Development of methodology for surface analysis of soft magnetic composite powders

Abstract

Soft magnetic composites (SMCs) are designed for the sustainable industrial production of uniform isotropic components with three-dimensional magnetic properties. The nanocoating covering the surface of water-atomized iron powder is the paramount feature of SMC technology that gives the material the high resistivity needed for minimizing the negative effects of eddy currents. An analysis of its initial state/composition on a micro level and any changes during further compaction and heat treatment is thus of great importance. Therefore, a method for the evaluation of composition and thickness of such insulating coatings was developed in this study. High resolution imaging combined with surface analytical and depth profiling techniques (high resolution scanning electron microscopy (HR SEM) with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy) were used. Analyses were performed on commercially available SMC powder grades having a phosphate-based coating. Depth profiling was carried out by ion etching and X-ray photoelectron spectroscopy analysis. The analyses revealed the presence of oxygen (O1s), iron (Fe2p), and phosphorous (P2p), indicating these elements as the main components of the insulating coating. Two approaches for the evaluation of the coating thickness were tested based on the relationship between the normalized intensity of the iron metal peak and etch depth where the phosphorus and oxygen intensities reach half the difference of their maximum and minimum values. Results indicate that the thickness of the coating extends to the~30 nm depth into the surface. For HR SEM imaging, utilization of an InLens detector for secondary electron imaging and a low acceleration voltage (~5 kV) is recommended for HR SEM + energy dispersive X-ray spectroscopy analysis of coating morphology and composition.

Evolution of phosphate coatings during high-temperature annealing and its influence on the Fe and FeSiAl soft magnetic composites

“…5b and c. The Fe2p peak can be fitted with three components including Fe 2+ , Fe 3+ and Fe. This is consistent with previous studies that ferric and ferrous irons have been observed in the Fe2p peak for the glassy iron phosphate [18,29]. The P2p peaks in Fig.…”

“…Among these coatings, phosphate has been widely used in the fabrication of the SMCs due to its simple preparation process, high electrical resistivity and strong adhesion to the powder surfaces [11][12][13]. A great amount of work has been carried out to study the microstructure and chemical composition [14][15][16][17][18] of the phosphate coating, as well as its optimized preparation procedures for improved properties of the SMCs [3,10].…”

An XPS investigation on the thermal stability of the insulating surface layer of soft magnetic composite powder

“…A wide range of materials have been utilized as coatings in the SMC concept, with phosphates being extensively preferred among other reasons thanks to their low conductivity, chemical durability, non‐toxicity and recyclability, good cohesion to the substrate material and inexpensive synthesis derived from standardized metal conversion methods . In our previous studies, a methodology for characterizing SMC powders based on iron phosphate coatings has been presented, followed by an investigation on the effect of temperature and air as annealing atmosphere on fully processed components . In the latter case, the complexity of the nature of the surface layer developed under treatment has been noted for different regions of the components, exhibiting the impact of the processing atmosphere.…”

“…Furthermore, an X‐MAX 20‐mm 2 detector (Oxford Instruments, High Wycombe, England) was utilized in this configuration for EDX chemical microanalysis, while a silicon standard was used for the calibration of peaks position and intensities. The conditions for achieving optimum microscopic imaging and chemical microanalysis results are described in our previous investigation . Surface sensitive chemical analysis was performed in a PHI 5500 XPS (PERKIN ELMER, Eden Praire, Minnesota, USA) equipped with a monochromatic AlK a (1486.6 eV) X‐ray source.…”

Analysis of the Fracture Surfaces of New Development Insulated Iron Powder Compounds

“…In addition, the material could be easily shaped into 3D structures in order to fully take advantage of the material's isotropic nature [1][2][3][4][5].…”