Metallurgy and Magnetism: Metallurgy and Magnetism II
Program Organizers: Nicholas Jones, Naval Surface Warfare Center, Carderock Division; Paul Lambert, Naval Surface Warfare Center, Carderock Division
Thursday 8:00 AM
November 5, 2020
Room: Virtual Meeting Room 37
Location: MS&T Virtual
Session Chair: Paul Lambert, Naval Surface Warfare Center, Carderock Division; Nicholas Jones, Naval Surface Warfare Center, Carderock Division
8:00 AM
Comparative Studies on the Structure and Magnetic Properties of Mechanically Alloyed Fe40Co30Ni30 Medium-entropy Alloy in Argon and Ambient Atmospheres: Alex Paul1; Anuj Rathi1; Tanjore Jayaraman1; 1University of Michigan-Dearborn
We compare the structure and magnetic properties of mechanically alloyed Fe40Co30Ni30 medium-entropy alloy fabricated in argon (MA-Ar) and ambient (MA-Air) atmospheres. Irrespective of the atmosphere, the powders were micron-sized, constituting the nanocrystalline γ phase. The saturation magnetization (MS) of MA-Air was less than the MS of MA-Ar by a modest ~6%. The remanent magnetization (MR) and intrinsic coercivity (HCI) of MA-Air were higher than MA-Ar by ~19% and ~28%, respectively. At below-ambient temperatures, both MA-Ar and MA-Air exhibit similar behavior, i.e., MS, and HCI increased with a decrease in temperature. The thermomagnetic behavior of MA-Ar and MA-Air indicated the phase transformation γ α (Fe) + γ (Fe deplete) at above-ambient temperatures, between ~725 K and ~800 K. The Range of Value Method utility function analyses assigned MA-Air the highest utility value, among the as-prepared and thermally-treated Fe40Co30Ni30 alloy powders, suitable as a ferromagnetic precursor to fabricate semi-hard magnets.
8:20 AM
Improvement of the Magnetic Characteristics of Materials Due to the Formation of Unidirectional Boundaries of Ferrite during Processing in SHS Conditions: Borys Sereda1; Dmytro Sereda1; Vitalyy Volokh1; 1Dneprovsky State Technical University
To improve the magnetic characteristics of armco-iron, such as magnetic permeability and coercive force, samples were processed in conditions of self-propagating high-temperature synthesis. Heating was carried out to a temperature of 900 ° C, followed by isothermal holding and cooling at various speeds. The study of the microstructure of samples with a carbon content of up to 0.015% showed that grain boundaries are formed, which are divided into three unidirectional sections. Areas are established where both ends of the boundary enter triple joints with opposite angles exceeding 170 or quadruple joints are observed. Due to the non-stationary stage of the SHS process, a fine-grained structure is formed, which leads to an increase in the coercive force from 0.97 A / cm to 1.65 A / cm and, accordingly, to an increase in hardness from 95 to 157 HB.
8:40 AM
Development of FeCo/MnZn Ferrite Composite by Field Assisted Sintering Technique: Bowen Dong1; Gabriel Santillan2; Matthew Willard1; 1Case Western Reserve University; 2Powdermet Inc.
FeCo alloys have great soft-magnetic properties, but small resistivity, which leads to eddy current losses. FeCo/MnZn ferrite composite with superexchange insulating matrix to limit the eddy current path length should be able to diminish the eddy current loss. In this study, we developed bulk composite using sol-gel synthesized core-shell structured FeCo/MnZn ferrite powders consolidated using field assisted sintering. Relative density ≥ 95 % were achieved. Using optical microscopy and scanning electron microscopy, it was found that ‘brick-and-mortar’ insulating matrix structure had been successfully achieved when the MnZn ferrite content ≥ 11.56 wt.% in the core-shell powder. Hysteresis measurements using vibrating sample magnetometry indicates a saturation magnetization of 181 Am2/kg (flux density of 1.7 T) and coercivity of 1516 A/m in compacted samples of FeCo/MnZn ferrite (11.56 wt.%) powder.
9:00 AM
Exchange Coupled Ferromagnetism in Nanochessboards Obtained By Eutectoid Decomposition in the Co-Pt and Fe-Pt Systems: Adrian Savovici1; Eric Vetter2; William Soffa1; Jerrold Floro1; 1University of Virginia; 2NCSU
The nanochessboard is a fascinating microstructure in which to investigate exchange-coupled ferromagnetism. In Co-Pt, cooling through the eutectoid, A1 → L10+L12 , produces a quasi-periodic tiling of L10 nanorods coherently embedded in an L12 matrix. Both ordered product phases are ferromagnetic, where L10 (L12) has large (small) magnetocrystalline anisotropy. First order reversal curve analysis shows that exchange-coupling evolves from partial to complete as the period is reduced to the critical lengthscale. The Fe-Pt system offers distinct advantages, since there will be higher magnetic moment in the soft phase and larger anisotropy in the hard phase, vis-à-vis Co-Pt. However, the chessboard has not been previously observed in this system, and we will show initial results on eutectoid decomposition in the two-phase region. Micromagnetic simulations are also being carried out to examine the effects of increased magnetization and magnetocrystalline anisotropy. Support of the National Science Foundation through grant DMR-1709914 is gratefully acknowledged.
9:20 AM
Magnetic Performance of Gas-atomized Maraging Steel Powders: Ganesh Varma Thotakura1; Ramasis Goswami2; Tanjore Jayaraman1; 1University of Michigan-Dearborn; 2Naval Research Laboratory
Maraging steels are traditional ultra-high-strength structural alloys prominent in hydrospace and aerospace applications. We evaluated the magnetic performance and properties of gas-atomized maraging steel powder, over a range of temperatures, and compared with commercial semi-hard magnetic alloys. The magnetic properties of the powders were characterized by vibrating sample magnetometry, while the structure by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The powders predominantly comprised martensite along with traces of retained-austenite and intermetallic compounds. The powders exhibited the following magnetic behavior at ambient temperature: magnetic saturation (Ms) ~176 Am2/kg, magnetic remanence (Mr) ~1 Am2/kg, coercivity (Hc) ~3 kA/m, and magnetic anisotropy (K1) ~1.8 x 106 J/m3. The Ms, K1, Hc, and Mr increased at sub-ambient temperatures. The magnetic moment per atom (µh) of the powder was estimated to be ~1.93 µB. With the increase in thermal-treatment temperature, the MS and Hc increased and decreased, respectively, marginally.
9:40 AM
The Influence of the Microstructure Obtained After Processing in SHS Conditions on the Magnetic Characteristics of Steels: Borys Sereda1; Dmytro Sereda1; Vitalyy Volokh1; Vladimir Sukhomlyn1; Irina Kruglyak1; 1Dneprovsky State Technical University
Metallographic studies were carried out to establish the influence of the microstructure after cold deformation and subsequent processing under conditions of self-propagating high-temperature synthesis (SHS) on the magnetic characteristics of steels, such as coercive force, grain size, and the relative number of unidirectional boundaries. After processing the cold-deformed material under SHS conditions, the grain size decreases from 10.3 μm to 5.22 μm, and the relative number of unidirectional boundaries increased from 23.7% to 37.2%. The fine-fiber structure is the result of elongation and deformation of grains during material drawing, which is confirmed by the high value of the coercive force of 9.4 A/cm. The non-stationary stage of the process of self-propagating high-temperature synthesis, leads to grain refinement and an increase in magnetic permeability. The value of coercive force allows you to control changes in the structure of the wire at all stages of its metallurgical production.