An investigation of superplasticity in a thermomechanically processed U-6nb (α + γ2) alloy
| Autor: | G. M. Ludtka, R. L. Bridges, J. L. Griffith, R. E. Oakes, G. Mackiewicz-Ludtka |
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| Rok vydání: | 1993 |
| Předmět: | |
| Zdroj: | Metallurgical Transactions A. 24:379-388 |
| ISSN: | 2379-0180 0360-2133 |
| DOI: | 10.1007/bf02657325 |
| Popis: | A uranium-6 niobium alloy was shown to exhibit superplasticity. A thermomechanical processing (TMP) sequence was used to develop the ultrafine grain size essential for superplastic behavior. Strain-rate sensitivity, maximum elongation, and flow curve data indicated that this alloy is superplastic above the monotectoid temperature (647 C) in the equilibrium [gamma][sub 1], single-phase, temperature regime. The existence of superplasticity in the single-phase temperature regime was explained by the presence of metastable [gamma][sub 2] at these higher temperatures. Sluggish niobium diffusion and the resultant slow dissolution kinetics were shown to be responsible for this anomalous-single-phase superplastic behavior. An engineering elongation of 658 pct was obtained at 685 C for a constant true strain rate of 2.5 x 10[sup [minus]4] s[sup [minus]1], which required an initial flow stress of only 2.8 MPa. A grain growth kinetic study, along with flow curve information, has also shown that superplastic forming (SPF) must be completed within 2 hours at 670 C to obtain maximum ductility with the lowest forming pressure. |
| Databáze: | OpenAIRE |
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