Silicon Transition Metal Bond Layer for Thermal Stress
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Solution Overview
Problem
High-temperature mechanical system components, such as ceramic or ceramic matrix composite substrates, face damage from chemical attack and mechanical failure due to differential thermal expansion and oxidation, especially when exposed to hot gases in gas-turbine engines.
Innovation Solution
A bond layer comprising silicon metal and transition metal carbides, borides, or nitrides is applied to the substrate, along with an overlying oxide layer, to match the coefficient of thermal expansion and enhance adherence, reducing stress and oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is applied to ceramic or CMC substrates, then oxidation resistance is improved, but mechanical failure occurs due to differential thermal expansion
Solution Approach 1:
A bond layer comprising silicon metal and transition metal carbide, boride, or nitride is introduced as an intermediary between the ceramic/CMC substrate and the oxide overlying layer. This bond layer serves as a mediator that reconciles the conflicting requirements of oxidation protection and thermal expansion compatibility, preventing mechanical failure while maintaining oxidation resistance.
Solution Approach 2:
The bond layer is formulated as a composite material combining silicon metal with transition metal carbide, boride, or nitride. This composite structure enables the bond layer to simultaneously achieve the desired coefficient of thermal expansion to match the substrate while maintaining adequate oxidation resistance and mechanical properties.
2Reliability
If an oxide overlying layer is added to protect against oxidation, then oxidation resistance improves, but stress increases due to CTE mismatch
Solution Approach 1:
The bond layer's coefficient of thermal expansion is specifically engineered to fall within a target range (5-13 ppm/°C) by adjusting the composition of silicon metal and transition metal carbide/boride/nitride. This parameter optimization ensures the bond layer acts as a stress-buffering intermediate between the substrate and oxide layer, reducing thermal stress during temperature cycling.
3Stability of the object's composition
If silicon metal is used in the bond layer, then CTE matching with substrate is improved, but oxidation resistance deteriorates
Solution Approach 1:
The bond layer combines silicon metal (which provides CTE matching with ceramic/CMC substrates) with transition metal carbide, boride, or nitride (which provide enhanced oxidation resistance and mechanical strength). This composite formulation balances the competing requirements of thermal expansion compatibility and oxidation resistance.
Solution Approach 2:
The bond layer is designed with specific compositional ranges: 60-95 wt% silicon metal for CTE matching, and 5-40 wt% transition metal carbide/boride/nitride for oxidation resistance and mechanical properties. This localized optimization of material composition at the substrate-coating interface resolves the contradiction between CTE matching and oxidation resistance.
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 solution effectively reduces mechanical failure and oxidation of the substrate by matching thermal expansion coefficients and improving the adherence and oxidation resistance of the coating, thereby enhancing the durability of high-temperature mechanical system components.
Implementation Method 1
Transition metal carbides, transition metal borides, and transition metal carbides may have a different coefficient of thermal expansion than silicon metal. For example, transition metal carbides and transition metal borides may have CTEs between about 5 parts per million per degree Celsius (ppm/° C.) and about 8 ppm/° C., and transition metal nitrides may have CTEs of about 9 ppm/° C.
Data Source
AI summary
In some examples, an article may include a substrate and a coating on the substrate. In accordance with some of these examples, the coating may include a bond layer and an overlying layer comprising at least one oxide. In some examples, the bond layer comprises silicon metal and at least one of a transition metal carbide, a transition metal boride, or a transition metal nitride.