Probing the Relationship of Long-Range Order in Nanodomain FeCo Alloys with Ternary Additions Using Neutron Diffraction
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INTRODUCTION
FeCo alloys are industrially important engineering materials due to their very high saturation magnetization and Curie temperature. These alloys play an important role in applications requiring soft magnetic materials, such as electrical generators and motors. Further examples are transformer cores, magnetically driven actuators, pole tips for high field magnets, and solenoid valves. For many industrial applications, the challenge is increasing the tensile strength and ductility of FeCo alloys while maintaining magnetic performance. Methods used to meet these challenges include alloy design (e.g., addition of certain ternary metals such as Ni, V, Nb, Ta, Cr, and Mo), annealing, and advanced deformation processing. However, modern applications require even better mechanical and magnetic performance. Recent years have seen a reawakened interest in FeCo alloys due to the increased demands of modern electrical
RALPH GILLES and MICHAEL HOFMANN, Senior Scientists, are with the Technische Universita¨t Mu¨nchen, ZWE, FRM II, 85747 Garching, Germany. Contact e-mail: [email protected] YAN GAO, FRANK JOHNSON, and LUANA IORIO, Senior Scientists, and MICHAEL LARSEN, Technician, are with GE Global Research, Niskayuna, NY 12301. FENG LIANG, Scientific Staff Member, is with the Technische Universita¨t Mu¨nchen and the Department of Nuclear Physics, CIAE, 102413 Beijing, P.R. China. MARKUS HOELZEL, Scientific Staff Member (Postdoc), is with the Technische Universita¨t Mu¨nchen and the Technische Universita¨t Darmstadt, FB Material- und Geowissenschaften, Petersenstr. 23, 64287 Darmstadt, Germany. BRUNO BARBIER, Scientific Staff Member, is with the Universita¨t Bonn, Steinmann Institut fu¨r Geologie, Mineralogie, Pala¨ontologie, 53115 Bonn, Germany. This article is based on a presentation given in the symposium ‘‘Neutron and X-Ray Studies of Advanced Materials,’’ which occurred February 15–19, 2009, during the TMS Annual Meeting in San Francisco, CA, under the auspices of TMS, TMS Structural Materials Division, TMS/ASM Mechanical Behavior of Materials Committee, TMS: Advanced Characterization, Testing, and Simulation Committee, and TMS: Titanium Committee. Article published online August 8, 2009 1144—VOLUME 41A, MAY 2010
power generation and distribution equipment.[1,2] These demands are especially severe in electrical applications for extreme environments. On the other hand, FeCo alloys pose interesting questions because of their structural and physical properties, especially in nanostructured systems.[3] The development of FeCo alloys with low cobalt content (17 to 35 wt pct Co) was mainly driven to lower the cost of the alloy[4] while keeping the desired magnetic properties. In addition, lower Co levels enhance ductility and toughness. The mechanical properties of the alloys are directly related to their crystal structures depending on temperature. At high temperatures, the two elements, Fe and Co, are distributed randomly on the sites of a bodycentered cubic (bcc) lattice (A2 type structure, also Figure 1). For Co
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