I-Phase Al Coating for Gas Turbine Corrosion
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Solution Overview
Problem
Aluminum-based abradable coatings in gas turbine engines experience corrosion and spallation issues, leading to mechanical failures and blade wear due to galvanic interactions with bondcoats, particularly in the cold section where temperature is lower.
Innovation Solution
A metallic matrix coating comprising Al, Cr, Mn, Co, and Zr with an icosahedral phase (I-phase) is used, which mitigates corrosion by forming a self-passivating layer, combined with a filler like hBN and porosity to reduce mechanical failures and spallation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If aluminum-based abradable coatings are used in cold section gas turbine engines, then the coatings provide abradability and compliance for blade tip clearance control, but the coatings suffer from corrosion and spallation due to galvanic interactions with bondcoats
Solution Approach 1:
The invention changes the chemical composition parameters of the aluminum-based coating by adding specific amounts of Cr (3-6 wt%), Mn (1-4 wt%), Co (0.1-3.5 wt%), and Zr (0.3-2.0 wt%). This compositional modification transforms the coating's electrochemical properties, making it more noble than traditional Al-Si coatings and reducing galvanic corrosion susceptibility while maintaining abradability.
Solution Approach 2:
The invention creates a composite coating system consisting of the modified aluminum-based alloy coating combined with a nickel-chromium-aluminum-yttrium bondcoat. This composite structure provides both abradability from the aluminum-based coating and corrosion resistance through the protective bondcoat layer, resolving the contradiction between ease of operation and reliability.
2Ease of operation
If traditional Al-Si coatings with polyester binder are used, then the coatings achieve abradability through polymer fugitive behavior, but the coatings experience mechanical failures and spallation
Solution Approach 1:
The invention replaces the polyester binder (which burns off during operation) with inexpensive porosity-forming particles such as glass beads, ceramic particles, or salt particles. These particles create controlled porosity in the coating, providing abradability without the mechanical weakness and spallation issues associated with organic binders.
Solution Approach 2:
The invention incorporates porosity-forming particles that create a porous structure in the coating after application and binder removal. This porous structure provides the necessary compliance and abradability while the metallic matrix maintains mechanical integrity, preventing spallation.
3Reliability
If the coating composition is modified to improve corrosion resistance, then the coating forms protective oxide layers, but the coating may lose abradability and compliance
Solution Approach 1:
The invention applies local quality by creating a dual-function coating structure: the metallic matrix (Al-Cr-Mn-Co-Zr) provides corrosion resistance through protective oxide formation, while the embedded porosity-forming particles and controlled porosity (10-50% volume fraction) provide abradability and compliance. Each component performs its specific function locally within the coating system.
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 I-phase alloy matrix coating reduces mechanical failures and spallation by limiting oxide and corrosion product generation, enhancing the durability and integrity of the abradable layer, thereby minimizing blade wear and tip clearance issues.
Implementation Method 1
the Al-Si abradable layer forms a self-passivating layer that mitigates corrosion and limits oxide generation
Implementation Method 2
corrosion and spallation issues, leading to mechanical failures and blade wear due to galvanic interactions with bondcoats
Data Source
Figure 1
Figure 2
Figure 2A~2B
AI summary
A coated article comprising: a substrate; and a coating on the substrate comprising: a metallic matrix comprising, by weight: Al as a largest constituent; 1.9-6.0 Cr; 1.0-4.0 Mn; 0.1-3.5 Co; and 0.2-2.0 Zr; and a filler and optionally porosity.