Microstructure of aged (Co,Cu,Fe)7Sm magnets

Abstract
The microstructure of (Co,Cu,Fe)7Sm magnets has been characterized at various states of aging by transmission electron microscopy. At peak magnet properties, the magnet consists of cells of 17 : 2 phase about 500 Å in diameter, separated by a thin continuous fully coherent 5 : 1 boundary phase. This structure evolved by precipitation of ordered 17 : 2 particles from a disordered 5 : 1 matrix, and coarsens with aging until full coherence is lost and the cellular structure breaks up. The overaged alloy consists of semicoherent 5 : 1 particles in a 17 : 2 matrix, with a single set of interface dislocations accommodating the lattice mismatch. The effect of these various microstructural changes on domain‐wall pinning and coercivity is discussed.

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