Rare-Earth Silicate Bond Coat for Turbine Heat Resistance
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Solution Overview
Problem
Existing coating structures for high-temperature applications, such as those in aviation and industrial gas turbines, face challenges in enhancing heat resistance and airtightness, particularly with bond coat films made from MCrAlY alloys which fail to provide adequate protection at elevated temperatures.
Innovation Solution
A coating structure featuring a bond coat layer formed from rare-earth silicate with compressive residual stress, layered directly on a ceramic matrix composite base, and a top coat layer, which increases airtightness and oxidation resistance by controlling oxygen permeability and crystal structure, and incorporating dispersed materials like silicon or titanium for enhanced toughness and creep resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bond coat film is formed from MCrAlY alloy, then the coating structure provides basic protection, but the heat resistance cannot be enhanced for high-temperature environments
Solution Approach 1:
The invention changes the material composition parameter of the bond coat layer from conventional MCrAlY alloy to rare-earth silicate containing specific elements (Hf, Ta, W, Mo, Nb, or their combinations). This parameter change enables the coating to maintain structural stability and protective function at temperatures of 1200°C and above, resolving the heat resistance limitation of traditional alloys
Solution Approach 2:
The invention creates a composite bond coat layer by combining rare-earth silicate with refractory metal elements (Hf, Ta, W, Mo, Nb). This composite structure provides both the high-temperature stability of rare-earth silicate and the enhanced mechanical properties from refractory metals, achieving superior heat resistance and reliability simultaneously
2Reliability
If the bond coat layer is made compact with compressive residual stress, then airtightness and oxidation resistance increase, but the structure becomes more complex to manufacture
Solution Approach 1:
The invention utilizes the self-organizing capability of rare-earth silicate materials during the thermal spray process. The material naturally forms a compact structure with compressive residual stress through controlled cooling and phase transformation, eliminating the need for additional post-treatment processes to achieve the desired stress state and compactness
Solution Approach 2:
The invention controls the crystallization parameters of rare-earth silicate during coating formation, specifically managing the phase transformation from amorphous to crystalline state. This parameter control enables the development of compressive residual stress and compact microstructure inherent to the material system, simplifying the manufacturing process
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 structure significantly enhances heat resistance and airtightness, allowing protection of turbine parts in high-temperature environments beyond 1200°C, with improved crack resistance and extended oxidation resistance due to the self-healing properties of dispersed materials.
Implementation Method 1
In the bond coat layer, the residual stress is compressive residual stress
Implementation Method 2
the crystal ratio of the bond coat layer is preferably from 90% to 100%. In this case, occurrence of cracking and separation due to a change in volume with crystallization in a usage environment of the bond coat layer can be suppressed, and the airtightness can be increased
Implementation Method 3
Due to silicon oxide or titanium oxide produced by oxidation of dispersed particles, a self-healing function of closing a crack is expressed
Data Source
AI summary
Provided are a coating structure, a turbine part having the same, and a method for manufacturing the coating structure. The coating structure is provided on a surface of a base portion including a ceramic matrix composite. The coating structure is layered on the surface of the base portion, and includes a bond coat layer formed of a rare-earth silicate and a top coat layer layered on the bond coat layer. The residual stress present in the bond coat layer is compressive residual stress. The oxygen permeability coefficient of the bond coat layer is no greater than 10−9 kg·m−1·s−1 at a temperature of not lower than 1200° C. and a higher oxygen partial pressure of not less than 0.02 MPa. The bond coat layer may contain carbonitride particles or carbonitride whiskers.