Rare Earth Silicate Coating Phase Stability
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Solution Overview
Problem
Rare earth silicate coatings for high-temperature applications, such as aircraft engines and gas turbines, face issues with phase transformation and thermal stress due to high costs and non-uniform distribution of rare earth elements, leading to coating damage and instability.
Innovation Solution
A coated member with a bond coat and a top coat comprising a mixed phase of rare earth disilicate and monosilicate, where the rare earth disilicate is a solid solution of Y1-aLn1a)2Si2O7 or (Y1-cLn2c)2Si2O7, and the monosilicate is Y2SiO5, with specific composition ratios to prevent phase transformation and adjust thermal expansion coefficients, ensuring stability and steam resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Y2Si2O7 is used as a coating material to reduce cost and match thermal expansion coefficients, then manufacturing cost is reduced and thermal stress is alleviated, but phase transformation occurs at high temperature causing coating damage
Solution Approach 1:
The invention uses a composite coating structure with a bond coat layer and a top coat layer. The top coat layer contains a mixture of rare earth disilicate (providing phase stability) and rare earth monosilicate (providing steam resistance). This composite structure combines the advantages of different materials to achieve both cost-effectiveness and high-temperature stability.
Solution Approach 2:
The invention changes the chemical composition parameters of the coating by introducing a specific ratio of rare earth monosilicate to rare earth disilicate. This parameter adjustment prevents the phase transformation that occurs in pure Y2Si2O7 at high temperatures, thereby maintaining coating stability while controlling costs.
2Reliability
If pure rare earth disilicate is used to prevent phase transformation, then coating stability is improved, but manufacturing cost increases significantly
Solution Approach 1:
The invention applies local quality by creating a top coat layer with specific compositional characteristics that differ from the bond coat layer. The top coat contains a controlled mixture of rare earth disilicate and monosilicate, providing localized phase stability and steam resistance where needed, while the bond coat provides substrate protection.
Solution Approach 2:
The invention optimizes the composition parameters by using a specific ratio of rare earth monosilicate to rare earth disilicate in the top coat layer. This parameter optimization maintains phase stability while significantly reducing the amount of expensive rare earth disilicate required, thereby lowering manufacturing costs.
3Ease of manufacture
If heterogeneous mixing of rare earth disilicates is used, then manufacturing simplicity is maintained, but phase stability is insufficient due to non-uniform distribution
Solution Approach 1:
The invention applies preliminary action by pre-forming the top coat layer with a controlled mixture of rare earth monosilicate and disilicate before the component enters service. This preliminary structuring ensures uniform distribution of phases and stable microstructure, preventing non-uniform degradation during high-temperature operation.
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 solution prevents coating damage from phase transformation and thermal stress, extends the lifespan of the coating film, and reduces material costs by stabilizing the phase and adjusting thermal expansion coefficients, making it suitable for high-temperature environments.
Implementation Method 1
phase transformation of Y2Si2O7 (γ→β) accompanied with a volume change can occur in the vicinity of 1300° C.
Implementation Method 2
A thermal expansion coefficient of Y2Si2O7 is 3.7×10−6/K and is close to a thermal expansion coefficient (3.5×10−6/K to 4.5×10−6/K) of a SiC fiber-reinforced SiC matrix composite.
Implementation Method 3
a bond coat and a top coat which are sequentially laminated on a substrate
Data Source
AI summary
Provided are a coated member in which damage of a coating film can be suppressed in a high temperature environment and the coating may be performed at low cost, and a method of manufacturing the same. A coated member includes a bond coat and a top coat sequentially laminated on a substrate made of a Si-based ceramic or a SiC fiber-reinforced SiC matrix composite, wherein the top coat includes a layer composed of a mixed phase of a (Y1-aLn1a)2Si2O7 solid solution (here, Ln1 is any one of Nd, Sm, Eu, and Gd) and Y2SiO5 or a (Y1-bLn1′b)2SiO5 solid solution (here, Ln1′ is any one of Nd, Sm, Eu, and Gd), or a mixed phase of a (Y1-cLn2c)2Si2O7 solid solution (here, Ln2 is any one of Sc, Yb, and Lu) and Y2SiO5 or a (Y1-dLn2′d)2SiO5 solid solution (here, Ln2′ is any one of Sc, Yb, and Lu).