Effect of prior austenitic grain size on stress corrosion cracking of a high-strength steel
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Comparison of Theoretical and Experimental K Values in Aluminum, Nickel, and Copper
T (~ 250
T/TM 0.56
5.92
10 -16
Kr (m2/s) 5.44 • 10-16
1.09
Nickel
350 300 250 200
0.36 0.33 0.30 0.27
6.38 • 1 0 -17 7.4 • 10-18 3.0 • 10-18 5.18 • 10-18
4.62 • 10-26 3.66 • 10-28 1.14 • 10-30 1.04 • l0 33
1.38 2.03 2.63 4.98
X • • •
Copper
200
0.35
5.7
1.5
3.8
• 107
Metal Aluminum
KE (m2/s) X
• 10 -18
• 10 -25
KE/Kr 108 101~ 1012 101s
SFE (mJ/m 2) 200 128 ---78
TM = melting point in K; Kr = theoretical K value; Ke = experimental K value.
Table III. The Observed Activation Energy Values and the Relative Contributions of the Sandstrom and Pipe Diffusion Models
Relative Contributions T
(~ 200 250 300 350
Q
Sandstrom
Pipe Diffusion
(kJ/mole) Q = 292 kJ/mole Q = 126 kJ/mole 150 168 179 183
0.16 0.25 0.32 0.34
0.84 0.75 0.68 0.66
homologous temperatures, as indicated in Table II. This may be related to the process of extraction and/or emission of dislocations from the subgrain boundaries. Thus, we can summarize our results of this study in the following manner: 1. The parabolic equation, established by Sandstrom, to describe the subgrain growth is valid in nickel during recovery at 350 ~ 300 ~ 250 ~ and 200 ~ 2. There are large differences between the theoretical and the experimental K values at these four recovery temperatures. The differences can be rationalized on the basis of two different mechanisms: subgrain growth due to (a) the vacancy mechanism, expected to dominate t h e process at higher temperatures, and (b) the dislocation pipe diffusion mechanism, expected to dominate the process at lower temperatures. REFERENCES 1. J.C.M. Li: J. Appl. Phys., 1962, vol. 33, pp. 2958-65. 2. J.C.M. Li: Recrystallization, Grain Growth and Textures, ASM, Metals Park, OH, 1962, p. 86. 3. R.C. Koo and H.G. Sell: Recrystallization, Grain Growth and Textures, ASM, Metals Park, OH, 1962, p. 97. 4. H. Hu: Trans. AIME, 1962, vol. 224, p. 75. 5. R.D. Doherty and R.W. Cahn: J. Less-Common Met., 1972, vol. 28, pp. 279-96. 6. R.D. Doherty: Met. Sci., 1974, vol. 8, pp. 132-42. 7. P. Faivre and R.D. Doherty: J. Mater. Sci., 1979, vol. 14, pp. 897-919. 8. R.D. Doherty and J.A. Szpunar: Acta Metall., 1984, vol. 32, pp. 1789-98. 9. R. Sandstrom: Acta Metall., 1977, vol. 25, pp. 897-904. 10. R. Sandstrom: Acta Metall., 1977, vol. 25, pp. 905-11. 11. R. Sandstrom, B. Lehtinen, E. Hedman, I. Groza, and S. Karlsson: J. Mater. Sci., 1978, vol. 13, pp. 122%42. 12. S.K. Varma and B.L. Willits: Metall. Trans. A, 1984, vol. 15A, pp. 1502-03. 13. S.K. Varrna and B.C. Wesstrom: J. Mater. Sci. Leg., 1988, vol. 7, pp. 1092-93. METALLURGICAL TRANSACTIONS A
14. S.K. Varma: Mater. Sci. Eng., 1986, vol. 82, pp. L19-L22. 15. S.K. Varma and R.W. Guard: J. Mater. Sci. Lett., 1986, vol. 5, pp. 205-08. 16. S.K. Varma and S.J. Reyes: Mater. Sci. Eng., 1987, vol. 95, pp. L1-L3. 17. Chung-Min Chang, J.R. Serrano, and S.K. Varma: Mater. Sci. Eng., 1988, vol. 100, pp. L15-L18. 18. Chung-Min Chang and S.K. Varma: Acta Metull., 1989, vol. 37, pp. 927-
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