Hysteresis design by nanostructural-engineering through continuous forming processes

Collaborative Research Centre/Transregio (CRC/TRR) 270 I Subproject A09

Objective

In the Collaborative Research Centre Transregio 270 – “Hysteresis design of magnetic materials for efficient energy conversion (HoMMage)”, materials scientists, chemists, physicists and engineers are collaborating in the researches into magnetization mechanisms and the development of novel permanent magnetic and magneto-caloric materials. Following the goal of the entire SFB/TRR, a new manufacturing process for magnetic materials by forming is being developed within the framework of subproject A09, with which materials with adjustable nanostructure can be produced.

Motivation

Permanent magnetic materials play an increasingly important role for technologies in the fields of energy generation, mobility, as well as in automation and entertainment industry. The production of permanent magnets has taken a strong upturn in the last decade, and the demand for magnets has increased dramatically due to the increasing automation, as well as the change from combustion engines to electro mobility.

The microstructure of the material is crucial for the permanent magnetic properties. In the permanent magnetic material, the main phase (grains) should be surrounded respectively magnetically decoupled by another phase (grain boundary). Both phases should have certain properties to induce magnetization mechanisms, such as domain-wall-pining or nucleation. In addition, numerous parameters, such as the orientation and size of the grains and the thickness of the grain boundary, have an effect on the magnetic properties.

Current approaches of investigating and manufacturing micro- or nano-structural functional materials are based on melt or powder metallurgy as well as chemical synthesis. These methods are only applicable to specific alloys or material combinations, as they are depending on the phase diagram or chemical properties. Dimensions of the microstructures are also limited by these methods.

Fig. 1 Concept of forming metal-matrix-composite for magnetic materials

Forming of so-called Metal-Matrix-Composites (MMCs) presents a promising solution to overcome these limits. MMCs consist of a matrix and at least one other different material embedded into the matrix. Our MMCs are composed of wires and a surrounding matrix material. The wires have the composition of the main phase of the magnetic material and are transferred to the desired nanostructure during the forming operations. They are surrounded by a shell material in the form of bundled wires or matrix or coating, which represents the second phase or rather grain boundary phase in the targeted nanostructure. The initial rods are continuously formed into wires with significantly smaller diameters. These new wires are once again bundled into rods and formed into wires again. This step will be repeated until the microstructures of the wires have reached the desired dimension, as it shown in Fig. 1.

The approach of engineering the nanoscale MMC cross-sectional structure opens a novel route to investigate in detail the curing mechanisms of nucleation and domain-wall-pinning through the scalability of nanostructure design. At the same time, the mechanisms of plastic deformation and grain refinement of non-conventional forming materials are investigated.

Acknowledgment

The project is funded by “Deutsch Forschungsgemeinschaft” (DFG) in terms of the Collaborative Research Centre/Transregio (CRC/TRR) 270 – “Hysteresis design of magnetic materials for efficient energy conversion (HoMMage)”.