Effect of Zr additions on the microstructural and magnetic properties of NdFeB based magnets

The microstructure of a sintered magnet made from Zr-containing NdFeB material was investigated using optical microscopy and scanning and transmission electron microscopy. The authors observed three phases in addition to those found in the ternary alloy. Two of these phases were Zr-rich, one having a lamellar structure and containing some iron and neodymium, and a second Zr-rich phase containing a small amount of iron. A substantial amount of Zr was found in the NdFe₄B₄ phase with Zr occupying some of the iron sites. A third phase took the form of small coherent precipitates within grains of the hard magnetic phase and was shown to be richer in Zr than the surrounding matrix. Magnetic measurements show an enhanced coercivity over the ternary alloy, which is attributed to the presence of coherent precipitates within the hard magnetic phase.