Magnetic hardening of Cr-/W-added NdDyFeCoB sintered magnets

The addition of 2 at% Cr or W into a sintered (Nd,Dy)-(Fe,Co)-B alloy is very effective in improving room temperature coercivity and thermal stability. The W-containing alloy showed twice the coercivity value to that of W-free alloy at temperatures higher than 100 degrees C. Both W and Cr alloying greatly improve the high temperature stability. There exists a WFeB precipitate phase in the W-containing alloy. The WFeB phase is platelet with its long axis parallel to c-axis of the 2-14-1 phase. The domain wall pinning at the precipitate phase, as evidenced by the Lorentz microscopy, is the reason of enhanced coercivity of this alloy, particularly at high temperatures.