Beveled Substrate Channels for Thermal Barrier Coating Edges
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Solution Overview
Problem
Delamination or spalling of thermal barrier coatings from their underlying substrates in gas turbine engines due to differential thermal expansion and contamination, such as calcium magnesium alumino-silicate (CMAS) attack, which reduces the coating's ability to accommodate thermal deformations.
Innovation Solution
The implementation of a substrate with a bevel surface featuring a pattern of first and second channels of different sizes and registry, along with recesses, to create initiation sites for faults in the ceramic coating, allowing for thermal expansion accommodation and stress relief, combined with a ceramic coating of stabilized zirconia applied using machining and grinding techniques to ensure a smooth contour.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a ceramic coating is applied to a substrate in gas turbine engines, then thermal barrier protection is provided, but differential thermal expansion and CMAS attack cause delamination and spalling
Solution Approach 1:
The coating system is segmented into multiple functional layers: a ceramic topcoat layer for thermal barrier protection, a patterned interlayer with recesses and channels that creates fault lines, and a metallic bondcoat layer. The patterned interlayer segments the ceramic coating into discrete regions, allowing independent thermal expansion and contraction without compromising overall adhesion.
Solution Approach 2:
The interlayer is provided with a non-uniform pattern of recesses and channels at specific locations where thermal stress and CMAS attack are most severe. This creates localized fault lines precisely where needed to accommodate differential thermal expansion, while maintaining coating integrity in less critical areas.
2Temperature
If the ceramic coating is made continuous and uniform, then thermal barrier performance is optimized, but stress concentration occurs at edges and interfaces leading to spallation
Solution Approach 1:
The continuous ceramic coating is transformed into a segmented structure through the patterned interlayer with recesses and channels. This segmentation creates fault lines that prevent stress propagation across the entire coating, thereby reducing stress concentration at edges and interfaces while maintaining adequate thermal barrier performance through the ceramic topcoat layer.
Solution Approach 2:
The patterned interlayer with recesses and channels is applied beforehand to create predetermined fault lines that will accommodate thermal stress before it builds up to critical levels. These pre-established stress relief pathways prevent sudden catastrophic failure by allowing controlled deformation at designated locations.
3Stability of the object's composition
If CMAS contamination occurs on the coating surface, then the coating's ability to accommodate thermal expansion is reduced, but the coating structure remains intact
Solution Approach 1:
The recesses and channels are strategically positioned in areas most susceptible to CMAS accumulation and thermal stress. By concentrating stress-relief features at these critical locations, the design maintains coating integrity in protected areas while providing localized adaptability for thermal deformation where contamination is most likely to occur.
Solution Approach 2:
The patterned interlayer acts as an intermediary between the ceramic topcoat and the metallic bondcoat, providing a transition zone that accommodates differential thermal expansion. The recesses and channels in this interlayer create fault lines that allow the ceramic coating to deform thermally even when contaminated with CMAS, preventing direct transmission of stress to the substrate.
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 configuration enhances the thermal spallation resistance and stress tolerance of the ceramic coatings, reducing the likelihood of delamination and spalling at high-temperature edges, thereby improving the durability and performance of gas turbine engine components.
Implementation Method 1
A principal driver of delamination is differential thermal expansion/contraction of the coating and the underlying substrate
Implementation Method 2
With typical plasma spray coatings, the initiation may be the creation of boundaries/gaps between regions of the as-applied coating
Data Source
AI summary
In a method for manufacturing an article, the article has a body having: a first face; and a first bevel surface extending from the first face. A plurality of first channels along the first bevel surface extending from the first face. A ceramic coating is along the inner diameter surface and the first bevel surface. Each of the first channels are machined in the body by plunging a rotating bit into the first surface and drawing the rotating bit down the bevel surface. The coating is thereafter applied.