Boron-Doped Refractory Compound for TGO Crystallization Control
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Solution Overview
Problem
Current environmental barrier coatings (EBCs) for ceramic components in high-temperature gas turbine engines face limitations due to the low melting point of silicon bond coats, leading to thermally grown oxide (TGO) crystallization and subsequent spall, which restricts the operational temperature and durability of the coatings.
Innovation Solution
A boron-doped refractory compound with the formula Ln3-xBxM5-yByO12 is integrated into a silicon-based bond coating, where Ln comprises rare earth elements and M includes Ga, In, Al, or Fe, to prevent TGO crystallization and maintain the oxide in an amorphous phase, thereby enhancing the operational temperature and durability of the coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon bond coat is used in environmental barrier coatings, then oxidation of the substrate is prevented and a passive silicon oxide scale forms, but the upper operational temperature is limited due to the low melting point of silicon metal
Solution Approach 1:
The patent applies composite materials by combining silicon-based compounds with boron-doped rare earth metal oxide compounds in a multilayer coating structure. The silicon bond coat provides oxidation protection while the boron-doped rare earth metal oxide layer prevents TGO crystallization and enables higher operational temperatures, resolving the contradiction between oxidation protection and temperature resistance.
Solution Approach 2:
The patent changes the chemical composition parameters of the bond coat by incorporating boron (B) at specific concentrations (0.001-10 wt%) and using rare earth metal oxides (Ln3-xBxM5-yByO12) to modify the phase transformation behavior of the thermally grown oxide. This prevents crystallization at higher temperatures while maintaining the protective amorphous oxide scale.
2Productivity
If the operational temperature is increased to improve engine efficiency, then productivity increases, but TGO crystallization occurs leading to coating spall and reduced durability
Solution Approach 1:
The patent modifies the chemical composition by adding boron-doped rare earth metal oxide compounds that change the phase transformation temperature of the TGO. This parameter change allows the coating to withstand higher operational temperatures without crystallization-induced spall, maintaining durability while enabling improved engine efficiency.
Solution Approach 2:
The boron-doped rare earth metal oxide compound acts as an intermediary layer between the silicon bond coat and the environmental barrier coating. It mediates the thermal stress and prevents direct crystallization of the TGO, allowing higher temperature operation without coating failure.
3Object-affected harmful factors
If rare earth silicate compounds are used as EBC materials, then water vapor penetration is prevented, but oxygen penetration occurs causing substrate oxidation and blistering
Solution Approach 1:
The patent segments the coating system into distinct functional layers: a silicon bond coat that provides oxidation protection and forms a passive oxide scale, and a rare earth silicate EBC layer that provides water vapor barrier properties. This segmentation allows each layer to specialize in preventing different harmful factors without compromising the other.
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 boron-doped refractory compound inhibits TGO crystallization, maintaining the oxide in an amorphous state at higher temperatures, preventing spall and extending the operational temperature limit of the silicon-based bond coating and EBC, while also limiting oxide scale growth.
Implementation Method 1
the boron-doped refractory compound inhibits TGO crystallization, maintaining the oxide in an amorphous state at higher temperatures
Implementation Method 2
Silicon carbide and silicon nitride ceramics undergo oxidation in dry, high temperature environments. This oxidation produces a passive, silicon oxide scale on the surface of the material.
Data Source
AI summary
A compound is generally provided that has the formula: Ln3-xBxM5-yByO12, where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1.5; M comprises Ga, In, Al, Fe, or a combination thereof; y is 0 to about 2.5; and x+y is greater than 0. A composition is also provided that includes a silicon-containing material (e.g., silicon metal and/or a silicide) and the boron-doped refractory compound having the formula described above, such as about 0.001% to about 85% by volume of the boron-doped refractory compound.