Segregation of W in Nd-Fe-B magnets and its effects on coercivity

The coercivity of sintered Nd/sub 22/Fe/sub 71/B/sub 7/ magnets with the combined addition of Al and W was investigated to study the role of additive elements in improving the coercivity in the NdFeB system. It was found that the coercivity could be greatly enhanced by the Al and W combined addition. Microstructural studies show that the alloying element W would preferentially segregate on the surface region of the main phase grain when added into the magnets together with Al, leading to a significant enhancement of coercivity. Further, thermodynamic analysis reveals that the segregation of W could be attributed to inhomogeneous nucleating on the surface region of the main phase grains during cooling.