Al-Poor Overlay Coating Removal via Aluminum Diffusion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Aluminum-poor (less than 12% Al by weight) overlay coatings on gas turbine components are highly resistant to existing selective stripping methods, leading to potential damage during removal due to the need for non-selective methods like strong acids or aggressive mechanical techniques.
Innovation Solution
Diffusing additional aluminum into the Al-poor overlay coatings to increase the aluminum content to 12% or more, making them removable using selective stripping processes with aqueous compositions containing acids like HxAF6, allowing for safe and effective removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aluminum content in overlay coatings is kept low (less than 12% Al by weight) to improve high-temperature creep and stress rupture resistance, then the coating's mechanical performance at high temperature is improved, but the coating becomes highly resistant to selective stripping methods, requiring non-selective removal methods that can damage the substrate
Solution Approach 1:
The patent applies preliminary action by diffusing aluminum into the overlay coating before the stripping process. This pre-treatment increases the aluminum content in the coating to make it susceptible to selective stripping, thereby enabling easy removal without damaging the substrate while maintaining the low-aluminum coating's high-temperature mechanical properties during service
Solution Approach 2:
The patent changes the chemical composition parameter of the coating by diffusing aluminum into the overlay coating. This parameter change (increasing aluminum content) is temporary and reversible, allowing the coating to be easily stripped after service while maintaining the optimal low-aluminum composition for high-temperature performance during operation
2Reliability
If existing selective stripping methods are used on Al-poor overlay coatings, then the substrate is protected from damage, but the coatings cannot be effectively removed due to their high resistance to stripping
Solution Approach 1:
The patent applies preliminary action by performing aluminum diffusion into the coating before stripping. This pre-treatment modifies the coating's chemical composition to enable effective removal by selective stripping methods, thereby achieving both high substrate integrity and efficient coating removal productivity
Solution Approach 2:
The patent uses aluminum diffusion as an intermediary process between the coating and the stripping solution. This intermediary treatment modifies the coating's aluminum content to act as a bridge, making the coating susceptible to selective stripping while maintaining substrate protection
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 increased aluminum content in the overlay coatings renders them susceptible to selective stripping, reducing the risk of substrate damage and enabling efficient removal without compromising the component's integrity.
Implementation Method 1
Diffusing additional aluminum into the Al-poor overlay coatings to increase the aluminum content to 12% or more
Implementation Method 2
contacting the outer surface of the aluminum-infused overlay coating with an aqueous composition to remove the aluminum-infused overlay coating from the substrate. The aqueous composition includes at least one acid having the formula HxAF6
Data Source
AI summary
A method for selectively removing an aluminum-poor overlay coating from a substrate of a component, which as a result of its low aluminum content is highly resistant to a selective stripping solution. The method entails diffusing aluminum into the overlay coating to form an aluminum-infused overlay coating having an increased aluminum level in at least an outer surface thereof. The diffusion step is carried out so that the increased aluminum level is sufficient to render the aluminum-infused overlay coating removable by selective stripping. The outer surface of the aluminum-infused overlay coating is then contacted with an aqueous composition to remove the aluminum-infused overlay coating from the substrate. The aqueous composition includes at least one acid having the formula HxAF6, and/or precursors thereof, wherein A is Si, Ge, Ti, Zr, Al, and/or Ga, and x is from 1 to 6.