Key Takeaways & Executive Findings
- •• The melting sequence of CMAS and NaCl significantly influences the failure mode of YSZ thermal barrier coatings, with mixed corrosion and NaCl-first melting leading to buckling failure, while CMAS-first melting results in spalling failure. • Experimental and finite element simulations reveal that the corrosion mechanisms are governed by the infiltration and reaction of molten salts, affecting the strain tolerance and phase stability of the coating. • The presence of NaCl accelerates the degradation of the bonding coating and promotes the formation of brittle spinel oxides, exacerbating TBC failure. • This study provides critical data for optimizing TBC systems to withstand complex corrosive environments, particularly in marine and high-temperature applications.
Abstract
Calcium–magnesium–alumina–silicate (CMAS) and/or molten salt corrosion have attracted increased attention, which is an important cause of thermal barrier coating (TBC) failure. In this study, the effect of CMAS and NaCl melting sequence on the corrosion mechanisms of yttria-stabilized zirconia (YSZ) TBCs was revealed through experiments and finite element simulations. The YSZ TBCs were prepared via atmospheric plasma spraying. Subsequently, the CMAS and NaCl corrosion experiments of the TBCs were conducted at 1250°C. Results indicated that the melting sequence of CMAS and NaCl could influence the TBC failure mode. The coating failure modes after CMAS + NaCl mixed corrosion and NaCl melting followed by CMAS melting were buckling failures. Conversely, the coating failure mode was observed to be spalling failures. This study provides data support for the optimization of TBC systems in complex corrosive environments.
1. Introduction
The turbine inlet temperature is continuously increased to improve the thrust-to-weight ratio of aero-engines. Relying solely on superalloys cannot sufficiently satisfy the requirements of aero-engines. Thermal barrier coatings (TBCs), blade cooling design, and single-crystal superalloy material technology are three core technologies for advanced aero-engine blades. The TBC system consists of top ceramic coating (TC), thermally grown oxides (TGO), bonding coating (BC), and substrate (SUB). Currently, the most common TC material is yttria-stabilized zirconia (YSZ), which has a high thermal expansion coefficient (~11 × 10−6 K−1), high melting point (~2700°C), and low thermal conductivity (~2 W·m–1·K−1) [1–4].
Nevertheless, during aircraft operation, debris in the runway, as well as fly ash, sand, and volcanic ash in the air, will inevitably deposit on TBC surfaces; these deposits are referred to as calcium–magnesium–alumina–silicate (CMAS) [5–7]. When service temperature exceeds the melting temperature of CMAS, which is generally approximately 1230°C, CMAS will penetrate the interior of YSZ coating through defects, such as microcracks and pores, reducing the strain tolerance of the TBC system during cooling [8–10]. Meanwhile, CMAS reacts with the stabilizer Y2O3 in YSZ, forming a monoclinic phase (m-ZrO2) and causing a destructive phase transformation of YSZ [8,11–12]. The TBC system becomes prone to delamination during service due to thermal–mechanical–chemical damage [10,13–14].
Additionally, because salt is mostly abundant in the atmosphere near oceans and coasts, aircraft are exposed to high humidity and salinity (specifically NaCl), especially carrier-based aircraft that frequently take off and land on the sea surface. Consequently, TBCs encounter the challenge of thermal corrosion in aero-engines operating in marine environments [15–16]. Furthermore, some studies have indicated that the presence of NaCl accelerates BC degradation and generates complex brittle spinel oxides, leading to TBC system failure [15,17–19].
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Yang Feng, Yong Shang, Chun Li, Xiao Zhang, Yanling Pei, Shengkai Gong, Huibin Xu (2025). Effects of calcium–magnesium–alumina–silicate and NaCl melting sequence on corrosion resistance of thermal barrier coatings. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3017-2
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Frequently Asked Questions
What is the effect of CMAS and NaCl melting sequence on TBC corrosion?
The melting sequence significantly influences the failure mode: mixed corrosion and NaCl-first melting lead to buckling failure, while CMAS-first melting results in spalling failure.
What are the main corrosion mechanisms of YSZ TBCs under CMAS and NaCl?
CMAS infiltrates through pores and reacts with Y2O3, causing phase transformation, while NaCl accelerates bonding coating degradation and forms brittle spinel oxides, both leading to coating failure.
How were the YSZ TBCs prepared in this study?
The YSZ TBCs were prepared via atmospheric plasma spraying.
What temperature were the corrosion experiments conducted at?
The corrosion experiments were conducted at 1250°C.
What is the significance of this study for TBC applications?
It provides data support for optimizing TBC systems to withstand complex corrosive environments, particularly in marine and high-temperature applications.
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