Environmental Barrier Coating Sintered Layer Surface Roughness
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Solution Overview
Problem
Current environmental barrier coatings (EBCs) applied using plasma spray processes have surface roughness issues, which are undesirable for aerodynamic design in high-temperature gas turbine engines, and there is a need for improved methods to protect ceramic components from high-temperature steam environments.
Innovation Solution
A plasma sprayed environmental barrier coating with a sintered layer formed from a water-based slurry containing sintering aids, such as iron, aluminum, and rare earth metals, which reduces surface roughness and provides a hermetic seal by densifying the coating at lower temperatures, preventing corrosion and dimensional changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plasma spray process is used to apply environmental barrier coating, then the coating provides hermetic seal and protection, but the surface roughness becomes greater than 200 micro inch Ra which is undesirable for aerodynamic design
Solution Approach 1:
The coating system is divided into two distinct layers: a plasma-sprayed environmental barrier coating layer that provides hermetic seal and corrosion protection, and a separate sintered topcoat layer that provides smooth aerodynamic surface. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The topcoat is formulated as a composite slurry containing ceramic particles (such as alumina, silica, or zirconia), organic binders, and plasticizers. This composite structure enables the topcoat to achieve both adhesion to the plasma-sprayed layer and smooth surface finish after sintering.
2Manufacturing precision
If slurry deposition process is used to apply topcoat, then surface roughness is reduced and uniform thickness is achieved, but additional processing steps are required
Solution Approach 1:
The topcoat slurry application and sintering processes are combined into a single integrated step that occurs after plasma spraying. The slurry is applied to the plasma-sprayed coating and then sintered in one continuous operation, reducing the need for separate intermediate processing steps.
Solution Approach 2:
The organic binders and plasticizers in the topcoat slurry automatically provide binding and surface smoothing functions during the sintering process, eliminating the need for separate binder application or surface finishing operations. The slurry self-levels and self-binds during drying and sintering.
3Ease of manufacture
If sintering aid is added to slurry, then sintering temperature is reduced and manufacturing cost decreases, but composition control becomes more complex
Solution Approach 1:
Sintering aids such as boron oxide, silicon oxide, or rare earth oxides are added to the topcoat slurry to lower the sintering temperature from typical ceramic sintering temperatures (above 1600°C) to more economical temperatures (1200-1500°C). This parameter change in sintering temperature directly reduces energy consumption and manufacturing cost.
Solution Approach 2:
The sintering aid is specifically incorporated into the topcoat slurry formulation rather than the plasma-sprayed EBC layer, creating local compositional differentiation. This allows the topcoat to sinter at lower temperatures while the underlying EBC layer maintains its protective function, optimizing both cost and performance.
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 solution achieves a significant reduction in surface roughness of EBCs, enhancing their durability and resistance to high-temperature steam, while maintaining mechanical properties and reducing manufacturing costs through the use of a slurry deposition process, allowing for uniform thickness and smooth surface finishes.
Implementation Method 1
the inclusion of a sintering aid can lower the sintering temperature of the coating material
Implementation Method 2
through chemical reactions
Implementation Method 3
standard, industrial coating processes such as plasma spray
Data Source
AI summary
Components having an environmental barrier coating and a sintered layer overlying the environmental barrier coating, the sintered layer defining an outer surface having a lower surface roughness than the environmental barrier coating. The sintered layer is formed from a slurry applied to and then sintered on the environmental barrier coating. The sintered layer comprises a primary material, at least one sintering aid dissolved in the primary material, and optionally a secondary material. The sintering aid contains at least one doping composition. The primary material is a rare earth disilicate or a rare earth monosilicate and is doped with the doping composition so as to be either a doped rare earth disilicate or a doped rare earth monosilicate. The optional secondary material is a reaction product of the primary material and any of the sintering aid not dissolved in the primary material.