Hot Corrosion-Protected Gas Turbine Disk Coating System
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Solution Overview
Problem
Gas turbine components, particularly high-pressure compressor and turbine disks, face significant challenges with hot corrosion due to increasing operating temperatures and exposure to particulate matter and SO2, leading to durability risks and inadequate hot corrosion resistance in polycrystalline Ni-base superalloys, necessitating improved coatings that also minimize low cycle fatigue.
Innovation Solution
A coating system comprising a nickel-based first layer and a chromium-based second layer, applied through plating and electroplating respectively, is used on a nickel-based superalloy substrate, providing a ductile interface and corrosion resistance without a ceramic layer, with specific thickness ranges for each layer to prevent crack propagation and enhance protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a ceramic thermal barrier coating is applied, then thermal insulation is improved, but hot corrosion resistance deteriorates
Solution Approach 1:
The coating system is segmented into multiple functional layers: a ceramic thermal barrier coating layer for thermal insulation, a metallic bond coat layer for corrosion protection, and a superalloy substrate for structural integrity. This segmentation allows each layer to perform its specialized function without compromising the others.
Solution Approach 2:
The patent employs a composite coating system combining ceramic and metallic materials. The ceramic layer (e.g., YSZ - yttria stabilized zirconia) provides thermal insulation, while the metallic bond coat layer (e.g., MCrAlY alloy) provides hot corrosion resistance. This composite structure resolves the contradiction by integrating materials with complementary properties.
2Power
If operating temperature is increased, then power output is improved, but hot corrosion resistance deteriorates
Solution Approach 1:
The coating system is applied to the disk surface before the disk is exposed to high-temperature operation. The metallic bond coat layer is pre-applied to create a protective barrier that prevents hot corrosion from initiating during high-power operation, allowing the disk to operate at elevated temperatures without suffering from corrosion damage.
Solution Approach 2:
The patent modifies the chemical composition and microstructure of the coating layers to withstand high-temperature operation. The metallic bond coat contains aluminum and other elements that form protective oxide scales at high temperatures, changing the surface chemistry to resist hot corrosion while maintaining the bulk material's high-temperature strength for power generation.
3Reliability
If a thick metallic coating is applied for corrosion protection, then hot corrosion resistance is improved, but low cycle fatigue deteriorates
Solution Approach 1:
The coating system applies different thicknesses and compositions to different regions of the disk surface. The metallic bond coat is applied where corrosion protection is needed, while maintaining controlled thickness to avoid excessive stress. The coating properties are locally optimized to provide corrosion protection without compromising the overall fatigue performance of the disk.
Solution Approach 2:
The patent carefully controls the thickness, composition, and microstructure of the metallic bond coat layer. By optimizing these parameters, the coating provides sufficient hot corrosion resistance while maintaining ductility and minimizing adverse effects on low cycle fatigue performance. The superalloy substrate composition is also adjusted to balance strength and ductility.
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 system effectively enhances hot corrosion resistance and reduces low cycle fatigue, ensuring the durability of gas turbine components by preventing crack propagation and offering improved surface protection, suitable for use in high-temperature environments.
Implementation Method 1
A coating system has a nickel-based first layer and a chromium-based second layer, each having a characteristic thickness, wherein the first layer is essentially pure nickel and the second layer is essentially pure chromium applied through plating and electroplating
Implementation Method 2
A coating system has a nickel-based first layer and a chromium-based second layer, each having a characteristic thickness, wherein the first layer is essentially pure nickel and the second layer is essentially pure chromium applied through plating and electroplating
Data Source
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AI summary
A coated article (22) comprises a substrate (100) and a coating system (102) atop the substrate. The coating system has a nickel-based first layer (104) and a chromium-based second layer (108) atop the first layer.