Turbine Component Ceramic Coating Resists Corrosion
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Solution Overview
Problem
Turbine disks, shafts, and seal elements in gas turbine engines face corrosion issues due to high operating temperatures, with existing corrosion-resistant coatings either affecting mechanical properties, causing spalling, or being complex and expensive to apply.
Innovation Solution
A ceramic corrosion-resistant coating comprising zirconia or hafnia is applied using methods like sol-gel processing, physical vapor deposition, or thermal spraying, which does not diffuse into the substrate, maintains fatigue properties, and provides better adherence to prevent spalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum or chromium diffusion coatings are applied to turbine disks/shafts, then corrosion resistance is improved, but fatigue life is adversely affected due to diffusion into the substrate
Solution Approach 1:
The patent introduces a bond coat as an intermediary layer between the metal substrate and the ceramic top coat. This bond coat prevents direct diffusion between the aluminum/chromium coating and the metal substrate, thereby protecting the substrate's fatigue properties while still providing corrosion resistance through the ceramic layer.
Solution Approach 2:
The coating system is divided into separate functional layers: a bond coat layer that protects the substrate and a top coat layer that provides corrosion resistance. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between corrosion protection and fatigue life preservation.
2Reliability
If ceramic coatings are applied to turbine components, then corrosion resistance at high temperatures is improved, but the coating becomes prone to spalling due to CTE mismatch with the metal substrate
Solution Approach 1:
The patent modifies the coating system parameters by introducing a bond coat layer with intermediate thermal expansion properties between the ceramic top coat and the metal substrate. This gradient in CTE values reduces the thermal stress and CTE mismatch, preventing coating spalling while maintaining corrosion resistance.
3Manufacturing precision
If chemical vapor deposition is used to deposit corrosion resistant coating, then coating quality is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces complex chemical vapor deposition processes with simpler application methods such as brush application, spray application, or dip coating for the sol-gel precursor. This substitution maintains coating quality while significantly reducing manufacturing complexity and cost.
4Reliability
If thicker ceramic coatings are applied to increase corrosion protection, then corrosion resistance is improved, but the coating is more prone to spalling and affects mechanical properties
Solution Approach 1:
The patent employs a thin ceramic top coat layer (typically 0.5-5 mils) rather than thick coatings. The sol-gel process enables formation of uniform thin films that provide adequate corrosion protection without creating the stress and brittleness associated with thicker coatings, thereby preventing spalling and preserving mechanical properties.
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 ceramic coating effectively resists corrosion at elevated temperatures without affecting the mechanical properties of turbine components, reducing the risk of spalling and extending their lifespan by forming a stable, thin layer that is inexpensive and uncomplicated to apply.
Implementation Method 1
heating the gel-forming solution to a first preselected temperature for a first preselected time to form a gel; depositing the gel on the metal substrate; and firing the deposited gel at a second preselected temperature above the first preselected temperature to form a ceramic corrosion resistant coating
Implementation Method 2
depositing a ceramic composition comprising a ceramic metal oxide on the metal substrate by physical vapor deposition to form a ceramic corrosion resistant coating
Implementation Method 3
thermal spraying a ceramic composition comprising a ceramic metal oxide on the metal substrate to form the ceramic corrosion resistant coating
Data Source
AI summary
An article comprising a turbine component other than an airfoil having a metal substrate and a ceramic corrosion resistant coating overlaying the metal substrate. This coating has a thickness up to about one micrometer and consists of a ceramic composition that comprises a ceramic metal oxide selected from the group consisting of zirconia, hafnia and mixtures thereof. This coating can be formed by alternative methods to have different microstructures, including a dense matrix or a strain-tolerant columnar grain structure.