Single crystals and cold-swaged polycrystalline specimens of Gum Metal of Ti-36Nb-2Ta-3Zr-0.3O (mass %) have been compressed with the stress-relaxation test in the temperature range from 77 K to 450 K. In both single crystals and cold-swaged specimens, the yield stress decreases with increasing temperature rapidly to the room temperature and then gently above it forming a plateau at high temperature. The activation analysis of plastic deformation showed that the applied shear stress dependence of activation enthalpy and that of activation volume for single crystals and those for cold swaged specimens are almost identical if we shift the stress scale by about 120 MPa, meaning that the basic deformation mechanism is common to both samples. The above results are contradictory with the previously proposed non-dislocation deformation mechanism at the ideal shear strength, but consistent with the established features of usual bcc alloys, i.e., the deformation is governed by the Peierls mechanism at low temperature and by defect hardening at high temperature. τ χ − χ and ψ − χ relations of single crystals showed a typical slip asymmetry seen in bcc metals, where slip in Gum Metal belongs to the {112} slip type as in binary Ti-Nb single crystals reported previously (S. Hanada et al.: Metall. Trans. A 16 (1985) 789). Yielding by massive {332}〈113〉 twin formation in single crystals at low temperatures was observed for the rst time in Gum Metal.
Compression deformation and stress relaxation tests have been made over a wide temperature range for Ti-based bcc alloy single crystal of Gum Metal composition to elucidate the deformation mechanism. The shear yield stress decreases rapidly with increasing temperature with decreasing slope above room temperature, tending to level off. Activation analysis showed that the activation volume becomes smaller than 10 b 3 (b: the Burgers vector) at high stress, indicating that the deformation is controlled by the Peierls mechanism at low temperature. Similar results have been obtained also for severely cold-swaged polycrystalline Gum Metal with the similar composition. These results contradict the generally accepted dislocation-free mechanism of Gum Metal.
An apparatus for deformation of solids in liquid 3He is constructed. Either tensile deformation or compression of a specimen can be performed by exchanging the assemblies in the 3He pot which has a capacity of about 30 cm3. The pulling rod for transmitting load from the tensile testing machine to the specimen runs inside the outlet tube of 3He, being isolated from 4He bath and almost free from mechanical friction. To measure the change in flow stress with the supernormal transition of superconducting metals, a superconducting magnet is mounted outside of the vacuum chamber which separates the 3He pot and the 4He bath. Under an applied load for plastic deformation the system is stably operative down to 0.6 K, while the lowest temperature achieved is 0.5 K. Some results on Ta and NaCl are presented.
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