Tape-Deposited Sacrificial Coating for CMC Blade Tip Wear
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Solution Overview
Problem
CMC blade tips in gas turbine engines face wear issues due to rub events with metal shrouds, leading to EBC coating wear and reduced engine efficiency, as existing coatings are susceptible to oxidation and high-temperature steam penetration.
Innovation Solution
A thick, tape-deposited sacrificial coating system comprising a bond coat, multiple rare earth silicate layers, and an outer layer is applied to the CMC blade tip, providing mechanical resistance and hermeticity, with the sacrificial coating designed to absorb rub impacts and protect underlying layers from high-temperature steam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin EBC coating is applied to CMC blade tip, then the coating provides basic oxidation protection, but the coating wears away during rub events with metal shrouds, exposing the CMC to steam penetration and clearance opening
Solution Approach 1:
The coating system is divided into multiple functional layers: a sacrificial outer layer (4-40 mils thick) that absorbs wear during rub events, and underlying protective layers (bond coat and EBC layers) that provide oxidation and steam protection. This segmentation allows each layer to specialize in one function, resolving the contradiction between wear resistance and protection reliability.
Solution Approach 2:
The sacrificial outer layer is designed to be consumed during rub events, acting as a cushion that absorbs the mechanical wear before it reaches the critical EBC layers. This beforehand cushioning ensures that the underlying protective layers remain intact to maintain their protective function even after prolonged operation with periodic rub events.
2Productivity
If the blade tip clearance is reduced to improve efficiency, then the space between blade tip and shroud is minimized, but the EBC coating becomes more susceptible to wear from increased contact with the shroud
Solution Approach 1:
The thick sacrificial outer layer (4-40 mils) is applied beforehand to the blade tip, creating a wear buffer that absorbs contact with the shroud during operation. This allows the blade to operate with reduced clearance for improved efficiency while the sacrificial layer protects the critical EBC layers from wear, resolving the contradiction between productivity and wear susceptibility.
3Strength
If a thick sacrificial coating is applied to the blade tip to protect against wear, then the coating absorbs rub impacts effectively, but the coating thickness increases manufacturing complexity and deposition time
Solution Approach 1:
The coating system segments the thick protective function into a dedicated sacrificial outer layer (4-40 mils) that can be applied using tape deposition methods. This segmentation allows the thick wear-resistant layer to be applied separately from the underlying EBC layers, simplifying the manufacturing process while maintaining the required rub impact absorption capability.
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 effectively reduces wear and oxidation, maintaining engine efficiency by sacrificing the sacrificial layer during rub events and providing hermetic protection against high-temperature steam, thereby enhancing the durability and performance of CMC blade tips.
Implementation Method 1
the EBC at the blade tip is susceptible to rub against metal shroud components. If the EBC coating wears away, the CMC blade is then open to recessive attack
Implementation Method 2
a first rare earth silicate coating on the bond coat; a sacrificial coating of a reinforced rare earth silicate matrix on the at least one rare earth silicate layer
Data Source
Figure 1
Figure 2~3
AI summary
Coating systems (20) are provided for use on a CMC substrate (24), that can include: a bond coat (26) on a surface (25) of the CMC substrate (24); a first rare earth silicate coating (28a) on the bond coat; a sacrificial coating (30) of a reinforced rare earth silicate matrix on the at least one rare earth silicate layer; a second rare earth silicate coating (28b) on the sacrificial coating; and an outer layer (32) on the second rare earth silicate coating. The first rare earth silicate coating comprises at least one rare earth silicate layer, and the second rare earth silicate coating comprises at least one rare earth silicate layer. The sacrificial coating has a thickness of about 4 mils to about 40 mils. Methods are also provided for tape deposition of a sacrificial coating on a CMC substrate.