EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Ultrafine grained (UFG) or even nanocrystalline (NC) materials feature interesting functional properties due to their refined microstructure. Focussing on magnetic properties, strong microstructural influences can e.g. be found for the coercive field dependence or the occurrence of exchange coupling phenomena between phases of different magnetic properties. As it is well known, severe plastic deformation using high pressure torsion (HPT) is an elaborate method to transform coarse-grained, bulk materials into a refined microstructural state. Starting from binary or ternary powder mixtures, UFG / NC single phase materials or multi-phase nanocomposites are produced. Metastable supersaturated states can also be the result of HPT, making the investigation of thermal stability necessary.
For the presented investigations, binary and ternary powder mixtures with varying fractions of ferromagnetic and non-ferromagnetic elements were pre-compacted and severe plastically deformed using HPT. Regarding the analysed functional properties, focus is laid on magnetostriction and (giant-) magnetoresistance, both seriously depending on the microstructure. While a nanocomposite involving small and non-percolating ferromagnetic particles results in a material exhibiting giant magnetoresistance, a supersaturated state of appropriate materials results in a high saturation magnetostriction – higher than the one of the individual materials. The processed materials are investigated with X-ray techniques, atom probe tomography and electron microscopy and the consequences of the choice of initial metal powders, their ratio and co-deformability on the resulting as-deformed microstructure will be discussed. Furthermore, the interplay of the as-deformed and annealed microstructures with the above-mentioned magnetic properties is examined.

This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant No. 757333).