Cobalt-Based Coating with Sacrificial Particles for Corrosion Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Compressor blades in gas turbine engines, made of martensitic stainless steel and coated with cobalt-based alloys, are susceptible to galvanic corrosion in corrosive environments, especially when exposed to acidic conditions or exhaust gas recirculation systems, leading to crevice corrosion and pitting.
Innovation Solution
A cobalt-based wear coating with sacrificial metal-based particles such as NiO, cerium oxide, Cr2O3, and Al2O3 is applied over the martensitic stainless steel blades, acting as an anode to prevent galvanic corrosion by becoming sacrificial in a corrosive environment, thereby protecting the base material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a cobalt-based wear coating is applied over martensitic stainless steel compressor blades, then erosion and abrasion resistance is improved, but galvanic corrosion susceptibility increases in corrosive environments
Solution Approach 1:
The patent applies a composite coating system consisting of a cobalt-based wear-resistant alloy coating combined with a corrosion-resistant overlay coating. This multi-layer composite structure provides both erosion/abrasion protection from the cobalt-based layer and galvanic corrosion resistance from the corrosion-resistant overlay, resolving the contradiction between wear resistance and corrosion resistance.
Solution Approach 2:
The patent applies different coating properties to different regions or layers: the underlying cobalt-based coating provides wear resistance where needed, while the outer corrosion-resistant overlay provides galvanic corrosion protection. This localized application of different material properties allows simultaneous achievement of both wear and corrosion resistance.
2Object-affected harmful factors
If exhaust gas recirculation is implemented to reduce CO2 emissions, then environmental performance is improved, but corrosion susceptibility of compressor blades increases due to higher concentration of corrosive chemicals
Solution Approach 1:
The patent converts the harmful effect of exhaust gas recirculation (increased corrosion risk) into a benefit by designing a corrosion-resistant coating system that not only protects against the original corrosive environment but also specifically withstands the enhanced corrosion conditions created by SEGR. The corrosion-resistant overlay transforms the problematic SEGR environment into an acceptable operating condition.
3Ease of operation
If on-line wash systems or fogging systems are used to clean blades or enhance compressor efficiency, then operational cleanliness or efficiency is improved, but corrosive environment formation increases when contaminants combine with moisture
Solution Approach 1:
The patent applies a corrosion-resistant coating overlay before the blades are exposed to the corrosive environment created by on-line wash or fogging systems. This pre-applied protective layer acts as a cushion against the corrosive effects of moisture combined with contaminants, allowing the cleaning or efficiency-enhancement operations to proceed without causing damage to the underlying metal.
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 effectively prevents galvanic corrosion, including crevice corrosion and pitting, allowing the compressor blades to operate in hostile environments without premature degradation, reducing maintenance needs and extending the lifespan of the gas turbine engine.
Implementation Method 1
compressor blades, such as compressor blades formed from a martensitic stainless steel such as GTD-450 and coated with a cobalt-based coating such as STELLITE, are subject to attack simply as a result of the environment in which they are used. The blades may be subject to galvanic corrosion when used in an environment which may be acidic.
Implementation Method 2
particles of a sacrificial metal-based material distributed through the cobalt-based coating. The sacrificial material acts as an anode to prevent galvanic corrosion of the base material in a corrosive environment.
Data Source
Figure 1
Figure 2
AI summary
A compressor blade (100) for use in a compressor section of a gas turbine engine, comprising: a martensitic stainless steel compressor blade and an abrasive coating having an anodic component. The compressor blade (100) has a blade portion (110), a dovetail portion (120) and a platform portion (130) intermediate the blade portion (110) and the dovetail portion (120), the blade portion (110) terminating in a tip (140) opposite the dovetail portion. A cobalt-based coating overlies at least the blade portion (110) of the compressor blade (100). The cobalt-based coating comprises a cobalt based material that includes precipitates of tungsten carbide that provide erosion resistance and particles of a sacrificial metal-based material distributed through the cobalt-based coating that provide galvanic corrosion resistance to the system.