Application of Cold Sintering for Fabrication of Soft Magnetic Composites

Abstract

Three-dimensional flux motors, employing high-strength soft magnetic composites made from powdered metals, are considered a promising alternative to current state-of-the-art motors. In this study, we demonstrate that cold sintering of iron particles coated with an insulating hydrated oxalate coating led to the creation of a soft magnetic composite with approximately 55 MPa of transverse rupture strength when compacted at 100ºC. Upon subsequent heat treatment up to 700ºC, the strength significantly rose to almost 219 MPa, which is more than ten times that of conventional powdered metal compacts. During the heat treatment process, the oxalate further undergoes transformation into insulating iron/copper oxide coating around the iron particles. We systematically examined this chemical transformation using diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron dispersive x-ray spectroscopy. Our findings from AC and DC magnetic measurements of the cold-sintered toroid, in relation to heat treatment temperature, demonstrate an increase in DC permeability with rising heat treatment temperatures. Additionally, our analysis of AC core loss data revealed that hysteresis power losses dominate the performance at lower heat treatment temperatures (< 300°C), beyond which dynamic core losses showed significant escalation.

Keywords: - Cold sintering, Soft magnetic composite, Mechanical strength, Core loss contributions