Effect of Chill Wheel Cooling on Magnetic Properties of Nd<sub>15</sub>Fe<sub>77</sub>B<sub>8</sub> Alloy Powders Produced by Melt Spinning Method

Abstract

Abstract:In this study, effect of wheel cooling on magnetic properties of Nd 15 Fe 77 B 8 alloy powders produced by melt spinning method has been investigated. The present method includes the cooling of the copper wheel by externally contacting a coolant block which is cooled by internally circulating freon gas. Within this framework, the effect of wheel temperature on the microstructure and magnetic properties of Nd 15 Fe 77 B 8 powders have been investigated. The temperatures of cooling block and melt spinning wheel were measured as -15°C and -5°C, before experimental run, separately. Produced powders exhibited different morphologies depending on the powder sizes. The smallest size of powders was formed as spherical, ligamental and fiber-like morphologies. As powders get larger, the amount of spherical, ligamental and fiber-like shaped powders decreased and the length of the fibers declined. The microstructural cell sizes for 5 µm and 48 µm size powders were measured as 0.22 µm and 1.23 µm, respectively. The cooling rates of 4 µm, 28 µm and 52 µm sized powders were measured as 5.95 x 10 6 K/s, 0.85 x 10 6 K/s and 0.45 x 10 6 K/s, respectively. The Curie temperature of produced powders was 321.5°C. The coercivity value of melt-spun powders was obtained as 2.842 kOe.