Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding

Abstract

The plasma assisted ball milling technology is employed for the preparation of hard magnetic Sm2Fe17NX magnetic powders for the first time. Using conventional high-energy ball milling, Sm2Fe17 alloy powders can only be prepared from Sm2Fe17 alloy precursor but not from Sm and Fe metal precursor. However, by the plasma-assisted ball milling, Sm2Fe17 alloy powders with very fine grains can be directly obtained from the mixture of pure Sm and pure Fe fragments. It is also found that the Sm2Fe17 alloy has been partially nitrided by plasma assisted ball milling under nitrogen atmosphere. The precipitation of soft magnetic α-Fe phase and the oxidation of Sm2Fe17 particles can also be effectively inhibited by the plasma during milling. In addition, the nitriding effect of Nd-Fe alloy powders prepared by plasma-assisted ball milling is better than those prepared by conventional high-energy ball milling during the subsequent nitrding process, since the plasma field can increase the initial free energy of Sm2Fe17 powder and reduce its difference with the energy barrier. The present wok indicates that the nitriding efficiency of Sm2Fe17 alloy can be greatly improved by adding plasma field during the powdering.