic performance for a wide range of frequency applications, due to the fact that they offer higher bulk electrical resistivity by effectively confining the deleterious effects of core losses, especially in high frequency applications. Equally important to the insulating coating is the microstructure of the SMC parts and its evolution thorough the manufacturing process. Investigations on this context are important as to improve and tailor the process in producing parts of desired properties. The objective of this thesis work was to implement techniques and methods that would provide valid information on the microstructural evolution and magnetic behaviour of SMC along different steps of the production process. The development of internal microstructure and grain orientation of the powder particles under different processing conditions has been assessed by means of Electron Backscatter Diffraction (EBSD) technique, emphasizing the degree of mechanical deformation based on misorientation maps, as well as the subsequent recovery and recrystallization of the components. Additional mechanical tests done by nanoindentation have been correlated to the EBSD analysis, in order to quantify the degree of contribution of the aforementioned factors to the magnetic properties of the SMC parts. The contribution from factors related to particles characteristics, i.e. grain size and amount of plastic strain were also investigated and the results were correlated to the magnetic behaviour.