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Effects of nitride precipitation on delta phase formation in additively manufactured nickel superalloys

Published

Author(s)

James Zuback, Todd Palmer

Abstract

Additively manufactured Inconel 625 is particularly susceptible to the formation of niobium-rich δ-phase precipitates in the interdendritic regions during high temperature exposure. With specific minor alloying element combinations combined with nitrogen mass fractions on the order of 0.1 %, the formation of δ-phase can be suppressed through the precipitation of secondary phases. For example, mass fractions of 0.39 % silicon and 0.03 % titanium led to the precipitation of Z-phase and η-nitrides, which consumed the excess niobium in the interdendritic regions and limited δ-phase formation. Even when holding the material at a temperature of 870 °C for 1000 h, the δ-phase volume fraction was approximately 2 %, which is far below the 6 % level observed in the wrought condition. When the titanium mass fraction was increased to 0.21 % and the silicon mass fraction decreased to 0.05 %, titanium-rich MN nitrides formed within the interdendritic regions instead. Since much of the Nb in these regions was not consumed by the nitrides, δ-phase formation was promoted and reached volume fractions above 10 %. The addition of a hot isostatic pressing step prior to high temperature exposure in both alloys produced a more uniform niobium distribution and minimized δ-phase formation at shorter times. At extended times, trends in the δ-phase volume fractions were similar to those observed in the as-deposited condition, with the initial alloy compositions driving differences in the distribution of excess niobium available for δ-phase formation.
Citation
Journal of Alloys and Compounds
Volume
976

Keywords

Additive manufacturing, Nickel superalloy, X-ray diffraction (XRD), Phase transformations, Precipitates

Citation

Zuback, J. and Palmer, T. (2023), Effects of nitride precipitation on delta phase formation in additively manufactured nickel superalloys, Journal of Alloys and Compounds, [online], https://doi.org/10.1016/j.jallcom.2023.172936, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956296 (Accessed June 14, 2024)

Issues

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Created December 1, 2023