Effect of Zr substitution on microstructure and magnetic properties of YDy-based R_2Fe_(14)B magnets (R=Y+Dy+Nd)

摘要

The effect of Zr substitution on the microstructure and magnetic properties in [Nd_(0.5)(YDy)_(0.25)]_(2.2-x)Zr_xCo_(1.5)Fe_(12.5)B (x=0-0.7) ribbons melt spun at a wheel speed of 10 m/s has been systematically studied. For as-spun Zr-free ribbon, a coercivity H_(cj) of 15.5 kOe is obtained but the demagnetization curve exhibits a large shoulder, resulting in a very low maximum energy product (BH)_(max)(3 MGOe). With increasing Zr content (x), H_(cj) first decreases and then increases. When x=0.4, both H_(cj) and (BH)_(max) reach their optimized values of 10.6 kOe and 9.6 MGOe, respectively. The H_(cj) and (BH)_(max) for the sample at 200℃ are 5 kOe and 4.3. MGOe, respectively. Transmission electron microscopy characterizations show that the average grain size is 200, 65, and 50 nm for x=0, 0.4, and 0.7, respectively, indicating that the substitution of Zr can effectively inhibit grain growth. However, an excessive substitution of Zr results in the appearance of the 2:17 phase and thus the reduction of magnetic properties.