Low frequency damping and ultrasonic attenuation in Ti 3 Sn-based alloys
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Studies of high-temperature alloys in the Ti-Sn system based on the intermetallic compound Ti3Sn have identified alloys that damp strongly both at low frequencies (0.1 to 10 Hz) and high frequencies (5 to 20 MHz). The low frequency damping behavior shows loss factors as high as 0.04 at room temperature and Young's moduli that rise with temperature from 40 °C to 100 °C for two alloys. Although the basic mechanism or mechanisms of energy dissipation are presently unknown, the alloys are notable for unusual shapes of microhardness indentations. The deformations imply that large reversible strains can occur at temperatures from 23 °C to 1150 °C.
I. INTRODUCTION Mechanical damping is of interest both because of the need for basic scientific understanding and because energy absorption can be used in many practical applications such as minimizing noise that is distracting or harmful to human beings, minimizing vibrations that would be harmful to equipment, and reducing unwanted acoustic reflections and emissions. A number of metal alloys have long been known for their high damping capacity. These include a variety of dilute Mo alloys,1 Cu-Zn alloys,2 and Mn-Cu alloys.3 It is also noteworthy that the well-known shape-memory alloy NiTi also shows strong damping at room temperature.4 The purpose here is to report on two alloys in another high-damping system (Ti—Sn) that have some unusual features and a high melting temperature (1590 °C). We describe the damping capacity and what is known structurally about two alloys studied here and discuss other related compositions that have some key properties in common and are therefore prime candidates for further study. Motivation The origin of interest in the alloys studied here was the failure to determine elastic constants in highfrequency (5 to 20 MHz) pulse-echo measurements.5 Reflections from acoustic pulses could not be identified after a 1 cm travel distance in Ti8OSn2o, Ti78Sn22, and Ti75Sn2iV4. Subsequent work with the same technique6 showed similar attenuation in Ti72SnlgAlio and in a different system, Ti36Cr54Alio. Two binary compositions, Ti3Sn and Ti 87 Sni 3 , which bracket those that showed the a 'Present
address: Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180-3590. J. Mater. Res., Vol. 9, No. 6, Jun 1994 http://journals.cambridge.org
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strong attenuation behaved normally in that their elastic constants could be determined.
II. EXPERIMENTAL PROCEDURE A. Preparation of samples Samples were arc melted into disk-shaped ingots using the highest purity components that were reasonably available. Titanium was 99.99% pure and tin > 99.999%. Purities of other elements in alloys to be cited for comparison were (Al) 99.9999%, (Cr) 99.99%, (Nb) 99.99%, and (V) 99.9%. Interstitials in wt. ppm were (C) 100, (N) 15, and (O) 500 for Ti80Sn20, and (C) 100, (N) 25, and (O) 1000 for Ti7gSn22. Samples were annealed at 1350 °C in Ar-filled SiO2 ampules that included a small piece of Y to getter oxygen. Micro
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