Anomalous transformation-induced deformation in 〈1 1 0〉 textured Gum Metal |
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Authors: | JW Morris Y Hanlumyuang M Sherburne E Withey DC Chrzan S Kuramoto Y Hayashi M Hara |
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Affiliation: | 1. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA;2. Toyota Central R&D Laboratory, Nagakute, Aichi 480-1192, Japan |
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Abstract: | Tensile tests on single crystals of Gum Metal (Ti–36Nb–2Ta–3Zr–0.3O (wt.%)) showed, anomalously, that while a stress-induced β(bcc) → α″(orthorhombic) transformation occurred in a crystal pulled in the 〈1 1 0〉 direction, (1) no transformation was observed in crystals pulled in the 〈1 0 0〉 or 〈1 1 1〉 directions and (2) little or no transformation occurred in severely worked rods, which are polycrystals with very strong 〈1 1 0〉 texture. Analysis of the energetics of the β → α″ transformation offers straightforward explanations: (1) an α″ precipitate has zero elastic energy if it forms as a thin plate with the habit {1 1 1.5}; a 〈1 1 0〉 tensile load significantly decreases the energy of this plate; loading along 〈1 0 0〉 or 〈1 1 1〉 is less effective; (2) while worked rods have a strong 〈1 1 0〉 axial texture, the perpendicular planes are severely distorted, increasing the elastic energy of α″ and inhibiting the transformation. |
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