The influence of zirconium on Sm(Co, Fe, Cu, Zr) 7.2 alloys for permanent magnets II: Composition and lattice constants of the phases in heat-treated materials

Abstract

Specimens of composition Sm(Co 0.69Fe 0.22Cu 0.06Zr 0.03) 7.2 were submitted to either long annealings at 1160−850 °C or heat treatments similar to those applied to magnetic materials. The composition and lattice constants of the phases in the specimens were determined by electron-probe analysis and X-ray diffraction. Under equilibrium conditions, a mixture of 2:17 R, 2:17 H, 2:7 is stable at 1160−1000 °C. At 850 °C, a mixture of 2:17 R, 2:7 R, 5:19 is found. Apart from these phases, a 1:3 phase is present in specimens treated like permanent magnetic alloys. Iron is mainly distributed in 2:17, copper replaces cobalt in 2:7, zirconium replaces samarium and induces the precipitation of phases of the series Sm n+1 Co 5 n − 1 , at the expense of 1:5. The higher the zirconium content, the lower the n of the phase precipitated. Zirconium also extends the high temperature existence range of 2:17 H. The decomposition of this phase during the 850 °C step may be related to the formation of the cell microstructure typical in permanent magnetic alloys.