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Influence of Al/Ti Ratio and Ta Concentration on the As-Cast Microstructure, Phase Composition, and Phase Transformation Temperatures of Lost-Wax Ni-Based Superalloy Castings.

Authors :
Grudzień-Rakoczy, Małgorzata
Rakoczy, Łukasz
Cygan, Rafał
Chrzan, Konrad
Milkovič, Ondrej
Pirowski, Zenon
Source :
Materials (1996-1944). May2022, Vol. 15 Issue 9, p3296-3296. 26p.
Publication Year :
2022

Abstract

The as-cast microstructure, alloying element segregation, solidification behavior, and thermal stability of model superalloys based on Inconel 740 with various Al/Ti ratios (0.7, 1.5, 3.4) and Ta (2.0, 3.0, 4.0 wt%) concentrations were investigated via ThermoCalc simulations, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, dilatometry, and differential scanning calorimetry. The solidification of the superalloys began with the formation of primary γ dendrites, followed by MC carbides. The type of subsequently formed phases depended on the superalloys' initial Al/Ti ratio and Ta concentration. The results obtained from solidification simulations were compared to the obtained microstructures. For all castings, the dendritic regions consisted of fine γ′ precipitates, with their size mainly depending on the initial Al/Ti ratio, whereas in the interdendritic spaces, (Nb, Ta, Ti)C carbides and Nb-rich Laves phase precipitates were present. In high Al/Ti ratio superalloys, β-NiAl precipitates, strengthened by η and α-Cr phases, were observed. Based on dilatometric results, the dissolution of γ′ precipitates was accompanied by a substantial increase in the coefficient of thermal expansion. The end of the dilatation effect took place around the γ′ solvus temperature, as determined via calorimetry. Moreover, the bulk solidus temperature was preceded by the dissolution of the Laves phase, which may be accompanied by local melting. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
19961944
Volume :
15
Issue :
9
Database :
Academic Search Index
Journal :
Materials (1996-1944)
Publication Type :
Academic Journal
Accession number :
156873869
Full Text :
https://doi.org/10.3390/ma15093296