The structure and properties of thermomechanically treated β-III titanium |
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Authors: | D Kalish H J Rack |
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Affiliation: | (1) Bell Telephone Laboratories, Inc., Norcross, Ga.;(2) Sandia Corp., Albuquerque, N. M. |
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Abstract: | Beta-III titanium (Ti-11.5Mo-5.5Zr-4.5Sn) was solutionized above the β-transus, water-quenched and deformed by rolling at room temperature. The deformation accelerated the aging kinetics at all temperatures up to the β transus. The thermomechanically treated (TMT) alloy always had higher strength than the conventionally heat treated (CHT) alloy; the effect being most marked when the aging product was normally α in a β matrix. In addition, the ductility and notched impact resistance of TMT β-III was greater than that of the CHT alloy in the over-aged condition. The TMT did not alter the morphology of the ellipsoidal α phase formed at low aging temperatures and short aging times, respectively. Here the strengthening increase is attributed to strain hardening of the initial β + ω microstructure. The deformation did substantially change the morphology of the Widmanstätten α phase that formed at higher aging temperatures. In particular, the Widmanstätten α plates were much finer and the β grain boundaries were no longer a preferred precipitation site following TMT. At the highest aging temperatures, the TMT material developed a cell structure of about 1 μ in diameter. |
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