Designing New Structural Materials Using Density Functional Theory: The Example of Gum Metal TM
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Designing New Structural Materials Using Density Functional Theory: The Example of Gum Metal™ H. Ikehata, N. Nagasako, S. Kuramoto, and T. Saito Abstract As an example of the application of density functional theory (DFT) to materials design, we describe our use of ab initio calculations based on DFT to develop a new structural material: Gum Metal™, a novel, multifunctional titanium alloy with a low Young’s modulus and high strength. We first carried out calculations on elastic constants in several Ti-X binary alloys to obtain the basic principles on which to determine the compositional limitations of an alloy with a low modulus. The elastic properties in the Ti-based binary alloys were successfully estimated by ab initio calculations, with the result implying absolute elastic softening at the valence electron number per atom, e/a, of 4.24. We also studied the effects of additional elements experimentally and, by comparison with electronic-structure calculations, found two more key parameters (approximately representing bond strength and electronegativity), critical for the design of practical elastic properties. We discuss dislocation-free plastic deformation of Gum Metal and its relation to the absolute elastic softening at an e/a value of 4.24, and finally we discuss the prospects for future applications of DFT in structural materials. Keywords: elastic properties, simulation, structural.
Introduction Recent advances in computer calculation techniques and hardware technology have accelerated theoretical approaches to developing new materials. Trial-and-error approaches are still needed to finely adjust the functions of developed materials to practical applications, but in some cases, the basic direction for materials development can be obtained from theoretical and computational considerations. In particular, calculations based on density functional theory (DFT) can be used to
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predict physical behavior that originates from the nature of atomic bonding; thus quantities such as electronic structure and elastic properties have been studied in metals and alloys using DFT from a fundamental perspective. Such calculations have recently been made in several alloy systems to predict their elastic properties in practical uses.1–12 DFT can also be applied to predict certain aspects of the plastic behavior of materials; ideal strengths or dislocation behaviors of structural materials
have been calculated.13–18 However, the direct application of DFT to mechanical behavior is restricted to specific cases, because plastic deformation or fracture in structural materials is a complex phenomenon involving many factors. There is not a long history of DFT application to predict the properties of a material, thus there are few review articles. Kawazoe reviewed several typical examples of DFT calculations that could be used to predict physical, chemical, and mechanical properties of some materials.19 In this article, we describe a successful example of the application of DFT to the design of a new structural material. Specif
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