Halo Formation During Solidification of Refractory Metal Aluminide Ternary Systems

The evolution of eutectic morphologies following primary solidification has been studied in the refractory metal aluminide (Ta-Al-Fe, Nb-Al-Co, and Nb-Al-Fe) ternary systems. The undercooling accompanying solid growth, as related to the extended solute solubility in the primary and secondary phases...

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Bibliographic Details
Published in:Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2018-05, Vol.49 (5), p.1749-1761
Main Authors: D’Souza, N., Feitosa, L. M., West, G. D., Dong, H. B.
Format: Article
Language:English
Subjects:
Aluminides
Aluminum
Characterization and Evaluation of Materials
Chemistry and Materials Science
Cobalt
Equilibrium
Intermetallic compounds
Iron
Materials Science
Metallic Materials
Metallurgy
Mu phase
Nanotechnology
Niobium
Nucleation
Solidification
Solidus
Solubility
Structural Materials
Supercooling
Surfaces and Interfaces
Tantalum
Ternary systems
Thin Films
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Summary:The evolution of eutectic morphologies following primary solidification has been studied in the refractory metal aluminide (Ta-Al-Fe, Nb-Al-Co, and Nb-Al-Fe) ternary systems. The undercooling accompanying solid growth, as related to the extended solute solubility in the primary and secondary phases can be used to account for the evolution of phase morphologies during ternary eutectic solidification. For small undercooling, the conditions of interfacial equilibrium remain valid, while in the case of significant undercooling when nucleation constraints occur, there is a departure from equilibrium leading to unexpected phases. In Ta-Al-Fe, an extended solubility of Fe in σ was observed, which was consistent with the formation of a halo of μ phase on primary σ. In Nb-Al-Co, a halo of C14 is formed on primary CoAl, but very limited vice versa. However, in the absence of a solidus projection it was not possible to definitively determine the extended solute solubility in the primary phase. In Nb-Al-Fe when nucleation constraints arise, the inability to initiate coupled growth of NbAl 3  + C14 leads to the occurrence of a two-phase halo of C14 + Nb 2 Al, indicating a large undercooling and departure from equilibrium.
ISSN:1073-5623
1543-1940
DOI:10.1007/s11661-018-4519-1