Slurry-Based Thermal Barrier Coating Repair
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Solution Overview
Problem
Current methods for repairing thick ceramic thermal barrier coatings on gas turbine exhaust components are inadequate for in-situ, on-wing repairs due to safety concerns and lack of durable solutions, leading to frequent replacements and high costs.
Innovation Solution
A slurry-based repair technique involving a wet bond coat with glass or glass-ceramic particles and ceramic oxide particles, combined with metallic or ceramic fibers, which is applied and then heated to form a ceramic composite layer adhered to the metal substrate, using engine exhaust heat for pyrolysis, thereby providing mechanical adhesion and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current repair methods are used for thick ceramic thermal barrier coatings, then the repair process can be completed, but the repaired coating lacks durability and exhibits spalling and re-melting issues
Solution Approach 1:
The patent uses a composite slurry formulation containing glass particles (30-70 wt%), ceramic oxide particles (20-50 wt%), and binder (5-20 wt%). This composite material structure provides both durability through thermal stability and ease of manufacture through slurry applicability. The glass-ceramic composite forms a stable matrix that prevents spalling while maintaining repairability.
Solution Approach 2:
The patent controls the particle size distribution of glass particles (5-50 micrometers) and ceramic oxide particles (5-40 micrometers) to optimize both durability and application ease. The specific particle size parameters ensure proper slurry flow and deposition while creating a dense, durable repaired coating structure that resists spalling.
2Duration of action of stationary object
If traditional repair techniques are applied, then coating damage can be addressed, but frequent replacements are required due to lack of durable solutions
Solution Approach 1:
The repaired coating system is designed to be self-sufficient with the glass-ceramic composite providing inherent thermal stability and structural integrity. The coating bonds directly to the substrate through chemical adhesion mechanisms, creating a self-supporting structure that eliminates the need for frequent re-repairs or substrate replacements.
Solution Approach 2:
The glass particles undergo phase transition during heating, transforming from amorphous glass to glass-ceramic composite structure. This phase transition occurs at controlled temperatures and creates a stable, durable coating structure that resists thermal cycling damage, extending service life and reducing repair frequency.
3Ease of operation
If on-wing repair is attempted with current methods, then field repair capability is achieved, but safety concerns prevent reliable in-situ repairs
Solution Approach 1:
The patent replaces complex mechanical repair systems with a simplified slurry-based chemical deposition process. The slurry is applied directly to the damaged area and bonds through chemical adhesion mechanisms, eliminating the need for heavy equipment, complex assembly procedures, or hazardous operations that would compromise safety during on-wing repairs.
Solution Approach 2:
The slurry acts as an intermediary material that bridges the damaged coating area and the underlying substrate. This intermediary formulation provides a safe, controlled repair process that can be applied in the field without exposing workers to hazardous conditions, while still achieving durable repair results.
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 method enables cost-effective and time-efficient on-wing repair of damaged thermal barrier coatings, ensuring long-term structural integrity and thermal stability, as demonstrated by successful thermal cycling tests without spalling or re-melting issues.
Implementation Method 1
heating the bond coat melts at least a portion of the at least one of the glass particles or the glass-ceramic particles to form a fully amorphous glass phase or a mixture of amorphous and crystalline glass phases which bond with the metal substrate
Implementation Method 2
using engine exhaust heat for pyrolysis
Data Source
AI summary
In some examples, a method including applying a wet bond coat slurry to a damaged area of a coating system on a metal substrate, the bond coat slurry including a liquid binder, glass and/or glass-ceramic particles, and ceramic oxide particles; depositing fibers onto the wet bond coat slurry, wherein the fibers include metallic and/or ceramic fibers; applying a ceramic composite slurry on the bond coat while the bond coat is wet or at least partially dried to form a ceramic composite layer, the bond coat including a plurality of partially exposed fibers, wherein, following the application of the ceramic composite slurry, a first portion of fibers of the plurality of fibers are embedded in the bond coat and a second portion of fibers of the plurality of fibers extend into the layer of the ceramic composite slurry; and heating the bond coat and the ceramic composite layer to form a repaired portion of the coating system on the metal substrate, wherein heating the bond coat melts the glass particles and/or the glass-ceramic particles to form a fully amorphous glass phase or a mixture of amorphous and crystalline glass phases which bond with the metal substrate.