Blade Outer Air Seal Coating for CMAS-Resistant Abradability
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Solution Overview
Problem
Existing blade outer air seals in gas turbine engines face challenges with temperature and environmental resistance, particularly due to the reactive crystallization and infiltration of calcia-magnesia-alumino-silicate (CMAS) that degrade the abradable coatings, leading to mechanical stress and reduced lifespan.
Innovation Solution
A multilayer coating system is applied to the blade outer air seal, comprising a bond coat, an environmental barrier coating (EBC) with refractory metal oxides like HfSiO4 or ZrSiO4, and a CMAS-resistant abradable layer with porosity between 15-40%, designed to accommodate CMAS infiltration while maintaining abrasion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an abradable coating is applied to the blade outer air seal, then rub performance is improved, but temperature and environmental resistance deteriorates due to CMAS infiltration
Solution Approach 1:
The coating system is divided into multiple functional layers: an environmental barrier coating layer that resists CMAS infiltration, a bond coat layer for adhesion, and an abradable layer for rub performance. This segmentation allows each layer to specialize in one function, preventing CMAS from reaching the abradable layer while maintaining its rub characteristics.
Solution Approach 2:
The environmental barrier coating layer acts as an intermediary between the harsh external environment (CMAS, high temperature) and the abradable coating layer. It mediates the harmful effects by blocking CMAS infiltration and thermal exposure, protecting the underlying abradable layer from degradation.
2Reliability
If the abradable layer has high porosity to maintain abradability, then rub performance is improved, but environmental resistance deteriorates due to increased CMAS infiltration
Solution Approach 1:
The coating is segmented into an environmental barrier layer with low porosity (blocking CMAS) and an abradable layer with high porosity (maintaining abradability). The barrier layer's dense structure prevents CMAS from infiltrating into the porous abradable layer, allowing the abradable layer to maintain its required porosity for rub performance without environmental degradation.
Solution Approach 2:
The environmental barrier coating layer serves as a protective intermediary that blocks CMAS infiltration pathways. It shields the porous abradable layer from direct exposure to molten CMAS, allowing the abradable layer to maintain its porous structure for abradability without suffering from environmental degradation.
3Object-affected harmful factors
If a dense environmental barrier coating is applied, then CMAS resistance is improved, but abradability of the outer layer deteriorates
Solution Approach 1:
The coating system is segmented into two distinct layers with contrasting properties: a dense environmental barrier layer for CMAS resistance and a porous abradable layer for rub performance. The barrier layer's density prevents CMAS infiltration, while the abradable layer's porosity maintains its abradability, resolving the contradiction between these two requirements.
Solution Approach 2:
Different regions of the coating have different local qualities tailored to their specific functions. The environmental barrier layer has a dense, non-porous structure optimized for CMAS resistance, while the outer abradable layer has a porous structure optimized for abradability. Each layer's local quality is optimized for its specific role without compromising the other.
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 mitigates CMAS-induced degradation, enhancing the longevity and performance of the blade outer air seal by self-healing and reducing mechanical stress, while maintaining abradability.
Implementation Method 1
Pores of the abradable layer are configured to receive molten calcia-magnesia-alumino-silicate (CMAS)
Implementation Method 2
The environmental barrier coating is nonreactive with respect to calcia-magnesia-alumino-silicate (CMAS)
Implementation Method 3
an abradable layer disposed on the environmental barrier layer. The abradable layer has a porosity of between about 15 percent and about 40 percent
Data Source
Figure 1
Figure 2~3
AI summary
A blade outer air seal (105) includes a center web (105a) having a radially inner face (106) and a radially outer face, at least one mounting arm (105b) extending from the radially outer face, and a coating (200) disposed on the radially inner face (106). The coating (200) includes an environmental barrier coating layer and an abradable layer disposed on the environmental barrier layer. The abradable layer has a porosity of between about 15 percent and about 40 percent. A gas turbine engine and a method of protecting a blade outer air seal (105) are also disclosed.