Magnetic and Morphological Characterization of SrFe12O19/PA12 Composites: Hard-Magnetic Filament for Magnetic Field Assisted Additive Manufacturing (MFAAM)
Magnetic polymer composites are being investigated for applications such as permanent magnets, transformers, electrical machines, and magnetic shielding. The particles are dispersed in a polymeric matrix to allow for the realization of magnetic parts of any form with reduced manufacturing cost and weight without significantly sacrificing their magnetic behavior. Materials are manufactured through additive manufacturing (AM) processes such as Fused Filament Fabrication (FFF) to allow for rapid prototyping and highly complex designs compared to magnetic composites manufactured through conventional methods. However, the major concern of permanent magnet AM is, no commercial hard-magnetic 3D-printer filament is yet on the market. In our work, we manufacture and characterize magnetic polymer composite 3D-printer hard magnetic filament for the development of the Magnetic Field Assisted Additive Manufacturing (MFAAM) technology. The magnetic filaments are made by adding different wt.% of SrO(Fe2O3)6 powders into polyamide-12(PA12) using a twin-screw extruder. In MFAAM 3D printing, an external magnetic field is applied during the printing process, which allows an in-situ magnetic pre-alignment of particles in the molten composite and the magnetic particles to be oriented in a well-defined direction resulting in the realization of magnetic structures with complex well-defined easy axis distributions. This realizes field induced magnetic anisotropy during the extrusion and increases remanence, thus yielding stronger permanent magnets. In this dissertation, we investigate the magnetic hysteresis, magnetic viscosity and magnetic anisotropy of our manufactured composite pristine and field-annealed filaments by a vector Vibrating Sample Magnetometer (VSM). To my best knowledge, these are the first vector magnetic viscosity measurements reported on in literature. The magnetic viscosity is largest along the easy direction. The hysteresis measurements of pristine filaments show that they have a wire texture originating from the flow of the molten composites during the extrusion process. The texture of 3D printed filaments is more complex and originates from shear flow contributions in the extrusion nozzle and in between the moving nozzle and the stationary printer bed. The magnetic properties of field annealed and MFAAM samples were studied to further the development of the MFAAM deposition process. The objective was to better understand how melt viscosity and packing fraction affect non-spherical particle alignment processes. field-annealed and MFAAM samples have their easy axis parallel to the anneal or print field direction, hence, show strong anisotropy. In this dissertation, a new method is presented to study the rotation of the magnetic particles in a molten suspension using a biaxial VSM. Modelling calculation and the temperature dependent experiment performed with the VSM to explore the orientation of the magnetic particles in a magnetic field and determine their dynamic behavior, melt viscosity, and the rotation of the magnetic moment in a strontium ferrite-PA12 composite “below the matrix melting temperature” and “above the matrix melting temperature”. Furthermore, biaxial VSM was used to measure the magnetic anisotropy of the samples and anisotropy depends on the field annealing process through induced shape anisotropy contributions originating from agglomerates. Magnetic anisotropy increases with the increase of the field annealing time of the composites. For 22 kOe field-anneals, the measured magnetic anisotropy is larger than an individual particle’s effective anisotropy (Keff), providing evidence for significant agglomeration along the anneal field direction. This conclusion is supported by SEM analysis showing good particle alignment and significant chaining. We also discussed the 3D printed sample's magnetic anisotropy by VSM and in addition, a Torque magnetometer (TM) has used to measure the anisotropy of the 3D printed sample to do the comparative analysis of TM and VSM results. These magnetic characterization efforts were complemented with SEM, EDS, FTIR, XRD, TGA, and DSC studies for morphological, chemical, structural, and thermal properties analysis.
magnetic anisotropy, 3D printing, bonded permanent magnet, magnetic texture
Ahmed, T. N. (2023). Magnetic and morphological characterization of SrFe12O19/PA12 composites: Hard-magnetic filament for Magnetic Field Assisted Additive Manufacturing (MFAAM) (Unpublished dissertation). Texas State University, San Marcos, Texas.