Selective Aluminide Coating Removal for Turbine Refurbishment

Solution Overview

Problem

Existing methods for refurbishing diffusion aluminide coatings in gas turbine components result in significant base metal removal, leading to alloy depletion and reduced component life, as they involve complete removal of the coating, which causes wall thickness loss and dimensional distortion.

Innovation Solution

A process that selectively removes the diffusion coating while minimizing base metal loss, using techniques like solution heat treatment and selective removal of the aluminum-infused additive layer, allowing for retention of wall thickness and reducing the risk of chemical attacks and dimensional distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of repair

If complete removal of the diffusion coating is performed using acidic solution, then the coating is fully removed for refurbishment, but significant base metal removal occurs resulting in wall thickness loss and alloy depletion

Engineering Contradiction:

Improvecoating removal capabilityVSAvoidbase metal loss

Core Design Contradiction:

Ease of repairVSLoss of substance

Solution Approach 1:

The diffusion coating is segmented into two distinct zones: an additive layer (rich in aluminum) and an interdiffusion zone (alloyed with aluminum but containing significant base metal). The invention enables selective removal of only the additive layer while preserving the interdiffusion zone, thus achieving coating removal without significant base metal loss.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The removal process exploits the local quality difference between the additive layer and interdiffusion zone. The additive layer has high aluminum content and reacts readily with acid, while the interdiffusion zone has lower aluminum content and reacts slowly. This allows selective removal of the additive layer using mild acidic solutions.

Inventive Principle:

Principle #3Local quality

2Ease of repair

If complete removal of the diffusion coating including interdiffusion zone is performed, then the coating is fully refurbished, but the substrate surface suffers alloy depletion and dimensional distortion

Engineering Contradiction:

Improvecoating refurbishmentVSAvoiddimensional stability

Core Design Contradiction:

Ease of repairVSManufacturing precision

Solution Approach 1:

The diffusion coating is segmented into an additive layer and an interdiffusion zone. The invention enables selective removal of only the additive layer while preserving the interdiffusion zone, thus achieving coating removal without significant base metal loss.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the chemical parameters of the removal solution (using mild acidic solutions with controlled composition and concentration) and process parameters (temperature, time) to achieve selective removal. This allows the additive layer to be removed while the interdiffusion zone remains intact, preserving dimensional stability.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If aggressive acid treatment is used to remove the diffusion coating, then removal efficiency is high, but chemical attacks on the substrate increase

Engineering Contradiction:

Improvecoating removal rateVSAvoidchemical corrosion damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The removal process exploits the local quality difference between the additive layer and interdiffusion zone. The additive layer has high aluminum content and reacts readily with acid, while the interdiffusion zone has lower aluminum content and reacts slowly. This allows selective removal of the additive layer using mild acidic solutions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the chemical parameters of the removal solution (using mild acidic solutions with controlled composition and concentration) and process parameters (temperature, time) to achieve selective removal. This allows the additive layer to be removed while the interdiffusion zone remains intact, preserving dimensional stability.

Inventive Principle:

Principle #35Parameter changes

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 process enables refurbishment of diffusion aluminide coatings with minimal base material loss, reducing scrap rates and facilitating subsequent processing like welding and recoating, while maintaining component integrity and extending life cycles.

Implementation Method 1

a diffusion of aluminum into the substrate surface to a depth sufficient to form an interdiffusion zone

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

selective removal of the aluminum-infused additive layer with minimal removal of the interdiffusion zone and minimal removal of the substrate surface

Methodology Applied

Scientific EffectChemical etching:

Data Source

PatentEP3198050B1Method for selective aluminide diffusion coating removal

Publication Date: 2022.04.27 GENERAL ELECTRIC CO

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AI summary

A method for selective aluminide diffusion coating removal. The method includes diffusing aluminum into a substrate surface of a component to form a diffusion coating. The diffusion coating includes an aluminum-infused additive layer and an interdiffusion zone. The diffusion coating is solution heat treated at a temperature and for a time sufficient to dissolve at least a portion of the interdiffusion zone. Thereafter the aluminum-infused additive layer is selectively removed. An aluminide diffusion coated turbine component is also disclosed.