Metallurgy and Magnetism: Metallurgy and Magnetism I
Program Organizers: Nicholas Jones, Naval Surface Warfare Center, Carderock Division; Paul Lambert, Naval Surface Warfare Center, Carderock Division
Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 37
Location: MS&T Virtual
Session Chair: Nicholas Jones, Naval Surface Warfare Center, Carderock Division; Paul Lambert, Naval Surface Warfare Center, Carderock Division
2:00 PM
Introductory Comments: Metallurgy and Magnetism: Nicholas Jones1; 1Naval Surface Warfare Center, Carderock Division
Introductory Comments
2:05 PM
Processing of Fe-Co Alloys: Past and Present: Zafer Turgut1; Alex Leary2; John Horwath1; Gregory Kozlowski3; 1AFRL/RQQM; 2NASA Glenn Research Center; 3Wright State University
Because it contains cobalt, Fe-Co is an expensive alloy and its magnetocrystalline anisotropy is higher than other soft magnetic materials. However, Fe-Co is the material of choice for many aerospace applications due to its unmatched saturation flux density, mechanical strength and temperature performance. There has been a little change in terms of how these alloys are processed into thin laminations over the years and only a handful of new compositions have emerged since its discovery. New aerospace initiatives seek several megawatts of on-board power generation and conversion, and require Fe-Co in the forms of even thinner laminations beyond what is possible by cold rolling and grain refined bulk forms as rotors for electromachines. This work reports our efforts of 1) powder metallurgy (PM) processing of bulk Fe-Co alloys with improved mechanical performance and 2) melt spinning+cold rolling processing to arrive at thinner laminations for improved frequency performance.
2:25 PM
The Effect of Deformation of Low Alloy Steels Used in Metallurgy on Their Magnetic Characteristics: Borys Sereda1; Dmytro Sereda1; Vitalyy Volokh1; Vladimir Sukhomlyn1; 1Dneprovsky State Technical University
As a result of studies of steel samples used in metallurgy during uniaxial tension of flat samples, the nature of the growth of the coercive force from the applied stresses was established during the transition of the metal from the elastic zone to the elastoplastic. The coercive force was determined on a KPM-S semi-automatic coercimeter in the central part of the sample. So for steel with 0.17% C, the value of the coercive force varied from 2.9 to 7.8 A/cm with an applied load of up to 500 MPa. The dependences of the coercive force on stress are obtained for materials with a C content of 0.17 to 0.9%. In the course of the studies, it was found that the coercive force in the zone of elastic deformation varies by 9-11%. The obtained studies on the characteristics of magnetism make it possible to assess the technical condition of metallurgical equipment.
2:45 PM
Microstructural Development and Mechanical Property Changes Due to Temper Embrittlement in HY-80 Submarine Steel: Charles D'Ambra1; Jason Schibler1; Michele Manuel1; Thomas Krause2; Aroba Saleem1; 1University of Florida, Department of Materials Science and Engineering; 2Royal Military College of Canada
HY-80 is a low-alloy, low-carbon steel used primarily in submarines for its high strength and toughness. HY-80 is susceptible to temper embrittlement caused by the migration of impurity elements and carbides towards the grain boundaries when held between the embrittling range of 370 to 600 ºC. There is currently no widespread non-destructive method for testing early stages of temper embrittlement of HY-80 steel. The purpose of this paper is to analyze the microstructural development and changes in mechanical properties to determine their relation to magnetic property variations. Five samples of HY-80 were heat treated at 525 °C for different holding times to induce varying degree of temper embrittlement. These samples were then characterized by scanning electron microscope (SEM), and Vickers microhardness tests. It was observed that hardness changed with holding time, and these changes were attributed to change in the carbide precipitate density within the matrix due to temper embrittlement.
3:05 PM
Effects of Steel Sensitization on Magnetic Properties Measured through MOKE Magnetometry: Nicholas Jones1; Olaf van 't Erve2; Emily Guzas3; Matthew Roberts1; 1Naval Surface Warfare Center, Carderock Division; 2Naval Research Laboratory; 3Naval Undersea Warfare Center, Division Newport
Magneto-Optical Kerr Effect (MOKE) magnetometry has been used to non-destructively measure the change in magnetic properties of stainless steel samples as a result of welding. While welding is used to join and repair steels, the heat input may cause undesirable changes in the base metal. Of particular interest is the precipitation or dissolution of carbide precipitates, resulting in sensitization or desensitization of the stainless steels, respectively, along with potential changes in the magnetic properties of the steel. While the state of the material within a given region can be discerned through traditional non-destructive techniques, there is also a magnetic component to the post-welded material properties. MOKE results indicate a notable difference in magnetic performance between the base materials, heat affected zones, and weld material. Non-destructive MOKE results are correlated with changes in sensitization, composition, and microstructure that have been determined through a variety of traditional, destructive metallography and magnetometry techniques.
3:25 PM
Modeling the Magnetostructural Interactions in Austenitic Steels at the Quantum Mechanical Level: Michelle Johannes1; Noam Bernstein1; Edwin Antillon1; 1Naval Research Laboratory
Using density functional theory, we show that including magnetic properties is *always* important to properly model structural behavior. Since Fe, the primary component of steels has a distance-dependent exchange constant, the bcc Fe-Fe interactions are ferromagnetic and easy to model, while the fcc Fe-Fe interactions are antiferromagnetic and thereby frustrated. The frustration makes austenitic steels paramagnetic which we show is not properly modeled by non-magnetic calculations. We will show how to properly model austenitic steels within DFT and also show examples of how other constituent elements (Mn, Ni, Cr) further complicate the situation.
3:45 PM
Processing of Vitreous Fe-based Wires into Nanostructured Soft Magnetic Material: Ayodele Olofinjana1; James Kern2; Nyok Voo3; 1University of the Sunshine Coast; 2The Welding Institute; 3Universiti Brunei Darussalam
Ribbon shaped metallic glass annealed into nanocrystalline are known to exhibit unique soft magnetic properties. The magnetic softness is attributed to the averaging of the magneto-crystalline anisotropy due to the crystals smaller than the magnetic exchange correlation length. Since wire-shaped metallic glass are known exhibits uniquely soft magnetic properties, this work is, therefore, aimed at studying the devitrification of wire-shaped vitreous alloys. The devitrification of the wires were followed in a differential scanning calorimeter. The devitrification process is typically represented by two thermal events as event markers to follow the nano-crystallisation process. It is shown that only those compositions with large peak separations can be annealed to a single-phase nanocrystalline structure with an average grain size 10 -15nm. The formation of the nanostructure is guided using DSC peak separation and XRD line broadening is used to confirm the existence of nanosized α-Fe(Si) similar to the structure in magnetically soft finemet.
4:05 PM
Rapid Thermal Processing of Amorphous and Nanocrystalline Soft Magnetic Alloys: Paul Ohodnicki1; Ahmed Talaat1; David Greve2; 1University of Pittsburgh; 2DWGreve Consulting
Current state of the art soft magnetic materials for medium frequency and high power applications are metal amorphous nanocomposite (MANC) alloy systems manufactured through partial devitrification of an initially amorphous precursor. Recent work has demonstrated the potential to dramatically increase the number of crystalline nuclei that form through rapid thermal annealing processes, thereby producing refined microstructures with enhanced soft magnetic performance. In this work, we explore both conventional and novel rapid thermal annealing techniques including flash annealing as well as RF electromagnetic radiation assisted processing. A comparison of traditional and various rapid thermal annealing approaches will be presented along with the results of structural and magnetic property characterization. The future outlook for the application of novel thermal processing strategies will also be discussed in detail.