Rare Earth Disilicate Intermediate Coating for TGO Thickness Control
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Solution Overview
Problem
Ceramic and ceramic matrix composite materials used in high-temperature mechanical systems can react with water vapor, leading to material recession and reduced mechanical properties, necessitating the use of environmental barrier coatings (EBCs) to protect against oxidative environments, but these coatings often suffer from spallation or delamination due to microstructural flaws and TGO layer thickness issues.
Innovation Solution
An intermediate coating system is introduced, comprising a silicon-based bond coat and a rare earth monosilicate or oxide reactive layer that converts silicon dioxide into a rare earth disilicate, reducing the thickness and formation rate of the thermally grown oxide (TGO) layer, thereby enhancing oxidation resistance and adhesion between the EBC and substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an environmental barrier coating is applied to protect ceramic or CMC materials from water vapor and oxidation, then oxidation resistance is improved, but spallation or delamination occurs due to TGO layer thickness issues
Solution Approach 1:
A reactive layer containing rare earth monosilicate or rare earth oxide is introduced as an intermediary between the bond coat and the EBC. This reactive layer reacts with silicon dioxide from the bond coat to form a converted layer of rare earth disilicate, which serves as a mediator that reduces TGO layer thickness and improves interfacial compatibility between the bond coat and EBC, thereby preventing spallation and delamination while maintaining oxidation resistance
Solution Approach 2:
The invention changes the chemical composition parameters of the intermediate coating by incorporating rare earth elements (such as ytterbium, lanthanum, or neodymium) in specific ratios with silicon. This parameter change transforms the reaction products from thick TGO layers to thinner rare earth disilicate layers, fundamentally altering the protection mechanism to achieve both thin TGO thickness and strong adhesion
2Reliability
If a bond coat with silicon is used to form a protective oxide layer, then oxidation resistance is improved, but the TGO layer becomes too thick causing coating failure
Solution Approach 1:
The invention converts the harmful effect of excessive silicon oxidation (which produces thick TGO layers causing coating failure) into a beneficial process by introducing rare earth elements that react with the produced silicon dioxide to form rare earth disilicates. This transformation turns the harmful thick TGO formation into a controlled process that produces thin, protective rare earth disilicate layers instead
Solution Approach 2:
The invention modifies the oxidation reaction parameters by adding rare earth elements to the bond coat composition. This changes the reaction products from pure silicon dioxide (forming thick TGO) to rare earth disilicates (forming thin layers), fundamentally altering the TGO growth mechanism to achieve the desired thin layer thickness while maintaining protection
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 intermediate coating system effectively reduces the likelihood of spallation and delamination, maintains oxidation resistance, and extends the service life of the coating by forming a thinner, more compatible TGO layer, which is chemically and thermally stable with the EBC, thus improving the durability of ceramic and CMC materials in high-temperature environments.
Implementation Method 1
oxidation of at least a portion of the silicon of the bond coat to form silicon dioxide
Implementation Method 2
at least a portion of the rare earth monosilicate or rare earth oxide of the reactive layer is configured to react with at least a portion of the silicon dioxide to form a converted layer that includes a rare earth disilicate
Data Source
AI summary
An article includes a substrate, an intermediate coating on the substrate, and an environmental barrier coating (EBC) on the intermediate coating. The substrate includes a ceramic, ceramic matrix composite (CMC), or superalloy. The EBC includes a rare earth disilicate. When the intermediate coating is at an initial state, such as prior to exposure to an oxidating environment, the intermediate coating includes a bond coat on the substrate and a reactive layer on the bond coat. The bond coat includes silicon, while the reactive layer includes a rare earth monosilicate or rare earth oxide. In response to oxidation of a portion of the silicon of the bond coat to form silicon dioxide, a portion of the rare earth monosilicate or rare earth oxide of the reactive layer is configured to react with at least a portion of the silicon dioxide to form a converted layer that includes a rare earth disilicate.