Vanadium Resistant Coating System for Gas Turbines
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Solution Overview
Problem
Thermal barrier coatings used in gas turbine engines are susceptible to attack by vanadium oxide by-products from heavy fuel oil combustion, leading to deterioration and reduced lifespan of superalloy components.
Innovation Solution
A coating system comprising a bond coat and a ceramic coating with zirconium oxide stabilized by rare earth elements, along with a sacrificial top coat, provides enhanced resistance to vanadium oxide attack, extending the lifespan of superalloy components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If YSZ thermal barrier coating is used to protect superalloy components, then thermal protection performance is improved, but resistance to vanadium oxide attack deteriorates
Solution Approach 1:
The patent introduces a bond coat layer as an intermediary between the YSZ thermal barrier coating and the superalloy substrate. This bond coat acts as a mediator that provides resistance to vanadium oxide attack while allowing the YSZ layer to maintain its thermal protection function. The bond coat serves as a sacrificial barrier that prevents direct contact between vanadium oxide and the substrate.
Solution Approach 2:
The patent creates a composite coating system consisting of multiple layers with different functions: a YSZ thermal barrier layer for thermal protection, a bond coat layer for corrosion resistance, and potentially intermediate layers. This composite structure combines the thermal insulation properties of YSZ with the vanadium oxide resistance of the bond coat materials.
2Reliability
If MgO is added as fuel additive to inhibit vanadium species reaction, then corrosion resistance is improved, but complete protection is not achieved due to penetration through microcracks and porosity
Solution Approach 1:
The patent applies a bond coat layer in advance before applying the YSZ thermal barrier coating. This preliminary protective layer is designed to intercept and resist vanadium oxide attack before it can reach the substrate, providing a first line of defense that addresses the penetration issue through microcracks and porosity in the overlying YSZ layer.
Solution Approach 2:
The bond coat serves as an intermediary barrier between the corrosive environment (vanadium oxide penetrating through YSZ microcracks) and the substrate. It provides an additional protective interface that prevents direct attack on the substrate even when the YSZ layer becomes compromised.
3Temperature
If TBC system is used to increase operating temperature, then thermal performance is improved, but spallation resistance worsens due to thermal mismatch
Solution Approach 1:
The bond coat layer acts as an intermediary transition layer between the YSZ thermal barrier coating and the superalloy substrate. It is designed with intermediate thermal expansion properties that gradually transition from the substrate to the YSZ layer, reducing the abrupt thermal mismatch that causes spallation and improving overall system stability at elevated temperatures.
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 system effectively resists vanadium oxide attack, prolonging the operational life of turbine components and reducing maintenance downtime by preventing corrosion and spallation.
Implementation Method 1
A ceramic coating overlies the bond coat comprising a zirconium oxide stabilized by a cation of a rare earth element species
Implementation Method 2
V 2 O 5 is an acidic oxide that can leach yttria from YSZ in cracks and porosity that occur in such thermal barrier coatings
Implementation Method 3
a bond coat is applied between the TBC and the high temperature metal to reduce the thermal mismatch between the TBC and the high temperature metal
Implementation Method 4
The TBC increases the operating temperature of the high temperature substrate metal
Data Source
Figure 1~4
Figure 5~7
AI summary
A vanadium resistant coating system resistant to high temperature vanadium attack. The system comprises a high temperature superalloy substrate (10). A bond coat (20) overlies the superalloy substrate (10). The bond coat (20) may be applied in multiple layers. A ceramic coating (40) overlies the bond coat. The ceramic coating (40) further comprises a zirconium oxide stabilized by at least one cation selected from the group consisting of Yb3+, Lu3+, Sc3+ and Ce4+, in the amounts of about 5-10 weight percent. An overcoat may overlie the ceramic coating. The overcoat may be a sacrificial layer of YSZ infiltrated with cations having an atomic radius larger than Y3+. Alternatively, the overcoat may comprise zirconium oxide stabilized by Ce4+.