Nanostructure and compositional segregation of soft magnetic FeNi-based nanocomposites with multiple nanocrystalline phases

• Published in: Journal of Materials Research
• Main Authors: Ohodnicki, P, Kautz, E J, Devaraj, A, Y. Yu, Aronhime, N, Krimer, Y, McHenry, M E, Leary, A
• Format: Web Resource
• Language: English
• Published: Hampton NASA/Langley Research Center 04.02.2021
• Subjects: Alloy systems; Alloys; Annealing; Body centered cubic lattice; Crystallization; Devitrification; Face centered cubic lattice; High resolution electron microscopy; Intermetallic compounds; Iron; Nanoalloys; Nanocomposites; Nanocrystals; Nucleation; Orientation relationships; Partitioning; Phases; Rapid solidification

Soft magnetic metal amorphous nanocomposite alloys are produced through rapid solidification and thermal annealing yielding nanocrystals embedded within an amorphous precursor. Similar free energies in Co-rich and FeNi-based alloy systems result in multiple nanocrystalline phases being formed during devitrification. Studies of multi-phase crystallization processes have been reported for Co-rich alloys but relatively few have investigated FeNi-based systems. A detailed characterization of compositional partitioning and microstructure of an optimally annealed FeNi-based MANC (Fe70Ni30)80Nb4Si2B14 alloy is presented through complementary high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). HRTEM demonstrates orientation relationships between FCC and BCC nanocrystals, suggesting heterogeneous nucleation of nanocrystals in the amorphous matrix or a cooperative mechanism of nucleation between BCC and FCC nanocrystallites. APT results show evidence for (i) the segregation of Fe and Ni between nanocrystals of different phases, (ii) B partitioning to the amorphous phase, and (iii) an Nb-enriched shell surrounding nanocrystals.