CMAS-Resistant Coatings for CMC Blade Outer Air Seals
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Solution Overview
Problem
Ceramic matrix composite (CMC) components in gas turbine engines face challenges with wear resistance and durability, particularly in environments exposed to calcium magnesium aluminosilicate (CMAS) attack, where existing coatings do not adequately prevent spalling and delamination.
Innovation Solution
A layer comprising hafnium silicate, zirconium silicate, ytterbium disilicate, and barium magnesium aluminosilicate (BMAS) is applied to the internal surfaces of blade outer air seal segments, providing a wear-resistant coating that can withstand high temperatures and CMAS exposure, with a thickness of 0.05 mm to 0.50 mm, applied via ultrasonic spraying and subsequent heating in an oxidizing environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing coatings are applied to CMC components, then wear resistance should be improved, but the coatings fail to prevent spalling and delamination under CMAS attack
Solution Approach 1:
The patent applies a composite coating system consisting of multiple layers: a bond coat layer containing alumina and silica, and a topcoat layer containing hafnium silicate, zirconium silicate, and BMAS. This multi-layer composite structure provides both wear resistance and protection against CMAS attack, with each layer serving specific functions to address the contradictory requirements.
Solution Approach 2:
The patent modifies the chemical composition parameters of the coating materials by incorporating specific ratios of hafnium oxide (5-20 wt%), zirconium oxide (5-20 wt%), and BMAS (1-10 wt%) to achieve optimal resistance to both wear and CMAS attack. The composition parameters are carefully controlled to balance the competing requirements.
2Duration of action of stationary object
If a thick protective layer is applied to prevent spalling and delamination, then durability should be improved, but the coating complexity and manufacturing difficulty increase
Solution Approach 1:
The protective coating is segmented into distinct functional layers: a bond coat layer (50-200 micrometers thick) and a topcoat layer (50-150 micrometers thick). This segmentation allows each layer to be optimized for its specific function while maintaining overall durability, and enables independent control of each layer's composition and thickness during manufacturing.
Solution Approach 2:
The bond coat layer is applied first to the CMC substrate to establish a stable foundation that prevents delamination. This preliminary action creates a robust interface between the substrate and the subsequent topcoat layer, ensuring long-term durability before the final protective layer is applied.
3Reliability
If multiple coating layers are applied to enhance wear resistance and CMAS protection, then reliability should be improved, but the manufacturing process becomes more complex
Solution Approach 1:
The bond coat layer acts as an intermediary between the CMC substrate and the topcoat layer, facilitating adhesion and providing a transition zone. This intermediary layer simplifies the manufacturing process by ensuring reliable bonding between the substrate and topcoat, reducing the risk of delamination without requiring complex manufacturing techniques.
Solution Approach 2:
The patent employs thermal spray deposition techniques to apply the coating layers, replacing more complex mechanical coating methods. This substitution enables precise control of layer thickness and composition while simplifying the manufacturing process, and allows for automated application of the multi-layer structure.
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 BMAS-containing layer enhances the wear resistance and durability of CMC components, reducing the likelihood of spalling and delamination when exposed to CMAS, thereby improving the longevity and performance of gas turbine engine components.
Implementation Method 1
A slurry comprising a binder and particulate matter including at least one of hafnium oxide (HfO2), zirconium oxide (ZrO2) and ytterbium oxide (Yb2O3); silicon carbide (SiC); silicon (Si) and barium magnesium aluminosilicate (BMAS) or other alkaline earth aluminosilicate is applied to a ceramic matrix composite (CMC) component
Implementation Method 2
The slurry is heated to a peak temperature of 1450° C. to a peak temperature of at least 1450° C. in an oxidizing environment
Implementation Method 3
The slurry is applied via ultrasonic spraying
Data Source
AI summary
A blade outer air seal has at least one internal surface and a layer atop the at least one internal surface. The layer has: a matrix comprising at least one of hafnium silicate (HfSiO4) and zirconium silicate (ZrSiO4), ytterbium disilicate (Yb2Si2O7); and barium magnesium alumino silicate (BMAS) or other alkaline earth aluminosilicate.