Phase equilibria of Sm-Fe-Ti-M (M = Cu, Ag) systems and wetting behavior of M-Sm alloys on SmFe₁₁Ti substrate

A SmFe_12-nX_n permanent magnet requires the formation of a suitable grain boundary phase in the microstructure. In this study, Cu and Ag were selected as the major components of the grain boundary phase, and phase equilibria involving the SmFe₁₁Ti phase were investigated. The wettability behavior of the molten grain boundary phase on SmFe₁₁Ti was studied based on this investigation. In the phase equilibria investigation for Fe–Ti–Sm–M (M = Cu, Ag), SmFe₁₁Ti equilibrated Cu-41 mol% Sm and Ag-44 mol% Sm at 1273 K in Cu and Ag systems, respectively. During study of the wetting behavior, molten Cu-41 mol% Sm alloy that equilibrates with SmFe₁₁Ti exhibited good wettability on the SmFe₁₁Ti substrate, with a final contact angle of 8° at 1133 K. The molten Ag-44 mol% Sm alloy that equilibrates with SmFe₁₁Ti also exhibited good wettability, with a final contact angle of less than 1° at 1273 K. Although the damage to the SmFe₁₁Ti substrate by Ag-44 mol% Sm alloy seemed smaller, the difference in the damage to the substrate could not be evaluated between Cu-41 mol% Sm alloy and Ag-44 mol% Sm alloy because the Ag-44 mol% alloy wetted the entire substrate and flowed down through the lateral side of the substrate.