Microstructure characterization of ball milled Sm(CoCuFeZr) 2:17 powders

Abstract

The microstructure evolution and coercivity development in ball milled Sm(Co,Cu,Fe,Zr)z powders have been investigated by TEM, SEM, HRTEM, and VSM. The fully heat-treated Sm(Cobal,Fe0.1,Cu0.08,Zr0.03)7.5 and Sm(Cobal,Fe0.1,Cu0.08,Zr0.03)8.3 alloys were ball milled to powders with different ball milling rates and times. At a low ball milling rate, both the particle size and coercivity decrease slowly and monotonically with increasing milling time. Even after 48h milling, both powders with an average particle size of about 2μm still retain about 40%–50% of their initial coercivity. Both the cellular and lamellar structures are still observed in the two powders even after 48h milling, although crystal lattice distortion and defects are introduced into the cellular and lamellar structures in both powders. At a high milling rate, both the particle size and the coercivity drop sharply with milling time for both powders, and even 2min milling leads to the loss of 50% of the initial coercivity; the mean particle size was measured to be 5μm, whereas the initial cellular structure was significantly destroyed and highly strained. Further ball milling leads to sample oxidation and the formation of amorphous phase.