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

• Published in: Materials science & engineering. B, Solid-state materials for advanced technology Vol. 189; pp. 90 - 99
• Main Authors: Oikonomou, C., Oro, R., Hryha, E., Nyborg, L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2014
• Subjects: Depth profiling; Heat treatment; Insulating surface coatings; Lubricants; Materials science; Metallurgical constituents; Morphology; Powder metallurgy (PM); Scale (corrosion); Soft magnetic composites (SMC); Three dimensional; X-ray photoelectron spectroscopy; X-ray photoelectron spectroscopy (XPS); Soft magnetic composites (SMC); Insulating surface coatings; Depth profiling; X-ray photoelectron spectroscopy (XPS); Powder metallurgy (PM)
• ISSN: 0921-5107; 1873-4944
• DOI: 10.1016/j.mseb.2014.08.003

•Surface morphological and chemical depth profiling analyses of SMC parts.•Effect of annealing at exterior/interior areas for different temperature regimes.•Difference in degree of oxidation/nature of bulk/coating with area and temperature.•Thermodynamic calculations/considerations on the thermal stability of the coating.•Incomplete delubrication and strong bulk oxidation of the samples under 500°C. Soft magnetic composite materials (SMC) manufactured by conventional powder metallurgical techniques for electromagnetic applications constitute individually encapsulated ferromagnetic powder particles with an insulating surface layer, bonded together into 3D finished structures. The production procedure includes compaction of the SMC base powder mixed with a lubricant substance and a post-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 was investigated under different temperature regimes using analytical techniques. Its surface chemistry was determined based on the XPS depth profiling technique, and its morphology and structure were evaluated using HR-SEM and XRD. Differences between interior and exterior areas of the samples suggested the development of an oxide scale in the outer regions that prevents its further bulk oxidation at temperatures above 500°C, while below that temperature incomplete de-lubrication takes place.