Low Melting Phase EBCs Seal Microstructural Defects
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional environmental barrier coatings (EBCs) on Si-based ceramic matrix composites (CMCs) suffer from porosity and microstructural defects, which accelerate oxidant diffusion and lead to rapid thermally grown oxide (TGO) growth, resulting in coating spallation.
Innovation Solution
The use of a thermal spray material feedstock containing a first powder of low melting temperature materials (less than 1500°C) and a second powder of high melting temperature matrix materials, which are blended, agglomerated, and heat-treated to fill microstructural defects and enhance coating density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional air plasma spray process is used for EBC deposition, then the coating can be applied onto Si-based CMCs, but the coating contains porosity and microstructural defects such as splat boundaries and micro-cracks
Solution Approach 1:
The patent changes the chemical composition parameters of the coating material by incorporating low melting temperature glass phases (such as borosilicate glass) into the EBC material system. This compositional parameter change enables the material to undergo beneficial phase transformations during service, sealing microstructural defects and reducing porosity dynamically.
Solution Approach 2:
The patent utilizes phase transition of low melting temperature glass phases (melting point 600-900°C) during high-temperature exposure. The glass phase melts and flows to fill micro-cracks and porosity, then re-solidifies to form a dense, crack-free coating structure, effectively sealing the microstructural defects introduced during APS deposition.
2Device complexity
If conventional EBCs with porosity and microstructural defects are used, then the coating structure is simpler, but oxidant diffusion path is accelerated leading to rapid TGO growth
Solution Approach 1:
The patent modifies the chemical composition by adding reactive elements (such as Al, Si, B) and low melting temperature glass formers to the conventional EBC material system. This compositional parameter change creates a more complex but functionally superior coating that actively responds to oxidation environments by forming protective barriers.
Solution Approach 2:
The patent implements self-service through reactive elements that automatically form protective alumina or silica scales in oxidation environments, and low melting temperature glass phases that self-seal micro-cracks and porosity through melting and flow, without requiring external intervention or complex multi-layer structures.
3Reliability
If low melting temperature materials are added to thermal spray feedstock, then microstructural defects are reduced and TGO growth rate decreases, but the feedstock composition becomes more complex
Solution Approach 1:
The patent creates a composite thermal spray feedstock system combining conventional EBC materials (such as Yb2Si2O7, Gd2SiO5) with low melting temperature glass phases (borosilicate glass) and reactive elements. This composite material approach leverages the complementary properties of each component: the high-temperature stability of rare earth silicates, the crack-healing capability of low melting glass, and the oxidation protection of reactive elements.
Solution Approach 2:
The patent optimizes the compositional parameters of the composite feedstock, controlling the weight percentages of different components (typically 5-20 wt% low melting glass phase, 1-5 wt% reactive elements, balance conventional EBC material) to achieve the desired balance between durability enhancement and processability.
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
This approach results in EBCs with significantly reduced microstructural defects, providing a more than two times slower TGO growth rate compared to coatings without low melting temperature materials, thereby enhancing the durability and environmental protection of CMCs.
Implementation Method 1
a thermal spray material feedstock containing low melting temperature materials in-situ melt, diffuse, and fill EBCs microstructural defects during high temperature coating conditions
Implementation Method 2
low melting temperature materials in-situ melt, diffuse, and fill EBCs microstructural defects
Implementation Method 3
EBCs containing low melting temperature materials provide an enhanced barrier against oxidant (water vapor and oxygen) diffusion
Implementation Method 4
the Si-bond coat will also be oxidized to form a thermally grown oxide (TGO) SiO2 layer
Data Source
AI summary
Environmental barrier materials and coatings containing low melting temperature materials are provided. The materials and coatings include high melting temperature materials, such as rare earth silicates, mullite, hafnon, zircon, HfO2, and rare earth stabilized ZrO2. The low melting temperature materials have a melting temperature of less than 1500° C. The low melting temperature materials in the coating in-situ melt, flow, and fill the microstructural defects after post-heat treatment. Due to reduced microstructural defects, EBCs containing low melting temperature materials provide an enhanced barrier against oxidants diffusion and result in 10 times slower TGO growth rate as compared to coatings without low melting temperature materials.