Effect of heat treatment in air on surface composition of iron-phosphate based soft magnetic composite components

tSoft magnetic composite materials (SMC) manufactured by conventional powder metallurgical tech-niques for electromagnetic applications constitute individually encapsulated ferromagnetic powderparticles with an insulating surface layer, bonded together into 3D finished structures. The produc-tion procedure includes compaction of the SMC base powder mixed with a lubricant substance and apost-annealing treatment that aims to relieve the stresses induced in the component during pressing.In the present study, the effect of the heat treatment process to the nature of the insulating layer wasinvestigated under different temperature regimes using analytical techniques. Its surface chemistry wasdetermined based on the XPS depth profiling technique, and its morphology and structure were evaluatedusing HR-SEM and XRD. Differences between interior and exterior areas of the samples suggested thedevelopment of an oxide scale in the outer regions that prevents its further bulk oxidation at temperaturesabove 500◦C, while below that temperature incomplete de-lubrication takes place.