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Description
Bonded magnets are functional composite materials consisting of a polymer matrix and magnetic filler particles. Their performance is closely linked to their internal structure, making suitable characterization methods essential. This work focuses on a methodological comparison between two materialographic approaches for bonded magnets: conventional scanning electron microscopy (SEM)-based analysis of polished cross sections and micro-computed tomography (micro-CT).
The investigated bonded magnets consist of a polylactic acid (PLA) polymer matrix containing Nd-Fe-B magnetic particles. SEM analysis of polished cross sections is a widely used approach for observing the microstructure of such composites. Its main advantages are relatively low cost, faster analysis, and high-resolution surface imaging. However, the method requires sample preparation, which may introduce artefacts. During conventional grinding and polishing, filler particles can be removed from the matrix, and pores may become filled or obscured by displaced material. Even with cross-section polishing, achieving a completely flat surface suitable for SEM observation can be time-consuming. In addition, SEM provides information from only one section at a time, making three-dimensional reconstruction difficult, time-intensive, and potentially inaccurate due to challenges in controlling the spacing between individual sections.
Micro-CT offers a different approach by enabling direct three-dimensional visualization of the bonded magnet structure without mechanical sample preparation. This allows porosity and internal features to be examined in the as-produced state. However, micro-CT is more expensive and time-consuming than SEM, and its usefulness depends on factors such as contrast and resolution.
The planned comparison will evaluate both methods with respect to contrast, resolution, filler concentration, porosity, and general suitability for bonded magnet characterization. The study aims to clarify the advantages and limitations of each method.