Al2O3 “self-coated” iron powder composites via mechanical milling

Abstract

Electrically insulated ferrous powders permit isotropic magnetic flux, lower core losses, and structural freedom for state-of-the-art electromagnetic (EM) core and device designs. Many current coating materials are limited by low melting temperatures, which leads to insufficient insulation of powders, resulting in metal-on-metal contact. Use of a high-temperature coating material, such as alumina, could alleviate these issues. In this work, iron powder was mechanically milled with alumina media, to yield plastically deformed, alumina-coated iron particles with improved magnetic saturation, elastic modulus, and hardness. Various milling times and media ball sizes are investigated to maintain particle size, insulate powders uniformly, and optimize properties after compaction and curing. We found that longer milling times yielded more dense powder coatings and lower magnetic saturation.