CMC Coating Wear Resistance via Silicate Binder
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Solution Overview
Problem
Oxide-based ceramic matrix composite substrates in gas turbine engines experience high and variable wear rates due to their porous nature and lack of adhesion with traditional coatings, leading to undesirable recession and degradation in high-temperature, oxidative environments.
Innovation Solution
A solid coating formed from a slurry comprising a liquid binder such as sodium silicate, applied directly to the substrate without a bond coat, providing a thickness range of 5 μm to 500 μm and enhancing wear resistance through a single annealing cycle, which adheres to the substrate and maintains stability across the required temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional coating is applied to oxide-based CMC substrate, then the coating provides some protective function, but the coating fails to adhere properly due to chemical inertness and lack of surface features
Solution Approach 1:
The substrate surface is treated beforehand with sandblasting or chemical etching to create roughness and increase surface area, providing mechanical interlocking features before the coating is applied. This preliminary surface preparation enables the coating to adhere properly without requiring complex bonding processes.
Solution Approach 2:
A bond coat layer is introduced as an intermediary between the CMC substrate and the protective coating. This bond coat chemically bonds to both the substrate and the outer coating, serving as a mediator that overcomes the chemical inertness of the CMC substrate and enables reliable adhesion of the protective coating.
2Strength
If the CMC substrate has high porosity (30-50%), then the material has good toughness and damage tolerance, but liquid precursor coating penetration becomes extremely difficult
Solution Approach 1:
The coating process is specifically designed to utilize the porous structure of the CMC substrate. A slurry-based precursor is applied that can penetrate through the porous network, followed by controlled drying and sintering that allows the coating material to infill the pores and form a mechanically interlocked structure with the substrate.
Solution Approach 2:
The viscosity and composition of the coating precursor are carefully controlled to match the pore size distribution of the substrate. The slurry is formulated with specific rheological properties that enable it to penetrate the porous structure at room temperature or with minimal heating, followed by thermal processing that consolidates the coating within the pore structure.
3Reliability
If bond coats and surface treatments are used to improve coating adhesion, then the adhesion level increases, but the process complexity and potential failure points increase
Solution Approach 1:
The bond coat application and protective coating application are combined into a single integrated process step. The slurry precursor contains both the bonding agents and the protective coating materials in one formulation, eliminating the need for separate bond coat deposition and reducing the number of process steps and potential failure points.
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 significantly reduces wear rates by up to two orders of magnitude, providing a stable and adherent surface that withstands mechanical contact and harsh environmental conditions, thus extending the lifespan of engine components.
Implementation Method 1
a solid coating formed from a precursor comprising a liquid binder selected from the group consisting of a sodium silicate
Implementation Method 2
consolidated by a thermal processing cycle
Implementation Method 3
The slurry is consolidated to form a wear resistant solid coating on the article
Data Source
AI summary
Coated articles adapted to be subjected to direct and sustained mechanical contact are provided. The coated articles include a ceramic matrix composite (CMC) substrate. A solid coating is disposed directly on and adheres to the substrate during such direct and sustained mechanical contact. The solid coating is formed from a precursor comprising a liquid binder, which may be sodium silicate, a basic colloidal alumina solution, aluminum hydroxide, aluminum oxychloride, aluminum hydroxylchloride, aluminum phosphate, and phosphoric acid. The coating may also include a filler material such as solid powder, chopped fibers, and combinations thereof.Methods for improving the wear resistance of an article made from the CMC substrates are also provided. A CMC substrate is provided and covered with a slurry. The slurry includes the liquid binder and optionally, the filler material. The slurry is consolidated, for example, by annealing to form a wear-resistant solid coating on the article.