Brazed Joint Between Titanium and Silicon Carbide Ceramic
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Solution Overview
Problem
The challenge lies in assembling titanium metal parts with silicon carbide or carbon ceramic parts through brazing, as their differing thermal expansion coefficients lead to significant stress and potential breakage, and existing methods fail to address chemical incompatibility and porosity issues at high temperatures.
Innovation Solution
A stacked structure is proposed, comprising a metal part, a deformable titanium spacer to accommodate expansion differences, a rigid spacer like aluminum nitride or tungsten to act as a chemical barrier, and a silver-based solder to ensure compatibility and mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct brazing is used between titanium metal and silicon carbide ceramic, then assembly is achieved, but strong stresses and chemical reactions cause breakage and porosity
Solution Approach 1:
The patent introduces a multi-layer intermediate structure consisting of a ductile metal layer and a rigid spacer layer between the titanium metal and silicon carbide ceramic. The ductile metal layer acts as a stress-absorbing intermediary that accommodates thermal expansion differences, while the rigid spacer layer serves as a chemical barrier preventing direct reaction between dissimilar materials, thus eliminating breakage and porosity issues
Solution Approach 2:
The patent employs a composite intermediate structure combining ductile metal and rigid ceramic spacer materials. This composite approach allows the intermediate layer to simultaneously provide stress accommodation through ductile deformation and chemical isolation through the rigid barrier, resolving the contradiction between ease of assembly and joint reliability
2Stability of the object's composition
If a rigid spacer with expansion coefficient close to ceramic is used, then chemical compatibility is improved, but expansion differential compensation is reduced
Solution Approach 1:
The patent divides the intermediate layer into two distinct functional segments: a ductile metal layer that handles thermal expansion compensation through deformation, and a rigid spacer layer that provides chemical compatibility and barrier functions. This segmentation allows each layer to specialize in one function without compromising the other
Solution Approach 2:
The patent applies different material properties to different layers of the intermediate structure: the ductile metal layer is optimized for stress accommodation with high ductility, while the rigid spacer layer is optimized for chemical stability and low thermal expansion. Each layer's local quality is tailored to its specific function, resolving the contradiction between chemical compatibility and stress management
3Stress or pressure
If ductile metal spacer is used to accommodate expansion, then stress compensation is improved, but chemical barrier function is reduced
Solution Approach 1:
The patent segments the intermediate structure into a ductile metal layer for stress compensation and a rigid spacer layer for chemical stability, allowing each layer to perform its specialized function without compromise
Solution Approach 2:
The rigid spacer layer acts as a chemical barrier intermediary between the ductile metal layer and the silicon carbide ceramic, preventing direct chemical interaction while allowing the ductile layer to perform its stress-accommodation function
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 configuration effectively compensates for thermal expansion differences, prevents undesirable chemical compound formation, and enhances the mechanical strength and durability of the assembly, achieving shear resistance comparable to or exceeding that of the ceramic material alone.
Implementation Method 1
a first spacer capable of deforming to accommodate an expansion differential between the metal part and the part made of ceramic material
Implementation Method 2
fulfilling a so-called 'chemical barrier' function allowing, on the one hand, avoid the migration of elements of the ceramic material (silicon carbide, carbon, etc.) towards the metal part or vice versa
Implementation Method 3
assembled two by two by brazing
Implementation Method 4
the known brazing techniques used for homogeneous ceramic/ceramic bonds
Implementation Method 5
the coefficient of expansion of such a metal alloy is approximately two to five times higher than that of ceramic materials. So for a typical 30mm assembly, a 0.2mm expansion offset must be recovered when cooling from the solidification temperature of the solder to the ambient temperature of that assembly
Data Source
Figure 1~2
AI summary
The invention relates to a brazed joint between a titanium-based metal part and a ceramic part based on silicon carbide (SiC) and/or carbon. The inventive joint comprises a stacked structure consisting of the following elements which are assembled in pairs by means of brazing, namely: the titanium-based metal part (10), a first spacer (11) which can deform in order to accommodate an expansion differential between the metal part (10) and a ceramic part (20) based on silicon carbide and/or carbon, a second rigid spacer (12) which has a similar expansion coefficient to that of the ceramic part (20) and which is made from aluminium nitride (AIN) or tungsten (W), and the ceramic part (20).