High intrinsic coercivities in iron-rare earth-carbon-boron alloys through the carbide or boro-carbide Fe14R2X (X=BxC1−x)

Abstract

In the phase Fe₁₄R₂X, where R is a lanthanide and X is either boron or carbon, or a mixture of the two, the extent of stability of the carbides and their miscibility with the borides is traced for the lighter rare‐earth metals. Like the borides, the carbides are magnetically hard, but unlike them, they do not normally crystallize from the melt, and this property is exploited to produce intrinsic coercivities above 12 kOe in cast materials without the added special processing step of sintering or melt spinning. The high coercivity is related to a cellular microstructure of Fe₁₄R₂X in which the cell size is approximately 1 μm. The cell structure, which originates in a peritectoidlike transformation from primary Fe₁₇R₂, is quite stable and does not change during prolonged annealing. The coercivity is sensitive to variations in composition.