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

The coercivity of sintered Nd-22 Fe71B7 magnets with the combined addition of Al and W was investigated to study the role of additive elements in impr oving the coercivity in the NdFeB system. It was found that the coercivity could be greatly enhanced by the Al and W combined addition. Microstructura l studies show that the alloying element W would preferentially segregate o n the surface region of the main phase grain when added into the magnets to gether with Al, leading to a significant enhancement of coercivity. Further , thermodynamic analysis reveals that the segregation of W could be attribu ted to inhomogeneous nucleating on the surface region of the main phase gra ins during cooling.