Elastic constants of some transition- metal- disilicide single crystals
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I.
INTRODUCTION
MOST transition-metal elements combine with Si, and disilicides MSi2 are fabricated by melting. Transition-metal disilicides have various crystal structures. For example, MoSi2, WSi2, and ReSi2 have a tetragonal CIIB structure; VSi2, CrSi2, NbSi2, and TaSi2 exhibit a hexagonal C40 structure; and TiSi2 and ZrSi 2 have orthorhombic C54 and C49 structures, respectively. CoSi 2 exhibits a cubic C I structure. Transitionmetal disilicides with a relatively low density generally exhibit high-melting temperatures and high-oxidation resistance at high temperatures. They are thus expected to be candidates for high-temperature structural application. Recently, some of the transition-metal-disilicide single crystals have been fabricated using a floating zone method, and mechanical properties like compression strength of MoSi2 It'2'3] and WSi2131 have been studied using single crystals. Elastic constants of materials are physical constants from which elastic behavior of the materials are explained, elastic properties of dislocations are understandably theoretical, and fracture toughness is calculated using linear fracture mechanics. Elastic constants are also one measure to represent interaction forces between atoms. The elastic constants, which have been calculated from the ultrasonic wave velocities measured by a pulse echo method for single crystals of MoSi2 and WSi2 as well as TiAI3 and ZrA13 with a low density and highoxidation resistance at high temperatures have been reported. 14'51 In this work, the elastic constants of CrSi2, VSi2, TiSi2, and CoSi2 have been studied using single crystals. CrSiz and VSi2 with a hexagonal C40 structure have a melting point of about 1728 and 1950 K and a density of 4.98 and 4.63 g / c m 3, respectively. TiSi2 and CoSi2 with orthorhombic C54 and cubic C1 structures exhibit MORIHIKO NAKAMURA, Supervising Researcher, is with the National Research Institute for Metals, Meguro-ku, Tokyo 153, Japan. Manuscript submitted February 4, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
a melting temperature of about 1800 and 1600 K, and a density of 4.03 and 4.95 g / c m 3, respectively. The density of these intermetallics was estimated from the lattice parameters t61 and atomic weight. The elastic constants of their single crystals have not been studied because of the difficulty of fabrication of their large single crystals. We fabricated large single crystals using a floating zone method and obtained their elastic constants by measuring ultrasonic wave velocity in a single crystal. The elastic constants of the Ti3Sn single crystal, which is an intermetallic with good ductility even at room temperature, have been examined in comparison with those of the silicides. Ti3Sn has the same hexagonal D019 structure as Ti3A1 which is also a candidate for heat-resistant materials.
II.
EXPERIMENTAL PROCEDURE
Single crystals with a diameter of about 10 mm and a length of 50 to 100 mm were fabricated in the same method as in previous articles. 14,51 The single crystals were annealed at 1273
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