A Self-Consistent Approach for Modeling the Flow Behavior of the Alpha and Beta Phases in Ti-6Al-4V
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CONVENTIONAL hot working processes such as forging and extrusion are used widely to produce structural and engine parts in the aerospace industry. Sophisticated modeling and design tools are now being developed to reduce cost and improve quality through the control of microstructure and reduction of defects. To this end, much research is being conducted to quantify the constitutive behavior of workpiece materials and to analyze plastic flow at high temperatures.[1–4] Although numerous studies on the deformation behavior of two-phase alloys have been reported,[5–7] a complete understanding of these materials has yet to be established. The macroscopic plastic-flow behavior of two-phase alloys is controlled by the properties of the individual crystallites of the two phases. In a two-phase alloy, the deformation rate and flow stress may vary from one phase to the other as well as within the individual microconstituents. Knowledge of such nonuniformities is critical in understanding the development of local JEOUNG HAN KIM, formerly Graduate Student, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea, is now with the Structural Materials Division, Korea Institute of Materials Science, Changwon 641-010, Korea. S.L. SEMIATIN, Senior Scientist, Materials Processing/Processing Science, is with the Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/ RXLM, Wright-Patterson Air Force Base, OH 5433-7817. YOU HWAN LEE, Senior Researcher, is with the Wire Rod Research Group, Technical Research Laboratories, POSCO, Pohang 790-784, Korea. CHONG SOO LEE, Professor, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted October 27, 2009. Article published online December 8, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation inhomogeneities, lattice rotations, cavitation, and crystallographic texture, which are the major variables controlling alloy final properties.[8] Hence, it is necessary to quantify the properties of each phase to develop accurate modeling and simulation tools. In previous research, Semiatin et al.[8] analyzed plastic-flow behavior during hot working of the a/b titanium alloy Ti-6Al-4V in the context of a self-consistent approach. Subsequently, Vo et al.[9] applied a similar approach for the near-a alloy IMI-834. In both efforts, the constitutive relations for the individual a and b phases were based on measurements by Oikawa and colleagues[10–13] for binary Ti-Al and Ti-V alloys. In particular, the proposed constitutive relations were formulated in terms of strength coefficients that depend on Al and V content. However, the chemical compositions of the a and b phases in Ti-6Al-4V and IMI-834 alloys are different from the simple binary alloys investigated by Oikawa and colleagues. Therefore, the strength coefficients for each phase were modified in terms of so-called Al and V ‘‘equivalents’’ to account for t
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