Metallurgical behavior of Sm(Co,Fe,Cu,Zr)z alloys

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Abstract
A model, based on the Sm‐Co system between SmCo5 (1:5) and Sm2Co17 (2:17 R and 2:17 H), is proposed to describe the metallurgical behavior of Sm(Co,Fe,Cu,Zr)z alloys between 6.8<zz values; (2) Cu stabilizes the 1:5 phase relative to the 2:7 and 2:17 R phases at low temperatures; (3) low concentrations of Fe (≂5 a/o) stabilize the 2:17 R phase relative to the 1:5 phase and Co‐rich solid solutions in the presence of Cu; (4) high concentrations of Fe(>10 a/o) destabilize the 2:17 R phase due to Fe‐Fe pairs which preferentially occupy the dumbbell sites (6c in R3̄m); (5) Zr‐vacancy pairs stabilize the 2:17 R phase at high Fe concentrations by displacing Fe‐Fe pairs at the dumbbell sites; (6) high coercivity permanent magnets of the type Sm(Co,Fe,Cu,Zr)z with 6.8<z<8.5 have a partially disordered 2:17 R structure at the solutionizing temperature, and this structure is retained on quenching to room temperature. On isothermal aging, Cu is rejected from the 2:17 R phase by the formation of the Cu:rich 1‐5 boundary phase, and Zr is rejected by the formation of the Zr‐rich 2:17 H platelet phase.