Brazing Ceramic Matrix Composite Parts Using Capillary Elements
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Solution Overview
Problem
Brazing of ceramic matrix composite materials is technically challenging due to insufficient breaking stress, particularly in shear forces, caused by high surface roughness and gas trapped in the solder joint, leading to weak connections and defects.
Innovation Solution
The method involves creating perforations on the assembly faces of composite material parts, inserting capillary elements and pins, and applying a solder composition that liquefies and distributes through capillarity, with a clearance for degassing and visual inspection to ensure uniform soldering, enhancing mechanical strength and anchoring of the brazed connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional brazing is used on CMC parts with high surface roughness, then the brazing process can be performed, but the solder distribution is poor creating zones of weakness in the connection
Solution Approach 1:
The method applies preliminary action by creating perforations in the CMC parts before brazing, and by using capillary elements (such as ceramic particles or fibrous substrates) that are pre-positioned on the assembly faces. These preparatory structures guide the molten solder flow and ensure uniform distribution before the actual brazing occurs, preventing zones of weakness in the final joint.
Solution Approach 2:
Capillary elements serve as intermediaries between the rough CMC surfaces and the solder. These elements (ceramic particles, fibrous substrates, or webs) create a controlled pathway for solder distribution, mediating the interaction between the irregular surfaces and the molten metal to achieve uniform coverage despite the high surface roughness of the CMC parts.
2Reliability
If conventional brazing is used without degassing pathways, then the brazing process is simpler, but gaseous species are trapped inside the solder joint creating porous defects
Solution Approach 1:
The method utilizes porous capillary elements (such as porous ceramic particles or fibrous substrates) that provide interconnected pathways for gas evacuation. These porous structures allow gaseous species generated during brazing to escape through the capillary network, preventing gas entrapment and porous defects in the final solder joint while maintaining structural integrity.
Solution Approach 2:
The brazing system is segmented into distinct functional zones: solidification zones where solder forms the joint, and degassing zones provided by the porous capillary elements where gases escape. This segmentation separates the conflicting requirements of forming a dense solder joint while allowing gas evacuation, improving reliability without excessive complexity.
3Strength
If the solder joint is made larger to compensate for weak connections, then more material is used, but the shear strength remains insufficient due to inherent connection weaknesses
Solution Approach 1:
The brazing system uses composite structures combining CMC parts with capillary elements (such as ceramic particle-solder composites or fibrous substrate-solder composites). This composite approach creates a multi-phase joint where the capillary elements reinforce the solder matrix, significantly improving shear strength through mechanical interlocking and distributed stress pathways, thereby achieving high strength with reduced solder quantity.
Solution Approach 2:
The method applies local quality by concentrating reinforcement features (perforations, capillary elements) at critical locations within the brazing joint rather than uniformly throughout. The capillary elements are strategically positioned to provide localized stress distribution and anchoring, achieving high shear strength in critical zones without requiring excessive solder material throughout the entire 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
This method significantly reinforces the shear strength of the brazed connection by anchoring the solder joint firmly within the material and prevents gas pocket formation, resulting in improved mechanical strength and reduced defects.
Implementation Method 1
heat treatment to liquefy the solder composition so as to distribute by capillarity the molten solder composition between the faces of assembly of the first and second parts made of composite material
Implementation Method 2
a clearance is provided between the internal wall of each perforation and the external wall of the pin inserted into the perforation. The presence of such a gap allows degassing during the brazing cycle, the gaseous species being evacuated by the end of the perforation(s) emerging outside the assembly faces
Data Source
Figure 1A~1B
Figure 1C~1E
Figure 2~3
AI summary
The invention relates to a method for the braze-assembly of a first part (10) and a second part (20) made from a composite material, said first and second parts (10, 20) each comprising an assembly face (10a, 20a) intended to be brazed to the assembly face of the other part. The method comprises the following steps: producing at least one perforation (101) in the assembly face of the first part (10); inserting capillary elements (30) between the assembly faces (10a, 20a) of the first and second parts (10, 20) made from composite material; positioning the first and second parts (10, 20) facing one another, with the insertion of a slug (5) in each perforation in the first part (10); placing a brazing composition (41) in contact with part of the capillary elements (30); liquefying the brazing composition (41) by means of heat treatment, such as to produce the capillary distribution of the molten brazing composition between the assembly faces of the first and second parts of composite material.