Effect of texture changes on flow softening during hot working of Ti-6Al-4V
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REFERENCES (a)
(b) Fig. 2—Macrographs of aluminum alloy 2024-T851 samples after roomtemperature ECAE at a ram speed of (a) 0.25 mm/s or (b) 25.4 mm/s.
at two different ram speeds are shown in Figure 2. At the lower ram speed (0.25 mm/s), corresponding to a strain rate of approximately 0.01 s⫺1, cracking was noted to a depth of approximately 2.5 mm from the top surface. From the analysis in Reference 6, the tensile damage imposed during a single ECAE pass of a perfectly plastic material through a 90 deg die varies from approximately 0.25 at the top surface to zero at a depth equal to one-fifth of the cross section. Thus, the observed depth of cracking does correlate approximately to that at which the tensile damage factor drops below the critical value of ⬃0.10 determined from the tension tests. The ECAE sample deformed at the higher ram speed of 25.4 mm/s (corresponding to an average strain rate of 1 s⫺1), shown in Figure 2(b), revealed evidence of both gross fracture and shear failure. The fracture was evidenced by wide gaps between “sawteeth” that separated workpiece segments. It may be concluded that the high value of the flow localization parameter at this strain rate (Table I) led to the formation of shear bands during ECAE and that cracking due to tensile damage at the top sample layers propagated along the shear bands. The results of this investigation verify that two distinct types of failure may occur during ECAE. The specific type depends on two material properties—the alpha parameter in shear, ␥ ⬘/m, and the critical tensile damage factor from the Cockcroft-and-Latham criterion. Depending on the specific values of these properties, fracture, shear localization, or a combination of the two may occur.
This work was conducted as part of the in-house research activities of the Metals Processing Group of the Air Force METALLURGICAL AND MATERIALS TRANSACTIONS A
1. V.M. Segal, V.I. Reznikov, A.E. Drobyshevskiy, and V.I. Kopylov: Russ. Metall., 1981, vol. 1, pp. 99-105. 2. V.M. Segal: Proc. 5th Int. Aluminum Technology Seminar, Aluminum Association, Washington, DC, 1992, vol. 2, pp. 403-08. 3. R.Z. Valiev, R.K. Islamgaliev, and I.V. Alexandrov: Progr. Mater. Sci., 2000, vol. 45, pp. 103-89. 4. D.P. DeLo and S.L. Semiatin: Metall. Mater. Trans A, 1999, vol. 30A, pp. 1391-1402. 5. S.L. Semiatin, V.M. Segal, R.L. Goetz, R.E. Goforth, and T. Hartwig: Scripta Metall. Mater., 1995, vol. 33, pp. 535-40. 6. S.L. Semiatin, D.P. DeLo, and E.B. Shell: Acta Mater., 2000, vol. 48, pp. 1841-51. 7. R.L. Goetz and S.L. Semiatin: Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH, unpublished research, 1994. 8. S.L. Semiatin and J.J. Jonas: Formability and Workability of Metals, ASM, Materials Park, OH, 1984. 9. M.G. Cockcroft and D.J. Latham: J. Inst. Met., 1968, vol. 96, pp. 33-39.
Effect of Texture Changes on Flow Softening during Hot Working of Ti-6Al-4V S.L. SEMIATIN and T.R. BIELER The modeling of deformation processes requires accurate descriptions of plastic flo
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