Effect of Dy on the microstructural and magnetic properties of an Nd-Fe-B strip-cast alloy

This paper examines the effect of Dy on the microstructural and magnetic properties of an (Nd_32.57-x,Dy_x)Fe_bal.B _0.97 (wt%; x=4.89, 6.51, 8.14, 9.77) strip-cast alloy. The average interlamellar spacing is reduced, and the grain uniformity and (00l) grain alignment in the direction perpendicular to the plane of the strip-cast alloy are enhanced as the Dy content is increased. Furthermore, the formation of α-Fe is increasingly suppressed as the Dy content is increased. These microstructural changes can be explained by an increase in the effective cooling rate of the melted alloy, which is caused by an increase in the solidus temperature of the (Nd,Dy)₂Fe₁₄B phase resulting from the substitution of Dy with Nd. The appearance of DyNdO₃ precipitates in the grain boundaries also contributes to the grain refinement. Therefore, the improvement in the magnetic properties afforded by the addition of Dy depends on the large anisotropy field of Dy₂Fe₁₄B; it also depends on the grain refinement and alignment caused by the increased effective cooling rate and by the DyNdO₃ precipitates that form along the Nd-rich grain boundaries.