Compressor Case Coating Resolving Galvanic Corrosion

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Solution Overview

Problem

Conventional abradable coatings on compressor cases in gas turbine engines are prone to delamination due to galvanic corrosion, especially in maritime environments where salt water exposure creates electrolytic potential differences, leading to reduced engine efficiency and lifespan.

Innovation Solution

A coating system comprising a dense layer with a higher density than the abradable top layer, which acts as a seal to prevent the ingress of electrolytic solutions, reducing galvanic corrosion and increasing the tensile strength of the coating system. The dense layer is formed using plasma spray techniques with argon or nitrogen gas, and the top coat is applied using similar methods with different plasma currents to achieve optimal density and porosity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a porous abradable layer is used on the compressor case, then the blade response is dampened and blade rub is reduced, but salt water can penetrate through the porous layer and cause galvanic corrosion at the interface

Engineering Contradiction:

Improveblade response dampingVSAvoidgalvanic corrosion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The coating system is divided into multiple functional layers: a porous abradable top layer for blade response damping, and a dense barrier layer beneath it to prevent salt water penetration. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between porosity-induced corrosion and porosity-induced damping.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The dense barrier layer acts as an intermediary between the porous abradable layer and the compressor case substrate. It mediates by blocking salt water from reaching the interface while still allowing the porous layer above to perform its damping function, thus preventing galvanic corrosion without eliminating the beneficial porosity effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If conventional top coats are used that allow egress of salt water, then the porous structure maintains its damping properties, but galvanic corrosion occurs at the interface

Engineering Contradiction:

Improveporous structure stabilityVSAvoidcorrosion resistance

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

Different regions of the coating system have different densities and permeability properties. The top layer maintains high porosity for damping, while the underlying barrier layer has low porosity for corrosion protection. This local differentiation of material properties allows simultaneous achievement of damping stability and corrosion resistance.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The coating system uses composite material structure combining porous abradable material (e.g., aluminum-silicon alloy) with a dense barrier layer. This composite approach integrates the beneficial properties of both porous and dense materials, achieving both damping functionality and corrosion resistance that neither material could provide alone.

Inventive Principle:

Principle #40Composite materials

3Reliability

If the abradable layer is made more porous to enhance damping, then blade response is better dampened, but more salt water can penetrate and accumulate at the interface

Engineering Contradiction:

Improveblade response dampingVSAvoidsalt water accumulation

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The invention converts the potentially harmful effect of salt water penetration through the porous layer into a beneficial outcome by using the porous structure to channel and manage fluid flow while the dense barrier layer captures and contains any penetrated moisture, preventing it from reaching the interface and causing corrosion.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 significantly reduces galvanic corrosion, increases the ultimate tensile strength, and extends the lifespan of the compressor case by preventing electrolyte accumulation and enhancing the bond between layers, making it suitable for maritime gas turbine engines.

Implementation Method 1

The dense layer is formed using plasma spray techniques with argon or nitrogen gas

Methodology Applied

Scientific EffectPlasma spray: Plasma Spray

Implementation Method 2

salt water may enter the porous, abradable layer and collect at the interface of the porous layer and the compressor case or other coating material. The external fluid, such as salt water, can thereby create an environment for galvanic corrosion due to galvanic potential differences

Methodology Applied

Scientific EffectGalvanic corrosion:

Data Source

PatentUS10823199B2Galvanic corrosion resistant coating composition and methods for forming the same

Publication Date: 2020.11.03 GENERAL ELECTRIC CO

AI summary

Coating systems for components of a gas turbine engine, such as a compressor case, are provided. The coating system can include a dense layer disposed along the inner surface of the compressor case as well as an abradable, top coat disposed along the dense layer. The combination of dense layer and abradable top coat can reduce the occurrence of galvanic corrosion of the coating system and thereby increase the lifetime of the coating system and preserve blade clearances within the compressor. Methods are also provided for applying the coating system onto a compressor case.