Effect of interfacial stress on microchemistry and coercivity in 2:17-type SmCo sintered magnets

Abstract

The coercivity of 2:17-type SmCo magnets is mainly determined by the gradient distribution of Cu element within the cell boundary phase, and the gradient of Cu distribution increases with aging time, together with coercivity. However, the fundamental origin of such Cu gradient distribution is not clear. In this work, the element redistribution and interfacial stress change during the aging process were simultaneously analyzed by employing typical Sm(CobalFe0.16Cu0.08Zr0.03)7.6 magnets with and without slow cooling. The increased atomic diffusion after slow cooling leads to a narrow width and large Cu distribution gradient of 1:5H phase, contributing to a high coercivity. Meanwhile, the lattice mismatch at the 1:5H/2:17R interface along 〈1¯010〉2:17R direction was enhanced in the magnet with slow cooling, giving rise to a large interfacial stress. Such interfacial stress was found, via physical chemistry analysis, to contribute to the gradient of Cu distribution in the 1:5H phase. The combined analysis of transmission electron microscopy, geometric phase analyses, and micromagnetic simulations reveal the presence of the interfacial stress together with a large concentration and gradient of Cu distribution in the 1:5H phase can improve the coercivity. These findings provide new considerations for the design of high-performance 2:17-type SmCo magnets.