Development of coercivity in Sm2Fe17(N,C)x magnets by mechanical alloying, solid–gas reaction, and pressure-assisted zinc bonding

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Abstract
Highly coercive isotropic Sm2Fe17Nx and Sm2Fe17Cy powders were prepared by a mechanical alloying of elemental Fe and Sm, a heat treatment in vacuum at 700–800 °C to form microcrystalline Sm2Fe17, and, finally, a solid–gas reaction in N2 and C2H2 atmosphere, respectively, at 450–500 °C to introduce nitrogen and carbon, respectively, on interstitial sites. The solid–gas reaction parameters, such as temperature and time as well as, in the case of carbides, the C2H2 partial pressure, are very critical with respect to dynamical decomposition of the Sm2Fe17 phase during reaction progress. Optimum parameters result in a coercivity of up to 25.6 kA/cm (32.2 kOe) and 18.5 kA/cm (23.2 kOe) for the nitride and carbide, respectively. Zinc bonding of such powders assisted by a uniaxial pressure of 200–300 MPa at a temperature of 425–450 °C leads to further substantial coercivity enhancement. The room‐temperature coercivity of Zn‐bonded Sm2Fe17Nx magnets reached 34.7 kA/cm (43.6 kOe), which represents an increase by about 50% referred to the starting powder value. The assistance of Zn bonding by pressure is required for the coercivity enhancement in such microcrystalline material.