Effects of alloy composition and/or casting method on the amount Fe-precipitation in NdFeB alloys

According to the ternary Nd-Fe-B phase diagram, Fe-precipitation during the solidification of NdFeB alloy is anticipated because the solidification trajectory passes through a region of iron stability. The presence of Fe-precipitates not only causes difficulties in ingot crushing, pulverizing and fine milling but also lowers the magnetic properties and the corrosion resistance of NdFeB magnets. A dilute substitution of Nb, V or Ga for Fe has been known to improve the magnetic properties, in particular the intrinsic coercivity, the temperature coefficient of induction, and the corrosion resistance of NdFeB magnets. However, (the impact of these elements on) the precipitation of Fe during casting has never been discussed in the open literature.