Development of high-coercivity state in high-energy and high-temperature Sm-Co-Fe-Cu-Zr magnets upon step cooling

摘要

The work compares the peculiarities of the high-coercivity state formation in the Sm-Co-Fe-Cu-Zr high-temperature and high-energy permanent magnets (HTPM and HEPM) in the course of the heat treatment with the stepwise decreasing temperature from 830 to 400 degrees C. Two types of magnets with varying Fe concentration, i.e., Sm(Co0.88-xFexCu0.09Zr0.03)(7) with x = 0-0.12 (the HTPM5) and SM(Co0.91-xFexCu0.06Zr0.03)(7.5) with x = 0.24-0.33 (the HEPM5) were studied at different temperatures of heat treatment for phase formation by x-ray diffraction followed by magnetic property measurements. Microstructure characterization was performed using transmission electron microscopy, whereas the three-dimensional elemental distribution at near-atomic scale was obtained using atom probe tomography. In HEPM5, the main increase in coercivity and relaxation of stresses accompanied by intensive enrichment of the 1:5 phase in Cu are observed at high temperatures (T approximate to 700 degrees C). In HTPM5, the coercivity monotonously increases in the entire temperature range of the slow cooling from 700 to 400 degrees C at a rate of 0.5 degrees C/s. At the temperature close to the Curie temperature (similar to 550 degrees C) of the Sm(Co,Cu)(5)-type phase, the anomaly of the coercivity increment has been observed. The interphase stresses grow and the elemental redistribution appears to be accelerated simultaneously. The non-uniform Cu distribution in the 1:5 phase can be described by the formation of Cu-rich interlayers at the interface of the Sm(Co,Cu)(5) and Sm-2(Co,Fe)(17)-type phases. (C) 2019 Elsevier B.V. All rights reserved.