On the Phenomenon of Stress Drop During Hot Deformation of ZrTiAlV Alloy
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onium alloys are widely used in nuclear industry due to their low probability of neutron capture and excellent resistance to water or vapor corrosion under high-temperature and high-pressure environments. To broaden the application of Zr alloys in other industries, a series of new ZrTiAlV alloys have been recently developed.[1–3] These alloys with high strength and good ductility can be used as advanced structural materials for a number of aerospace applications. The mechanical properties of the ZrTiAlV alloys are dependent on the microstructure and texture developed during manufacturing processes. Therefore, it is necessary to investigate the hot deformation behavior for the control of microstructure. The hot deformation behavior of 47Zr-45Ti-5Al-3V alloy with a coarse grain structure in the b phase field has been investigated.[4] It was found that the flow behavior of this alloy was considerably different from that of the other Zr-alloys.[5–11] At high strain rates of 0.1 to 1 s1 and low deformation temperatures ranging from 1123 K to 1173 K (850 C to 900 C), a pronounced stress drop occurred at the beginning of deformation, followed by a slow decrease in flow stress with increasing strain. A similar phenomenon was YUANBIAO TAN, Ph.D. Student, WENCHANG LIU, RIPING LIU, and XIANGYI ZHANG, Professors, and HUI YUAN, Associate Professor, are with the Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 26, 2013. Article published online September 28, 2013 5284—VOLUME 44A, DECEMBER 2013
observed in hot-deformed Ti-6.8Mo-4.5F-1.5Al,[12] Ti22Al-25Nb,[13] and Ti-25V-15Cr-0.3Si alloys,[14] which was attributed to the rapid generation of mobile dislocations from grain boundary sources.[12,15] In the current study, the ZrTiAlV Alloy was annealed at 1123 K and 1323 K (850 C and 1050 C) for 30 minutes each, to produce different grain sizes. The effect of initial grain size on the hot deformation behavior was investigated. Sponge Zr (Zr + Hf ‡ 99.5 wt pct), sponge Ti (99.7 wt pct), industrially pure Al (99.5 wt pct), and V (99.9 wt pct) were used to prepare the 47Zr-45Ti-5Al-3V (wt pct) alloy. The alloy was melted three times using a vacuum consumable electro-arc furnace to ensure a uniform chemical composition. The cast ingot was multiply forged to completely break the cast structure after homogenization at 1323 K (1050 C) for 1.5 hour. The alloy billet was heated to 1203 K (930 C) and hot-forged into bars of 43 mm in diameter. In order to obtain different grain sizes before hot deformation, the bars were annealed at 1123 K and 1323 K (850 C and 1050 C) for 30 minutes in a tubular vacuum heat-treatment furnace with a protective argon atmosphere, followed by water quenching. The average grain sizes were measured to be 224 and 450 lm, respectively. Cylindrical compression specimens of 12 mm in height and 8 mm in diameter were machined from the annealed bars. Hot
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