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

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<z<8.5 in the development of hard magnetic properties. The same phases are encountered in both the binary and multicomponent alloys, but the stability ranges of the 1:5 and 2:17 phases are altered by the additive elements. The following points are made: (1) Cu, and Fe in combination with Cu, extend the high temperature stability of the 2:17 R phase to lower z 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.