Chemical Vapor Deposition Bond Coating for Ceramic Matrix Composites
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Solution Overview
Problem
Existing protective coatings for ceramic matrix composite materials, such as SiC/SiC, in aggressive environments like gas turbines face challenges due to excessive thickness requirements for bond and barrier coatings, which can lead to mechanical stresses and coating failure.
Innovation Solution
A coating method involving chemical vapor deposition to form a bond coating with columnar grains of crystalline silicon, and a rare earth silicate barrier coating, applied with specific deposition parameters to achieve thin, effective coatings with reduced thickness and enhanced adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal spraying is used to apply protective coatings to ensure complete coverage, then coating coverage is improved, but coating thickness becomes excessive (at least 75 μm for bond coating and 100 μm for barrier coating)
Solution Approach 1:
The patent applies chemical vapor deposition instead of thermal spraying, fundamentally changing the deposition method parameters. This enables precise control of coating thickness at the micrometer scale while ensuring complete coverage of complex substrate geometries, resolving the contradiction between adequate coverage and excessive thickness
2Reliability
If bond coating thickness is increased to ensure complete coverage, then coating coverage is improved, but mechanical stresses increase leading to dome cracking and coating failure
Solution Approach 1:
By using chemical vapor deposition with controlled deposition parameters, the patent achieves complete coverage with bond coating thickness reduced to less than 20 μm. This precise thickness control prevents excessive mechanical stresses that would cause dome cracking, thereby maintaining coating integrity while ensuring complete coverage
Solution Approach 2:
The patent replaces the mechanical thermal spraying process with a chemical vapor deposition process. This substitution allows for more precise control of coating formation, enabling thin uniform coatings that cover complex geometries without generating harmful mechanical stresses
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 method allows for the achievement of bond and barrier coatings with maximum thicknesses of less than 20 μm and 40 μm respectively, providing improved resistance to aggressive environments and reducing the risk of mechanical stresses and coating failure.
Implementation Method 1
a step of forming a bond coating on a surface of a substrate by chemical vapor deposition of a precursor comprising silicon
Implementation Method 2
the step of forming the bond coating can be carried out with a deposition temperature greater than 1150° C., preferably equal to or greater than 1200° C.
Data Source
AI summary
A method including a step of forming a bond coating on a surface of a substrate, and a step of forming a barrier coating on the bond coating. The bond coating is formed by chemical vapor deposition, at a deposition temperature higher than 150° C., in particular 1200° C. or higher, of a precursor including silicon, and includes columnar grains of crystalline silicon.