Effects of partial substitution of V and Ti for Fe on nitrogenation rate and magnetic properties of Sm 2Fe 17N x anisotropic coarse powders

Abstract

Sm 2(Fe 1− y V y ) 17N x and Sm 2(Fe 1− y Ti y ) 17N x ( y=0.05 and 0.015) coarse powders were synthesized by crushing mother alloy ingots into 32–74 μm particle size and subsequent nitrogenation at 598–748 K in a flowing mixed gas of H 2–NH 3 (60:40, v/v). The effects of partial substitution of V and Ti for Fe on the nitrogenation rate and the magnetic properties of the Sm 2Fe 17N x hard magnetic material were investigated. The partial substitution of V and Ti was quite effective for accelerating nitrogenation. The Sm 2(Fe 0.95V 0.05) 17N x and Sm 2(Fe 0.95Ti 0.05) 17N x powders showed poor magnetic properties because of rapid nitrogenation due to a high affinity of V and Ti for nitrogen. When the V and Ti content was reduced to y=0.015 from y=0.05, the magnetic properties were significantly improved. The highest maximum energy product, 51.1 kJ/m 3, was obtained for the Sm 2(Fe 0.985Ti 0.015) 17N 4.7 powder among the nitrogenated Sm 2(Fe 1− y V y ) 17N x and Sm 2(Fe 1− y Ti y ) 17N x ( y=0.05 and 0.015) powders. These nitrogenated powders synthesized in this study also possessed a satisfactory magnetic anisotropy. In order to homogenize the nitrogen distribution in the powder, the Sm 2(Fe 0.985Ti 0.015) 17N 4.7 powder were annealed in Ar. The nitrogen content and the peaks from the 2-17 crystalline phase in the X-ray diffraction pattern of the annealed sample were reduced and shifted to a higher angle side, respectively, as compared to the sample before annealing. The annealing was found to be effective for enhancing the magnetic properties such as coercivity and rectangularity of the hysteresis loop. In this study, the (BH) max value, 82.1 kJ/m 3, was obtained for the annealed Sm 2(Fe 0.985Ti 0.015) 17N 4.2 powder, which is significantly large as compared to the powder before annealing.