Determination of the Fe-Ni phase diagram below 400°C

Details Determination of the Fe-Ni phase diagram below 400°C Determination of the Fe-Ni phase diagram below 400°C

Apr 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989mta....20..719r&link_type=abstract

Metallurgical Transactions A, Volume 20, Issue 4, pp.719-725

Computer Science

14

Scientific paper

The phase diagram for the Fe-Ni system below 400°C has been determined experimentally in the composition range from 0 to 52 wt pct Ni using analytical electron microscopy techniques. High spatial resolution X-ray microanalysis and electron diffraction were conducted on the Fe-Ni regions of meteorites. Both stable and metastable phase boundaries were defined. Our phase diagram is consistent with the available theoretical diagram in that firm experimental evidence was found for a miscibility gap and an associated, asymmetrical spinodal decomposition region. The spinodal decomposition resulted in a two-phase, isotropic microstructure, as expected. The miscibility gap is a metastable construction arising from the presence of a tricritical point due to magnetic interactions. Our experimental diagram differs from the theoretical diagram in three ways. First, observations of meteorite structures show that Fe-Ni solid solution containing 4.0 wt pct Ni is in local equilibrium with ordered FeNi containing 51.4 wt pct Ni and not Ni3Fe as in the theoretical diagram. Second, our miscibility gap below 400°C, located between 11.7 and 51.9 wt pct Ni at 200°C, is wider than the calculated miscribility gap, especially at the high Ni end. Third, we also find evidence for an ordered structure around ˜25 wt pct Ni. This structure may be either Fe3Ni or a two-phase structure incorporating ordered FeNi.

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