
Table II. The Nominal Volume Percent of Oxide Dlspersold In
the ODS Alloys Plotted in Figures 7 and 8
Nominal Volume
Alloy Percent Dispersoid
TD NiCr 3 2
MA 7544,5 1
TD NiCr Sheet 6 2
MA 6000E 2.5
An interesting question is whether or not the 7'
precipitates in MA 6000E play a major role in creep
strengthening at 1093 ~ or higher. The ,/solvus
temperature in MA 6000E is 1175 _ 5 ~ as deter-
mined by differential thermal analysis, and accordingly,
3" precipitates are very much a part of the micro-
structure at 1093 ~ However, from Fig. 9 it can be
seen that above 1000 ~ the rupture strength of MA
6000E drops off much more slowly with temperature
than those of either Mar M200 or Udimet 700, and
above about 1093 ~ the rupture strengths of the 7'
strengthened superalloys drop to insignificant levels. In
fact, the temperature dependence of the rupture
strength of MA 6000E at the higher temperatures is very
similar to that of the ODS alloy MA 754 which contains
no 3". Thus, it appears that the major creep strengthen-
ing particles are the dispersed oxides at 1093 ~ or
higher in MA 6000E.
Finally, it also appears from Figs. 7 and 8 that MA
6000E is far superior than the other ODS nickel-base
alloys. The reasons for this unfortunately are not
completely apparent at this time. The answer does not
lie with the oxide volume fraction or size. The size
distributions of the intentional Y203 particles in all the
alloys in these figures are similar. Table II compares the
aimed volume percents of the Y203 particles for these
alloys. As can be seen MA 6000E is not overly endowed
with Y203 in comparison with the other alloys. The
grain size and the grain aspect ratio may be a factor, as
proposed by Wilcox and Clauer, 2~ since MA 6000E has
a very coarse and long grain size. However, the relative
importance of this factor is not known for the alloys in
discussion. Also, the total solute element content in MA
6000E is much higher than the solute contents in the
other alloys, and therefore, solid solution effects can
certainly be a factor.
CONCLUSIONS
1) The stress dependence of the creep rate is very
sharp in MA 6000E and increases with temperature.
The apparent creep activation energy measured at
760 ~ is much larger than the self-diffusion energy.
2) Stress rupture in this large grain size material is
transgranular and crystallographic cracking is observed.
The elongation to failure is low and decreases with
increasing temperature.
3) Several strengthening concepts are successfully
incorporated in MA 6000E. At an intermediate tem-
perature the creep strength is apparently controlled by
the high volume fraction of 3" precipitates, and the
contribution to the creep strength from the oxide
dispersion is small. At an elevated temperature, the
creep strength is derived from the inert oxide
dispersoids.
ACKNOWLEDGMENT
We wish to thank Tom Glasgow of NASA-Lewis for
helpful discussions and Ola Ajaja for help with electron
microscopy. We are grateful to NASA-Lewis for sup-
porting this work under grant NSG-3050. We also
acknowledge the partial support of the National Science
Foundation under Grant NSF-DMR77-11281 and
INCO for supplying the MA 6000E material for study.
Mar M200, Udimet 700 and Inconel Alloy MA 754 are,
respectively, trademark alloys of Martin Marietta Cor-
poration, Special Metals Corporation and the INCO
Family of Companies.
REFERENCES
1. H. F. Merrick, L. R. Curwick and Y. G. Kim: NASA CR-135150,
January 1977 and NASA CR-159493, May 1979.
2. T. E. Howson: Eng. Sci. D. Thesis, Columbia University, New
York, 1979.
3. R.W. Lund and W. D. Nix:
Acta Met.,
1976, vol. 24, p. 469.
4. T. E. Howson, J. E. Stulga and J. K. Tien:
Met. Trans. A,
1980,
vol. IIA, p. 1599.
5. J. D. Whittenberger:
Met. Trans. A,
1977, vol. 8A, p. 1155.
6. J. D. Whittenberger:
Met. Trans. A,
1976, vol. 7A, p. 611.
7. The International Nickel Company, Inc:
High Temperature, High
Strength Nickel Base Alloys,
3rd ed., New York, July 1977.
8. B. H. Kear, G. R. Leverant and J. M. Oblak:
Trans. ASM,
1969,
vol. 62, p. 639.
9. B. H. Kear:
Order-Disorder Transformation in Alloys, p. 440, H.
Warlimont, ed., Springer-Verlag, New York, 1973.
10. F. Dobes and K. Milicka:
Metal Sci.,
1976, vol. 10, p. 382.
11. O. D. Sherby and P. M. Burke:
Prog. Mat. Sci.,
1967, vol. 13, p.
325.
12. J. Heslop:
J. Inst. Met.,
1962-1963, vol. 91, p. 28.
13. G. A. Webster and B. J. Piearcey:
Met. Sci. J.,
1967, vol. 1, p. 97.
14. D. Sidey and B. Wilshire:
Met. Sci. J.,
1969, vol. 3, p. 56.
15. G. R. Leverant and B. H. Kear:
Met. Trans.,
1970, vol. 1, p. 491.
16. M. Malu: Eng. Sci. D. Thesis, Columbia University, New York,
1975.
17. K. Aning and J. K. Tien:
Mater. Sci. Eng.,
1980, vol. 43, p. 23.
18. R. Lagneborg and B. Bergman:
Met. Sci.,
1976, vol. 10, p. 20.
19. W. J. Evans and G. F. Harrison:
Met. Sci.,
1976, vol. 10, p. 307.
20. B. A. Wilcox and A. H. Clauer:
Trans. TMS-A1ME,
1966, vol.
236, p. 570.
21. A. H. Clauer and B. A. Wilcox:
Met. Sci. J.,
1967, vol. 1, p. 86.
22. J. S. Benjamin and R. L. Cairns:
Mod. Dev. Powder Metall.,
1970,
vol. 5, p. 47.
23. B. A. Wilcox and A. H. Clauer:
Acta Metall.,
1972, vol. 20, p. 743.
24. R. D. Kane and L. J. Ebert:
Met. Trans. A,
1976, vol. 7A, p. 133.
25. R. L. Threadgill and B. Wilshire:
Proc. Conf. on Creep Strength of
Steels and High Temp. Alloys,
p. 8, The Iron and Steel Institute,
London, 1973.
26. P.W. Davies, G. Nelmes, K. R. Williams and B. Wilshire:
Met.
Sci.J.,
1973, vol. 7, p. 87.
27. K. R. Williams and B. Wilshire:
Met. Sci. J.,
1973, vol. 7, p. 176.
28. J. D. Parker and B. Wilshire:
Met. Sci. J.,
1975, vol. 9, p. 248.
29. G. Nelmes and B. Wilshire:
Scr. Metall.,
1976, vol. 10, p. 697.
30. S. Purushothaman and J. K. Tien:
Acta Metall.,
1978, vol. 26, p.
519. 9
31. O. Ajaja, T. E. Howson, S. Purushothaman, and J. K. Tien:
Mater. Sci. Eng.,
1980, in press.
32.
Strength of Metals and Alloys,
P. Hassen, V. Gerold and G.
Kostorz, eds., vol. 1, p. 251, Pergamon Press, Oxford, 1979.
33. R. S. W. Shewfelt and L. M. Brown:
Philos. Mag.,
1977, vol. 35, p.
945.
34. M. Malu: Eng. Sci. D. Thesis, Columbia University, New York,
1975.
1616--VOLUME 11A, SEPTEMBER 1980 METALLURGICAL TRANSACTIONS A