High Strength Conductors and Structural Materials for High Field Magnets
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High Strength Conductors and Structural Materials for High Field Magnets Ke Han1, Rongmei Niu1, Jun Lu1, and Vince Toplosky1 1 Florida State Univ, National High Magnetic Field Laboratory, Tallahassee, FL, United States, U.S.A. ABSTRACT One important approach to increasing High magnetic fields (HMF) beyond what is now possible is to improve the properties of various composite materials used as both conductors and structural support. Typical conductors for high field magnets are Cu-based metal-metal composites. To achieve high mechanical strength, these composites are fabricated by cold deformation, which introduces high densities of interfaces along with lattice distortions. During the operation of a magnet, mechanical load, high magnetic field, extreme temperatures and other stressors are imposed on the materials, causing them to be further “processed”. The composite conductors in a magnet, for example, may undergo high temperatures, which reduce lattice distortions or soften the material. At the same time, HMF may increase lattice distortion, leading to a complex change in interface characteristics. Both the mechanical properties of the conductors, like the tensile and yield strength, and the electric conductivity of the composites are closely connected to changes in lattice distortion and interface density. Understanding these changes helps us to assure that materials can operate in optimized conditions during most of magnets’ service life. Maximizing service life is critical, given the high cost of building and operating high field magnets. The goal of this paper is to 1) show our understanding of changes that occur in the properties of selected materials during the fabrication and under HMF and 2) to discuss how those changes relate to the microstructure of these materials and consequently to the service life of high field magnets. INTRODUCTION High field magnets have become powerful tools to study materials. High magnetic fields (HMF) are only achievable through the use of specialized function materials, like high-strength conductors and insulators, and in some cases, high-strength structural materials. The performance of high field magnets depends heavily on quality of the materials used as conductors, insulations and reinforcements. The selection, development and characterization of these materials vary with type of magnet and the conditions under which it will be used [1-6]. When high performance conductors are used, both mechanical properties and electrical conductivity must be taken into consideration. At any given level of electrical conductivity, raising the level of mechanical strength potentially raises the strength of the magnetic field. Understanding the performance of materials in a high field magnet is made more complex by the variety of changes in material properties that can be induced by exposure to cryogenic conditions, high operation temperatures, high strain rates, and HMF operations in general. Many of these changes have been studied, but are not well understood. Other changes, like the magn
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