J. Phys. Colloques
Volume 51, Numéro C1, Janvier 1990Proceeding of the International Congress
Intergranular and Interphase Boundaries in materials
|Page(s)||C1-77 - C1-82|
GRAIN BOUNDARY CHEMISTRY IN Ni3Al AND Ni3SiI. BAKER1, E.M. SCHULSON1, J.R. MICHAEL2 et R.A. PADGETT3
1 Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, U.S.A.
2 Bethlehem Steel Corporation, Homer Research Laboratories, Bethlehem, PA 18016, U.S.A.
3 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 03781, U.S.A.
Measurements of the Ni/Al ratio at grain boundary regions in Ni3Al have been performed, using x-ray microanalysis of thin foils in a scanning transmission electron microscope, as a function of both alloy stoichiometry and the addition of boron. It is shown that whilst grain boundaries of Al-rich and stoichiometric Ni3Al have a composition similar to the matrix composition, boundaries in Ni-rich Ni3Al can be highly Ni-enriched. The addition of B to Ni3Al produces Ni enrichment in grain boundaries, the extent of which increases with increasing Ni content of the alloy. Also Auger electron spectrometry has been used to show that B segregates to the grain boundaries irrespective of the Ni : Al ratio. The chemistries of grain boundaries in Ni-rich Ni3Si (Ni3Si only exists on the Ni-rich side of stoichiometry), with and without B, have also been measured by AES. The results are similar to those from Ni3Al, that is, the grain boundaries are enriched in Ni and the addition of B further increases this Ni-enrichment. The implications of these results on the degree of grain boundary atomic order and on the ductility of polycrystals are discussed.