Microstructure refinement and magnetic property enhancement for nanocomposite Nd2Fe14B/α-Fe alloys by Co and Zr additions

The effects of Co and Zr additions on the microstructure, magnetic properties and crystallization behaviour of nanocomposite Nd2Fe14B/α-Fe magnets have been investigated. It was found that Co addition decreases the precipitation temperature of crystalline phases, improves the Curie temperature of magnetic phases and clearly increases the remanence. On further Zr addition, the crystallization behaviour changes from a two-step to a single-step process, and the grains are markedly refined, especially for the α-Fe phase. The unit cell and the Curie temperature of the Nd2Fe14B phase decrease, suggesting that Zr atoms partly enter the Nd2Fe14B structure and occupy the rare earth sites. Hence, the volume fraction of hard magnetic phase increases, the intrinsic coercivity increases from 445 kA/m for the Zr-free sample to 687 kA/m for the Zr-doped sample and a maximum energy product of 129 kJ/m3 is achieved for Nd9.5Fe76Co5Zr3B6.5 alloy.