Segmented Environmental Barrier Coating for Thermal Stress Relief
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Solution Overview
Problem
Thick, continuous environmental barrier coatings on ceramic matrix composites in gas turbine engines accumulate thermal stress, leading to cracking and delamination, which compromises their protective effectiveness.
Innovation Solution
A coating design featuring a continuous inner layer with low porosity and a segmented outer layer composed of growth domains and boundaries, where the outer layer is made of partially melted and solidified particles, allowing for differential expansion and reducing thermal stress, thereby maintaining a hermetic seal and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick, continuous environmental barrier coating is applied to protect ceramic matrix composites, then the protective effectiveness against oxidation and recession is improved, but the coating accumulates substantial thermal stress leading to cracking and delamination
Solution Approach 1:
The outer layer is segmented into multiple growth domains separated by domain boundaries. These boundaries act as stress relief zones that accommodate thermal expansion differences between the coating and substrate, preventing the accumulation of substantial thermal stress that would otherwise cause cracking and delamination in continuous coatings.
Solution Approach 2:
Different regions of the outer layer have distinct microstructures: growth domains with high coating material density provide protective functionality, while domain boundaries with low coating material density provide stress relief. This local variation in structure allows the coating to simultaneously maintain protection and accommodate thermal stress.
2Reliability
If the coating material density is increased to improve protective performance, then the hermetic seal is enhanced, but the thermal stress and probability of cracking increase
Solution Approach 1:
The coating is divided into growth domains and domain boundaries with different material densities. The high-density growth domains provide hermetic sealing, while the low-density domain boundaries accommodate thermal stress through their compliant microstructure containing partially melted and solidified particles.
Solution Approach 2:
The domain boundaries contain a comparatively low density of coating material with partially melted and solidified particles, creating a microstructure that is less dense and more compliant. This porous-like structure in the boundaries reduces thermal stress while the high-density growth domains maintain the hermetic seal.
3Reliability
If a continuous outer layer is used to maintain hermeticity, then the seal is improved, but the coating becomes more susceptible to cracking under thermal gradients
Solution Approach 1:
The outer layer is segmented into growth domains separated by domain boundaries. This segmentation allows the coating to maintain hermeticity through the high-density growth domains while the low-density domain boundaries provide compliance and stress relief, preventing crack propagation under thermal gradients.
Solution Approach 2:
The outer layer is a composite microstructure combining high-density coating material regions (growth domains) with low-density regions containing partially melted and solidified particles (domain boundaries). This composite structure provides both hermetic sealing and crack resistance.
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 reduces thermal stress, mitigates sustained peak low cycle fatigue, and extends the lifespan of the underlying component by minimizing the probability of cracking and maintaining a continuous, crack-free structure even under temperature gradients and shocks.
Implementation Method 1
the outer layer being a segmented outer layer and comprising a plurality of at least partially melted and solidified particles
Implementation Method 2
allowing for differential expansion and reducing thermal stress
Data Source
AI summary
Methods for preparing an environmental barrier coating and the resulting coating are provided. The methods and products include the incorporation of a continuous ceramic inner layer and a segmented ceramic outer layer on a CMC component. The segmented ceramic outer layer may be formed by thermal spray techniques. The coating is more stable at higher temperatures and provides for a longer lifetime of the coated component.