Gradient Bonding Material for Ceramic-Metal Gas Turbine Joints
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Solution Overview
Problem
Securing ceramic components to metallic structures in gas turbine engines is challenging due to differential thermal expansion and elasticity, leading to shear stresses that can cause detachment, especially when using ceramic matrix composites that are relatively low in strength compared to metals.
Innovation Solution
A bonding material comprising refractory elements with varying shear moduli, arranged in order of increasing modulus, is used to secure ceramic components to metallic components, employing transient liquid phase or partial transient liquid phase bonding to withstand shear stresses, with specific refractory elements like europium, ytterbium, and hafnium selected based on the materials' properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic components are attached to metallic structures using typical attachment configurations, then the structural integrity is maintained, but the differential thermal expansion and elasticity cause shear stresses leading to detachment
Solution Approach 1:
A bonding material comprising multiple layers of refractory elements with progressively varying shear moduli is introduced as an intermediary between the ceramic component and metallic structure. This gradient bonding material transitions from lower shear modulus near the ceramic to higher shear modulus near the metal, accommodating differential thermal expansion and reducing shear stresses that cause detachment.
Solution Approach 2:
The bonding material utilizes controlled changes in material parameters (shear modulus) across its thickness by selecting refractory elements in order of increasing shear modulus. This parameter gradient allows the bonding material to adapt to the varying mechanical properties of the ceramic and metal components, reducing thermal mismatch stresses.
2Productivity
If exotic metallic alloys are used without active cooling, then engine efficiency is improved, but the materials cannot withstand extreme temperatures within the engine
Solution Approach 1:
The bonding material is composed of multiple refractory elements (such as molybdenum, tungsten, rhenium, tantalum, niobium, and hafnium) arranged in layers with increasing shear modulus. This composite structure combines the advantages of different refractory materials to achieve both high-temperature tolerance and mechanical compatibility with ceramic components.
3Loss of energy
If ceramic matrix composites are used, then cooling requirements are reduced, but the relatively low strength compared to metals makes typical attachment configurations unusable
Solution Approach 1:
The bonding material exhibits spatially varying properties with different layers having different shear moduli. The lower shear modulus layers are positioned adjacent to the ceramic component to accommodate its lower strength, while higher shear modulus layers are positioned near the metallic structure to provide adequate mechanical support and stress transfer.
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 mitigates thermally induced strains and shear stresses, ensuring a stable bond between ceramic and metallic components, thereby enhancing the durability and efficiency of gas turbine engine components by allowing higher operating temperatures without active cooling.
Implementation Method 1
The bonding material includes at least one of a transient liquid phase bond and a partial transient liquid phase bond
Data Source
Figure 1
Figure 2~3C
AI summary
A gas turbine engine component assembly includes a ceramic component having a first thermal characteristic. A metallic component has a second thermal characteristic. A bonding material secures the ceramic component to the metallic component. The bonding material includes at least one of a transient liquid phase bond and a partial transient liquid phase bond. The bonding material is configured to withstand a shear stress parameter relating to a differential between the first and second thermal characteristics.