An elastically induced morphological instability of a misfitting precipitate
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Bulk Chromium Concentration (wt.%) Fig. I - - T h e antimony-to-iron Auger peak height ratio plotted as a function of the bulk chromium concentration.
Thus, in agreement with the results of these experiments, we would not expect chromium additions, at the levels in the alloys used here, to have any effect on the amount of segregation. In contrast, chromium additions at these levels do lower the solubility of nickel in iron. I1~ Since we are dealing with alloys where all of the nickel remains in solution, we would expect the nickel segregation to increase as the chromium is added. We finally note that this increase in nickel segregation does not affect the amount o f antimony segregation. It is important to examine previous data in light of these findings and determine if they are consistent with these results. The only other study in which there are sufficient data for comparison is that of Mulford et al. ,[2j which was carried out on steels containing 0.06 wt pct antimony and 0.3 wt pct carbon. They reported that removing chromium caused a significant decrease in the amount of antimony segregation. We previously pointed out that the correct interpretation of this result is the fol-
lowing. 17~ Chromium was the only strong carbide and sulfide former in the steels used in that work. Its removal would allow carbon and sulfur to segregate and compete with antimony for grain boundary sites, thus decreasing the grain boundary composition of antimony. Mulford et a l . [2j also found that removal of chromium decreased nickel segregation. In a previous publication, Ivl it was suggested that this effect was completely a result of site competition between nickel, carbon, and sulfur. Although these effects undoubtedly contribute to the decrease in nickel segregation, the results in this present study show that part of this decrease was also a result of a decrease in the nickel activity caused by removing the chromium. In conclusion, this study has shown that chromium additions to Fe-Ni alloys doped with antimony have no effect on the amount of antimony segregation to grain boundaries. However, chromium additions do increase the amount of nickel segregation. These results can be explained by the effect of chromium on the activity of nickel and antimony in iron.
REFERENCES 1. H. Ohtani, H.C. Feng, C.J. McMahon, Jr., and R.A. Mulford: Metall. Trans. A, 1976, vol. 7A, pp. 87-101. 2. R.A. Mulford, C.J. McMahon, Jr., D.P. Pope, and H.C. Feng: Metall. Trans. A, 1976, vol. 7A, pp. 1269-74. 3. M. G u n m a n n , P. Krahe, F. Abel, G. Amsel, M. Bruneaux, and C. Cohen: Metall. Trans., 1974, vol. 5, pp. 167-77. 4. P. Gas, M. Guttmann, and J. Bernardini: Acta Metall., 1982, vol. 30, pp. 1309-16. 5. C.L. Briant and A.M. Ritter: Acta Metall., 1984, vol. 32, pp. 2031-42. 6. C.L. Briant: Acta Metall., 1987, vol. 35, pp. 149-53. 7. C.L. Briant: Mater. Sci. Technol., 1988, vol. 4, pp. 956-66. 8. M. Nageswararao, C.J. McMahon, Jr., and H. Herman: Metall. Trans., 1974
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