Solidification of undercooled Fe-Cr-Ni alloys. Part 3: Phase selection in chill casting
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering
In Parts 1 and 2 of this series of articles, it was shown that a range of levitation-melted Fe-Cr-Ni alloys, both hypoeutectic and hypereutectic, all solidified with the hypereutectic phase (bcc) as their primary phase, except for the hypoeutectic alloys at low undercoolings. In this article, the effect of heat extraction on phase formation is studied by chill casting the undercooled alloys before nucleation. Two of the previously studied alloys are examined; one hypoeutectic and the other hypereutectic. Chill substrates employed were copper, stainless steel, alumina, zirconia, and a liquid gallium-indium bath. Contrary to the case of levitation melting and solidification, it is found that the dominant primary phase to solidify in both alloys, independent of chill substrate, is the hypoeutectic phase (fcc). It is concluded that chilling the undercooled melt results in nearly concurrent nucleation of bcc and fcc. Two different mechanisms are considered as possible explanations of the subsequent fcc phase selection during growth. These are termed growth velocity and phase stability mechanisms. Evidence favors a phase stability mechanism, in which the bcc phase massively transforms to fcc early in solidification to that fcc then grows without competition. It is suggested that this mechanism may also explain structures observed in welds and other rapid solidification processes.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 556480
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 11 Vol. 28; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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