Investigation of the magnetic properties and fracture behavior of Nd-Fe-B alloy powders during high-energy ball milling

Abstract

In this work, Nd-Fe-B alloy powders are fabricated via high energy ball milling and their fracture behavior and magnetic properties are investigated at different milling times. The powder characteristics (particle shape, size, size distribution, and microstructure) and magnetic properties of the Nd-Fe-B alloys are systematically analyzed. The initial spherical Nd-Fe-B powder is cracked/crushed even after a short period of milling (30 s) due to the high impact energy generated during high energy ball milling. These randomly cracked polygonal-shaped powders are fragmented after 5 min of milling and converted to fine powders. Interestingly, the fine particles after milling for 5 min are conducive to agglomeration at longer milling times (20-60 min) and formed spherically-shaped agglomerated powder. Additionally, the sphericity of the powder increased to 92% by re-pulverization and agglomeration at 60 min. The milled powder shows the Nd2Fe14B phase, and the x-ray diffraction patterns exhibit peak broadening with increasing milling time, clearly confirming the powder refinement behavior by high energy ball milling. The magnetic properties of the milled powders are systematically investigated and their behavior is elucidated as a function of the milling time.