Correlation of B2 super-lattice ordering with soft magnetic and mechanical properties of nanocrystalline FeCoNbB HITPERM alloys

Abstract

The degree of superlattice ordering (S), which may vary from zero (complete disorder) to one (fully ordered) is known to influence the magnetic and other physical properties of Fe-based nanocrystalline alloys. The direct correlation of S with physical properties of these alloys is not yet established. In the present work, we report on the correlation of the atomic order parameter (S) of bcc-FeCo phase, as calculated by anomalous diffraction measurements with the soft magnetic and mechanical properties of (Fe1-xCox)81Nb7B12 (x = 0.25, 0.33, 0.5, 0.66, 0.75) HITPERM alloys. The measured soft magnetic properties such as coercivity and saturation magnetization are found to have better correlation with the degree of atomic order than that of the crystalline volume fraction for the studied partially nanocrystalline alloys. Highest saturation magnetization (147 A.m2/kg) and lowest coercivity (18 A m−1) is recorded for the alloy (x = 0.66) with maximum degree of atomic order (S ∼ 0.82). Ductility test shows better resistance against the embrittlement for the atomically ordered alloys as compared to disordered ones. Micro-hardness values are also high for atomically ordered alloys. The study suggests that apart from grain size, nanocrystalline fraction etc, the degree of atomic order is also an important structural parameter for tailoring the physical properties of such alloys for technological applications.