CMAS-Resistant Overlay Coating With Diffusion Barrier Structure
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Solution Overview
Problem
Conventional thermal barrier coatings in gas turbines are susceptible to degradation from calcium-magnesium-alumino-silicate (CMAS) deposits, leading to delamination and reduced durability, and existing CMAS reactive coatings are costly and inefficient due to the use of rare earth metals.
Innovation Solution
A CMAS resistant overlay coating with a metal oxide matrix containing aluminum and chromium, formed through cathodic arc evaporation, which diffuses non-oxidized metallic constituents to form an impermeable barrier layer at high temperatures, inhibiting CMAS infiltration and degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional thermal barrier coatings (YSZ-based) are used to provide thermal insulation, then low thermal conductivity is achieved, but the coatings become susceptible to CMAS infiltration and chemical dissolution leading to delamination
Solution Approach 1:
The patent applies composite materials by combining aluminum oxide (Al2O3) and chromium oxide (Cr2O3) in a layered structure. The Al2O3 layer provides thermal insulation similar to YSZ, while the Cr2O3 layer specifically resists CMAS infiltration and chemical dissolution. This composite approach allows the coating to simultaneously achieve low thermal conductivity and high resistance to CMAS corrosion without using rare earth metals.
Solution Approach 2:
The patent implements local quality by creating distinct functional layers with different properties. The Al2O3 layer is optimized for thermal insulation with low thermal conductivity, while the Cr2O3 layer is positioned at the outer surface specifically to resist CMAS attack. Each layer performs its specialized function locally, with the Cr2O3 layer forming a protective barrier against CMAS infiltration while the Al2O3 layer provides the thermal barrier function.
2Reliability
If CMAS reactive thermal barrier coatings based on rare earth zirconates are applied to resist CMAS infiltration, then CMAS resistance is improved, but the coating toughness decreases and production costs increase
Solution Approach 1:
The patent replaces expensive rare earth metals (gadolinium, ytterbium, samarium) with more economical aluminum and chromium materials. The Cr2O3 layer provides the necessary CMAS resistance function without requiring costly rare earth zirconates. This substitution significantly reduces material costs while maintaining adequate CMAS resistance through the chromium oxide layer's inherent properties of forming stable, dense structures that block CMAS infiltration.
Solution Approach 2:
The patent changes the material composition parameters from rare earth-based zirconates to aluminum oxide and chromium oxide. This parameter change fundamentally alters the coating's chemical composition and structure, achieving CMAS resistance through different mechanisms - specifically through Cr2O3's ability to form a dense, stable outer layer that resists chemical dissolution and physical infiltration by CMAS, while maintaining coating toughness through the metallic oxide system.
3Reliability
If CMAS reactive thermal barrier coatings are applied to prevent CMAS infiltration, then CMAS resistance is improved, but production costs increase due to rare earth metal usage
Solution Approach 1:
The patent substitutes expensive rare earth metals with more economical aluminum and chromium materials. The Cr2O3 layer provides the necessary CMAS resistance function without requiring costly rare earth zirconates. This substitution significantly reduces material costs while maintaining adequate CMAS resistance through the chromium oxide layer's inherent properties of forming stable, dense structures that block CMAS infiltration.
4Power
If the operating temperature of gas turbines is increased to enhance efficiency, then turbine efficiency is improved, but CMAS deposits melt and attack the thermal barrier coating more aggressively
Solution Approach 1:
The patent converts the harmful effect of high temperature into a beneficial protective mechanism. The Cr2O3 layer is specifically designed to remain stable and resistant to CMAS attack at elevated temperatures. When CMAS contacts the Cr2O3 layer at high operating temperatures, the chromium oxide forms a stable, dense structure that actively resists chemical dissolution and physical infiltration, transforming the high-temperature environment from a threat into a condition where the protective layer's properties are optimized.
Solution Approach 2:
The patent applies composite materials by combining aluminum oxide (Al2O3) and chromium oxide (Cr2O3) in a layered structure. The Al2O3 layer provides thermal insulation similar to YSZ, while the Cr2O3 layer specifically resists CMAS infiltration and chemical dissolution. This composite approach allows the coating to simultaneously achieve low thermal conductivity and high resistance to CMAS corrosion without using rare earth metals.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coating provides excellent mechanical stability and adherence to underlying layers, even at high temperatures, effectively preventing CMAS infiltration and degradation, while being cost-effective and versatile.
Implementation Method 1
a cathodic arc evaporation (CAE) process for forming such a CMAS resistant overlay coating
Implementation Method 2
which diffuses non-oxidized metallic constituents to form an impermeable barrier layer at high temperatures
Data Source
AI summary
A CMAS resistant overlay coating including at least one CMAS resistant layer, wherein the overlay coating is i. disposed over a surface of a substrate including a material susceptible to CMAS corrosion, ii. includes a metal oxide matrix and iii. has at least partially a vertical columnar structure. Moreover, at least one non-oxidized metallic constituent selected from the group of aluminum, chromium and metallic constituents including aluminum and chromium is embedded in the metal oxide matrix. Furthermore, a substrate has a CMAS resistant overlay coating at issue on a surface of a material susceptible to CMAS corrosion. A CAE process is provided for forming such a CMAS resistant overlay coating on a surface of a material susceptible to CMAS corrosion.