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AEM Microanalysis of Phase Equilibria in Ni3Al Intermetallic Alloys Containing Iron

Published online by Cambridge University Press:  25 February 2011

Bruce L. Bramfitt  and
Joseph R. Michael
Bruce L. Bramfitt
Affiliation:
Bethlehem Steel Corporation, Research Department, Bethlehem, PA 18016
Joseph R. Michael
Affiliation:
Bethlehem Steel Corporation, Research Department, Bethlehem, PA 18016
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Abstract

In order to fully exploit the potential of Ni3Al alloys containing iron, it is necessary to characterize the phase relationships at the Ni-rich region of the Ni-Al-Fe ternary phase diagram. Due to the fine scale structures observed, a technique with high spatial resolution is required. X-ray microanalysis in the analytical electron microscope (AEM) provides a sufficiently high spatial resolution to determine the composition of the various phases occurring in this system. In this study, the isothermal section at 1000°C was evaluated in a series of alloys having nickel contents greater than 65 wt%. In Ni3Al, Fe can substitute for either Ni or Al in the ordered face-centered cubic lattice having an Ll2 structure. However, in substituting Fe for Ni one finds that the solubility limit is quickly exceeded at about 5 wt% Fe with the resultant formation of a ordered body-centered cubic (B2) phase at high temperature, which transforms martensitically upon quenching. Also, in substituting Fe for Al, the solubility limit is exceeded at about 5 wt% Fe with the formation of a disordered, face-centered cubic Ni-rich terminal solid solution. Thus, a very narrow range of alloy compositions exist where Fe can substitute for Ni and Al and preserve a single-phase L12 structure. It was found that the maximum solubility of Fe in Ni3Al at 1000°C was 17.3 wtpercnt; at 70.3 wt% Ni and 12.4 wt% Al.

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Articles
Information
MRS Online Proceedings Library (OPL) , Volume 62: Symposium Q – Materials Problem Solving with the Transmission Electron Microscope , 1985 , 201
Copyright
Copyright © Materials Research Society 1986

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