Non-wetting Coating for Nodule-Free Ceramic Matrix Composites
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Solution Overview
Problem
The formation of silicon surface nodules during the melt infiltration process in the fabrication of silicon carbide-based ceramic matrix composites poses challenges related to dimensional tolerance, machining, and environmental barrier coating adhesion, as existing methods fail to effectively prevent or remove these nodules.
Innovation Solution
A method involving the application of a non-wetting coating with a contact angle of at least 45 degrees, composed of materials like boron nitride or silicon nitride, on the porous fibre preform surfaces, followed by a high-emissivity carbon coating, which inhibits molten silicon from penetrating the surface, thereby preventing nodule formation and allowing for easy removal of the coating post-infiltration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a porous fibre preform is infiltrated with molten silicon to form a ceramic matrix composite, then the composite achieves desired mechanical and thermal properties, but silicon surface nodules form on the outer surfaces during solidification
Solution Approach 1:
A non-wetting coating is applied to the outer surfaces of the porous fibre preform before melt infiltration. This preliminary coating prevents molten silicon from contacting and solidifying on the outer surfaces, thereby preventing nodule formation before the problem can occur during the infiltration and solidification process.
Solution Approach 2:
The non-wetting coating acts as an intermediary barrier between the molten silicon and the outer surfaces of the preform. This intermediate layer allows the molten silicon to infiltrate the porous structure while preventing it from solidifying on the surfaces, thus mediating between the infiltration process and surface quality requirements.
2Ease of manufacture
If conventional melt infiltration is used to fabricate SiC-based ceramic matrix composites, then the composite structure is formed, but removal of silicon surface nodules requires labor-intensive processes
Solution Approach 1:
The non-wetting coating is applied in advance to prevent nodule formation during the infiltration process. By taking preliminary preventive action, the need for subsequent labor-intensive nodule removal operations is eliminated, saving both labor and time in the manufacturing process.
Solution Approach 2:
The patent converts the potentially harmful effect of molten silicon contacting surfaces into a beneficial outcome by using the non-wetting coating to control where solidification occurs. The coating transforms what would be a problematic surface contact into a controlled process that prevents nodules while maintaining infiltration effectiveness.
3Manufacturing precision
If a non-wetting coating is applied to prevent molten silicon penetration, then surface quality is improved, but the coating must be removed after infiltration
Solution Approach 1:
The non-wetting coating is applied as a temporary, disposable layer that serves its protective function during infiltration and is then removed. This short-lived coating is inexpensive and easily applied/removal compared to the benefits of producing nodule-free surfaces, making the additional process steps worthwhile.
Solution Approach 2:
The patent changes the surface properties of the preform by applying a coating with different wetting characteristics. This parameter change (surface energy/wettability) allows control over molten silicon behavior during infiltration, and the coating can be removed after serving its purpose, demonstrating a temporary parameter modification to solve the surface quality issue.
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 approach results in ceramic matrix composites that are substantially free of silicon surface nodules, eliminating the need for labor-intensive nodule removal and enhancing the composite's performance by maintaining a smooth surface, suitable for applications in gas turbine engines.
Implementation Method 1
The non-wetting coating comprises a non-wetting material with which molten silicon has a contact angle of at least about 45 degrees, the non-wetting material being selected from the group consisting of boron nitride, aluminium nitride and silicon nitride
Implementation Method 2
A high-emissivity coating comprising a non-reflective material is applied onto the non-wetting coating, the non-reflective material comprising carbon
Implementation Method 3
the molten material is infiltrated into the porous fibre preform through the uncoated portion
Data Source
Figure 1~2B
Figure 3~4
AI summary
A method of melt infiltration for producing a ceramic matrix composite (108) comprises applying a non-wetting coating (102) onto one or more outer surfaces of a porous fibre preform (104). The non-wetting coating comprises a non-wetting material with which molten silicon has a contact angle (θc) of at least about 45 degrees. After applying the non-wetting coating, an uncoated portion (104b) of the porous fibre preform is immersed into a molten material (106) comprising silicon, and the molten material is infiltrated into the porous fibre preform through the uncoated portion. The non-wetting coating serves as a barrier to inhibit or prevent the molten material from penetrating the one or more outer surfaces. After infiltration of the molten material into the porous fibre preform, the molten material is cooled to form a ceramic matrix composite (108), and the non-wetting coating is removed.