Key Takeaways & Executive Findings
- •• The corrosion mechanism of nickel-based single-crystal superalloys in mixed Na2SO4/NaCl molten salts at 700 °C involves cyclic oxide layer formation and decomposition, leading to a protective NiO layer with a regenerating Al2O3 barrier. • Alloying elements Cr, Al, Ta, and particularly Re significantly improve thermal corrosion resistance, providing strategic directions for alloy composition design. • Gibbs free energy calculations of corrosion products help elucidate the influence of alloying elements on corrosion performance, enabling predictive insights for material selection. • The findings enhance understanding of low-temperature hot corrosion (600–750 °C) mechanisms, critical for aerospace and energy applications where superalloys face aggressive salt environments.
Abstract
In this investigation, we examined the high-temperature corrosion behavior of three nickel-based single-crystal superalloys subjected to a mixed molten salt environment of Na2SO4 and NaCl at 700 °C, leading to a preliminary elucidation of their molten salt corrosion mechanisms. By further comparing the corrosion degree of the three nickel-based single-crystal superalloys combined with the Gibbs free energy calculation of the corrosion products, the influence of alloying elements on the corrosion performance of nickel-based single-crystal superalloys was analyzed. It was established that the corrosion mechanism of these nickel-based single-crystal superalloys predominantly involves a cyclic process of oxide layer formation and decomposition, ultimately resulting in the establishment of a protective layer principally composed of NiO, with a constantly regenerating Al2O3 barrier, impeding further alloy degradation. Furthermore, the inclusion of elements such as Cr, Al, Ta, and notably Re has been found to markedly improve the thermal corrosion resistance of the superalloys. These insights not only enhance our comprehension of the corrosion mechanisms pertinent to nickel-based superalloys, but also provide strategic directions for alloy composition refinement aimed at bolstering their corrosion resilience.
1. Introduction
Nickel-based single-crystal superalloys are widely used in aerospace and energy applications due to their excellent high-temperature mechanical properties [1, 2]. However, during the application of superalloys [3, 4], working in aggressive environments containing contaminants such as sodium, sulfur, and vanadium makes nickel-based single-crystal superalloys extremely susceptible to thermal corrosion [5, 6]. Therefore, there is an urgent need to study the thermal corrosion behavior of nickel-based single-crystal superalloy materials to provide a basis for the composition design of nickel-based single-crystal superalloys [7−9].
Generally speaking, the corrosion of superalloys in service can be categorized into two forms: high-temperature thermal corrosion and low-temperature thermal corrosion [8, 10]. High-temperature hot corrosion occurs mainly at 900 − 1000 ℃ and low-temperature hot corrosion occurs mainly at 600−750 ℃. Some studies focus on low-temperature hot corrosion at 700 ℃ [11, 12].
Corrosion resistance in nickel-based superalloys, particularly under low-temperature thermal conditions, is governed by a complex interplay of factors. Emerging research highlights the pivotal role of molten salt composition in dictating the corrosion dynamics of these high-temperature materials, which focused on the corrosion behavior of DZ40M and K452 alloys in NaCl molten salt at 700 ℃, emphasizing the influence of specific elements, C, Cr, W, Al and Ti, on their performance. Notably, Cr and Al emerge as critical role in enhancing corrosion resistance, whereas C and W may exacerbate the degradation process [13]. Whereas, relatively high concentrations of Cr, Co and Ti elements provide superalloys with better corrosion resistance to S and Cl elements [14].
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LI Qian-yi, LIU Feng, WANG Zi, ZHAO Yun-xing, TAN Li-ming, HUANG Lan (2025). Corrosion behavior of three nickel-based single-crystal superalloys in mixed Na2SO4 and NaCl molten salts at 700 ℃. Journal of Central South University. https://doi.org/10.1007/s11771-025-6068-2
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Frequently Asked Questions
What is the corrosion mechanism of nickel-based single-crystal superalloys in mixed Na2SO4 and NaCl molten salts at 700 °C?
The corrosion mechanism predominantly involves a cyclic process of oxide layer formation and decomposition, ultimately resulting in a protective layer principally composed of NiO, with a constantly regenerating Al2O3 barrier that impedes further alloy degradation.
Which alloying elements improve the thermal corrosion resistance of nickel-based single-crystal superalloys?
The inclusion of elements such as Cr, Al, Ta, and notably Re has been found to markedly improve the thermal corrosion resistance of the superalloys.
Why is the study of low-temperature hot corrosion at 700 °C important?
Low-temperature hot corrosion (600–750 °C) is a significant degradation mode for superalloys used in aerospace and energy applications, and understanding it is crucial for alloy composition design to enhance corrosion resilience.
How does the Gibbs free energy calculation contribute to the analysis?
Gibbs free energy calculations of corrosion products help compare the corrosion degree of the alloys and analyze the influence of alloying elements on corrosion performance, providing a thermodynamic basis for the observed behavior.
What are the practical implications of this research?
The insights enhance comprehension of corrosion mechanisms in nickel-based superalloys and provide strategic directions for alloy composition refinement aimed at bolstering corrosion resilience in aggressive molten salt environments.
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