Graded Composite Transition Joint for CTE Mismatch Relief
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Solution Overview
Problem
Advanced ultra-supercritical (A-USC) power plants face challenges with dissimilar metal weldments (DMWs) due to thermal stresses caused by coefficient of thermal expansion (CTE) mismatch, leading to premature failure under cyclic operating conditions.
Innovation Solution
Additively manufactured graded composite transition joints (AM-GCTJs) are developed to address the CTE mismatch issue by creating a functionally graded composite transition joint with a gradual change in alloy composition, reducing stress concentrations and improving creep and thermal fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dissimilar metal weldments are used to connect different alloys in A-USC systems, then the system can achieve the required material properties for high temperature and pressure service, but thermal stresses caused by coefficient of thermal expansion mismatch lead to premature failure under cyclic operating conditions
Solution Approach 1:
The patent applies local quality by creating a functionally graded composite transition joint where the material composition varies spatially. The transition joint contains a gradient of alloy compositions ranging from Grade 91 steel through intermediate compositions to austenitic stainless steel, allowing each local region to have properties optimized for its specific thermal and mechanical environment, thereby reducing thermal stress concentrations at the interface
Solution Approach 2:
The patent employs composite materials by manufacturing a transition joint that is a composite structure combining Grade 91 steel and austenitic stainless steel in a graded configuration. This composite transition joint integrates the high creep strength of Grade 91 steel with the oxidation resistance of austenitic stainless steel, while the graded composition mitigates thermal expansion mismatch
2Ease of manufacture
If conventional welding processes are used for dissimilar metal weldments, then the manufacturing process is simple and cost-effective, but the weldments exhibit poor resistance to thermal creep fatigue and cracking
Solution Approach 1:
The patent applies parameter changes by utilizing additive manufacturing technology to fundamentally change the compositional parameter of the transition joint. Instead of a sharp interface between dissimilar metals, the additive process enables continuous variation of alloy composition parameters, creating a gradient structure that improves thermal creep fatigue resistance while maintaining manufacturing feasibility through digital design and automated deposition
3Device complexity
If a sharp interface between dissimilar metals is used in weldments, then the manufacturing process is straightforward, but stress concentrations occur at the interface leading to premature failure
Solution Approach 1:
The patent replaces the sharp interface with a graded composition structure where each local region has progressively changing material properties. This local quality approach creates a smooth transition in thermal expansion coefficients and mechanical properties, eliminating stress concentration points while maintaining structural integrity
Solution Approach 2:
The patent applies the concept of curvature by creating a smooth, continuous gradient in material composition rather than a sharp angular interface. This curved transition in properties reduces stress concentrations by eliminating abrupt changes in thermal and mechanical characteristics across the joint
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 AM-GCTJs effectively mitigate thermal stresses and improve the cracking and thermal creep fatigue resistances of DMWs, thereby enhancing the service life and performance of A-USC power plant components.
Implementation Method 1
thermal stresses caused by coefficient of thermal expansion (CTE) mismatch
Implementation Method 2
creep strength
Implementation Method 3
thermal fatigue strength
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4C
AI summary
A method for producing an additively manufactured, graded composite transition joint (AM-GCTJ) (300) includes preparing a grating or lattice pattern (101) from a first alloy A (100); the grating or lattice pattern (101) includes pores (110) in the grating or lattice patterns (101). The grating pattern is built from a first end to a second end being denser on the first end than on second end, and gradually reduces density by increasing the pore size and/or reducing density of the grating or lattice pattern; adding a second alloy B (200) powder to the second end of grating or lattice pattern. The second alloy B (200) powder is filled towards the first end. A composite is formed of first alloy A (100) and second alloy B (200) powder in the AM-GCTJ (300). The composite is subjected to hot isotropic pressing (HIP) to densify the composite. The second alloy B (200) is graduated from the first end to the second end of AM-GCTJ (300).