Superior Mechanical and Magnetic Performance of Highly Anisotropic Sendust‐Flake Composites Freeze Cast in a Uniform Magnetic Field

Abstract

Despite extensive research, the manufacture in the bulk of high‐performance flake‐based magnetic composites with a highly aligned, nacre‐like structure remains challenging. Many challenges can be overcome by freeze casting in an externally applied, uniform magnetic field, which causes both the flakes and the composite walls of the cellular solid to align parallel to the B‐field lines. When appropriately sized, the flakes experience a second alignment parallel to the freezing direction because of a shear flow that occurs due to both the volumetric expansion of the ice phase and mold contraction during the directional solidification. The resulting orthotropic structure of the freeze‐cast magnetic composite is reflected in orthotropic mechanical and magnetic properties of the material. The magnetic composites manufactured by magnetic‐field assisted freeze casting outperform by a factor of 2–4 in terms of stiffness, strength, and toughness materials that are processed in the absence of a magnetic field and do not exhibit a monodomain architecture. Because of the highly aligned microstructure, it is possible to compact the initially lamellar composite with 90% porosity to at least 80% strain. The results presented in this study illustrate the tremendous potential for magnetic freeze casting of magnetic composites for use in power conversion.

Phase-field modeling of microstructure evolution: Recent applications, perspectives and challenges

“…metallic foams [389,390]). The PF method also provides an outstanding tool to predict and control the development of micro-/nanopatterned materials, such as nano-templated eutectics [391] or ice-templated structures [392] for instance used in biomedical applications [393] or manufacturing of magnetic composites [394]. Furthermore, phase-field simulations can help understanding the formation of complex hierarchical biomaterials with outstanding properties [395] (e.g.…”

High Energy Absorption Nacre‐Like Calcium Silicate Hydrate (C‐S‐H) Composite Toward Elastic Cementitious Materials

“…Nacre is a striking model from nature with remarkable strength and toughness due to the ingenious hierarchical structure and precisely designed interfaces. [19] Various kinds of artificial nacre-like composite have been replicated by mimicking its architecture using creative methods such as freeze casting, [20] layer-by-layer deposition, [21] electrophoretic deposition, [22] or mechanical assembly. [23] Inspired by the exquisite hierarchical structure of nacre, herein, we develop a highenergy absorption C-S-H composite with highly ordered laminar microstructure by an upscaled and robust fabrication method.…”

Nacre‐Inspired, Efficient, and Multifunctional Soft Magnetic Composites by Cold Sintering Design

“…[1,2] To meet the sustainable demand of miniaturization, high efficiency, and high frequency for the electrified world, Internet of Things (IoT), and 5Gþ, it is urgent to develop novel SMCs with large permeability and saturation flux density, low coercivity, together with high operation frequency, thermal stability, and mechanical strength. [3][4][5] Herein, high permeability and saturation flux density of SMCs are important for reducing device sizes. [6] Take power converters as an example; the former gives rise to less coil turns, while the latter allows for the use of a smaller magnetic core to handle higher power.…”

“…One of the effective strategies for improving the comprehensive performance of the SMCs is using the layered arrangement of insulating coated magnetic flakes. [4,5,[11][12][13] Compared with granular magnetic particles, magnetic sheets are beneficial for reducing the demagnetizing factor and skin effect. [12,14] Therefore, enhanced magnetic properties and high-frequency performance can be expected in the SMCs with layered microstructures.…”

“…[15] Furthermore, recent investigations indicate that nacre-like structure shows the advantage of achieving improved comprehensive performance of the SMCs. To date, various methods have been applied to fabricate nacre-like materials, which are but not limited to freeze cast, [5,[16][17][18] layer-by-layer assembly, [4,19,20] spray coating, [21] mineralization, [15] spatially regulated cracking, [22] magnetic particle alignment, [23,24] 3D printing, [25] shear-flow-induced alignment, [26] hot pressing, [27] or combining some of them. It should be noted that large-scale (especially large thickness) and efficient fabrication of 3D bulk nacre-like "brick walls" still remains a challenge.…”