Rare Earth Silicate Barrier Coating for Crack-Free Plasma Spray
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Solution Overview
Problem
Existing methods for depositing ytterbium silicate environmental barrier coatings on ceramic matrix composites face challenges such as high amorphous phase formation, thermal stress-induced cracking, and porosity issues, which compromise the durability and efficiency of gas turbine components.
Innovation Solution
A coating comprising a rare earth monosilicate and disilicate with a specific weight ratio, deposited using atmospheric plasma spraying at elevated substrate temperatures and controlled plasma torch power, ensuring high crystallinity, controlled porosity, and absence of through-thickness cracks, without the need for additional heat treatment or vacuum chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional atmospheric plasma spray is used to deposit ytterbium silicate coatings, then the coating formation is simple and cost-effective, but the coating becomes amorphous with high porosity and contains cracks, reducing its protective performance
Solution Approach 1:
The patent changes the substrate temperature parameter to above the glass-formation temperature of silicates (approximately 1000°C) during the plasma spray process. This temperature parameter change enables the coating to crystallize in-situ, transforming it from amorphous to crystalline structure, which eliminates cracks and improves protective performance while maintaining the simplicity of atmospheric plasma spray deposition
Solution Approach 2:
The patent utilizes the phase transition from amorphous to crystalline state by controlling the substrate temperature above the glass-formation temperature during deposition. This phase transition occurs in-situ during the spray process, allowing the coating to form with crystalline structure directly, eliminating the need for post-deposition heat treatment and vacuum chambers
2Reliability
If very low-pressure plasma spray is used to achieve highly crystalline coatings, then the coating crystallinity and protective performance are improved, but the process requires large vacuum chambers and complex setup, increasing device complexity and cost
Solution Approach 1:
The patent extracts the crystallization function from the vacuum environment and implements it through temperature control in atmospheric pressure. By removing the requirement for vacuum chambers and complex VLPPS setup, while maintaining crystalline coating formation through substrate temperature control above the glass-formation temperature, the process becomes simpler and more cost-effective for industrial applications
Solution Approach 2:
The patent replaces the mechanical/vacuum-based crystallization method (VLPPS requiring vacuum chambers) with a thermal field-based method. By using substrate temperature control above the glass-formation temperature during atmospheric plasma spray, the crystallization process is achieved through thermal energy rather than vacuum mechanical systems, eliminating complex equipment requirements
3Reliability
If substrate temperature is kept above glass-formation temperature during spraying to boost crystallinity, then the coating crystallinity improves, but the process requires additional heating equipment and energy, increasing process complexity and cost
Solution Approach 1:
The patent merges the heating function with the plasma spray process itself. The plasma torch provides both the deposition energy and the substrate heating to above glass-formation temperature simultaneously. This integration eliminates the need for separate heating equipment, as the plasma spray process naturally achieves the required temperature range for in-situ crystallization
Solution Approach 2:
The plasma spray process is made multi-functional, serving both as the deposition method and as the heating source for crystallization. By controlling the plasma parameters and substrate temperature above the glass-formation temperature, the same process achieves both coating formation and crystallization, eliminating additional equipment requirements
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 achieves a highly crystalline, crack-free, and uniformly porous coating that enhances the durability and thermal cyclic performance of ceramic matrix composites, reducing costs and improving adhesion to SiC substrates, while maintaining efficient deposition efficiency.
Implementation Method 1
depositing the coating by atmospheric plasma spraying a coating precursor on the heated substrate
Implementation Method 2
the coating is at least 60% crystalline
Data Source
AI summary
We provide a coating as an environmental barrier coating, for example on a ceramic matrix composite, e.g., in a gas turbine. The coating comprises a rare earth monosilicate and a rare earth disilicate in a weight ratio of at least about 70:30. The coating is at least 60% crystalline, has a porosity of at most about 40%, and is free of through-thickness cracks. We also provide a method of manufacturing this coating comprising heating a substrate to at least about 500° C., and depositing the coating by atmospheric plasma spraying ytterbium disilicate particles on the heated substrate, wherein the atmospheric plasma spraying is performed with a plasma spray torch operated at an operating power of at least 60 kW.