Laser powder bed fusion of Fe-6.5 wt %Si soft magnetic alloys: the effect of in-situ alloying and powder morphology

Biyiklioglu, Mumin 2026. Laser powder bed fusion of Fe-6.5 wt %Si soft magnetic alloys: the effect of in-situ alloying and powder morphology. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Fe-6.5 wt %Si alloys offer superior soft magnetic properties but suffer from extreme brittleness, which severely limits fabrication via conventional methods. This thesis investigates manufacturing these alloys via laser powder bed fusion (LPBF), addressing whether in-situ alloying from elemental powder blends is viable, how powder morphology governs process behaviour and magnetic performance, and whether LPBF can competes with powder metallurgy. Three feedstocks were characterised and processed: commercial powder, mechanically alloyed powder, and as-blended elemental Fe-Si powders. Spark plasma sintering at 950 °C provided a solid-state baseline, achieving relative densities of 97.1–98.7% and saturation magnetisation values of 1.77–1.81 T. Elevated coercivity (649–1058 A/m) confirmed that this behaviour is intrinsic to the powder systems rather than process-induced. LPBF of commercial powder established an optimal energy density window of 100–150 J/mm³, yielding relative densities exceeding 95%, saturation magnetisation up to 1.88 T, and coercivity of 761 A/m at 200 W.Mechanically alloyed powder introduced severe short-feed and denudation effects. In-situ alloying from elemental blends was successfully demonstrated and chemically homogeneous Fe-Si distribution with no macro-segregation confirmed by EDS. Saturation magnetisation achieved up to 1.79 T at 200 W with a linear correlation established between relative density and magnetic saturation. A validated multi-physics model confirmed Marangoni-driven convection achieves complete homogenisation within the microsecond-scale melt pool, with simulated track widths agreeing with experiment to within 4.3%. ANOVA on ranks across 72 samples identified powder type as the dominant densification factor and laser power as the primary controllable parameter for saturation magnetisation, coercivity, and remanence. No process parameter influenced permeability, establishing post-process heat treatment at 1100 °C through stress relief, and grain coarsening as the only reliable improvement strategy. This research validates in-situ alloying as a cost-effective route for Fe-6.5 wt %Si components and lays a foundation for future multi-material additive manufacturing of electromagnetic devices.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Additive Manufacturing 2. Laser powder Bed Fusion 3. Soft Magnetic Materials 4. In-Situ Alloying 5. Powder Morphology 6. Fe-Si Alloys
Date of First Compliant Deposit:	30 June 2026
Last Modified:	30 Jun 2026 10:18
URI:	https://orca.cardiff.ac.uk/id/eprint/187814

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