The effect of cold rolling on the fatigue properties of Ti-6Al-4V
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are enough differences that the more accurate solution is necessary for detailed analysis of the process.
This research was performed under the auspices of the Division of Materials Research of the National Science Foundation.
Mechanical Properties
Yield Strength 0.2 Pct Offset MPa
Ultimate Strength MPa
Elongation Pct in 25.4 mm
790 884
880 968
12.5 6.25
As-received 20 pct cold reduction
9OO
REFERENCES 1. J.P. Stark: Acta Metall., 1983, vol. 31, p. 2083. 2. B.S. Lira and J.P. Stark: Acta Metall., 1984, vol. 32, p. 915, and Metatl. Trans. A, 1983, vol. 14A, p. 2557. 3. M.E. Aly and J.P. Stark: Acta Metall., 1984, vol. 32, p. 907. 4. J.C. Fisher: J. Appl. Phys., 1951, vol. 22, p. 74. 5. R. T. P. Whipple: Phil. Mag., 1954, vol. 45, p. 1225. 6. J. P. Stark: Acta Metall., 1984, vol. 32, p. 535.
~800 []
v
600
40(3
3o~@i
Ti - 6AI - 4V o As received o Cold rolled
........
' 104
........
~ 105
........
Number of Cycles, to Failure,
S.Z. LIU, K. MINAKAWA, B. SCHOLTES, and A. J. McEVILY Cold working a metal or alloy generally has the effect of improving the S / N properties I as a result of the increase of the flow stress due to an increase in dislocation density. However, in the case of the titanium alloy Ti-6AI-4V cold work can have a deleterious effect on the fatigue properties as will be discussed in this note. The Ti-6AI-V alloy used in these experiments was obtained in sheet form in a thickness of 1.27 mm. Two conditions of the material were used in the fatigue test program. In one case the material was tested in the as-received (millannealed) condition. In the other case the material was reduced in thickness by cold rolling in a laboratory rolling mill in five passes to a total reduction of 20 pct, i.e., the final thickness was 1.02 mm. Axial fatigue specimens were prepared from the sheet material which were 9 m m wide in the test section. Prior to fatigue testing the test sections were polished by standard metallurgical procedures to a mirrorlike finish. The fatigue tests were carried out in a Sonntag SF-1 testing machine at a fixed frequency of 30 Hz. R = 0.05 test conditions were used, and testing was done in laboratory air. The tensile properties of the alloy were determined for each of the test conditions. These are given in Table I and reflect the usual increase in monotonic strength properties with cold work. The results of the fatigue tests are shown in Figure 1, and it is noted that cold rolling has led to a marked and perhaps surprising reduction in the fatigue strength of Ti-6A1-4V. Why has cold rolling had such an adverse effect on the fatigue properties of this alloy? The answer to this question S.Z. LIU is with Shenyang Aircraft Corporation, Shenyang, China. K. MINAKAWA, Assistant Professor, and A.J. McEVILY, Professor, are with the Metallurgy Department, University of Connecticut, Storrs, CT 06268. B. SCHOLTES is Research Associate, Institute f/ir Werkstoffkunde, University of Karlsruhe, Karlsruhe, West Germany. Manuscript submitted August 3, 1984. 144--VOLUME 16A, JANUARY 1985
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