Silver-Graphite Contact Brazing With Active Carbide-Forming Interlayers
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Solution Overview
Problem
Conventional braze alloys fail to form bonds with graphite in silver-graphite contacts, resulting in joints with low strength and high electrical resistance, and existing methods to address this issue, such as decarburizing or adding additional layers, increase costs and complexity.
Innovation Solution
A two-step process involving coating silver-graphite contacts with a braze containing Ti, Hf, Zr, Cr, Si, or V, along with Cu, at controlled temperatures and oxygen-free environments, followed by direct brazing to copper carriers, forming metal carbides that enhance adherence and wetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional braze alloys (Cu-Ag-P) are used to join silver-graphite contacts, then the braze can be applied and processed, but the braze does not bond with the graphite, resulting in low joint strength and high electrical resistance
Solution Approach 1:
The invention changes the chemical composition parameters of the braze alloy by incorporating active elements (Ti, Hf, Zr, Cr, Si, or V) in specific amounts (0.1-10 wt.%) alongside Cu (20-60 wt.%) and Ag (20-60 wt.%). This compositional modification enables the braze to chemically react with graphite, forming strong bonds and reducing electrical resistance, thereby resolving the contradiction between joint strength and electrical resistance.
Solution Approach 2:
The invention creates a composite braze material that combines conventional braze components (Cu, Ag) with active carbide-forming elements (Ti, Hf, Zr, Cr, Si, V). This composite structure allows the braze to simultaneously provide good wetting properties and form strong chemical bonds with graphite, achieving both low electrical resistance and high joint strength.
2Ease of manufacture
If decarburizing heat treatment is applied to remove graphite, then a porous Ag layer is formed that can be wetted by braze, but additional processing steps are required and the contact loses reinforcement
Solution Approach 1:
The invention enables the braze to directly bond with graphite in the silver-graphite contact without requiring pre-treatment to remove graphite. The active elements in the braze self-react with the graphite during the brazing process, forming strong carbide bonds. This eliminates the need for decarburizing steps while preserving the reinforcing graphite, thereby improving ease of manufacture and maintaining contact strength.
Solution Approach 2:
The invention performs the bonding action preliminarily by designing a braze composition that is pre-capable of reacting with graphite. The active elements are incorporated into the braze formulation in advance, so that during the normal brazing process, the chemical reaction with graphite occurs automatically, eliminating the need for separate graphite removal and reapplication steps.
3Ease of manufacture
If a silver layer is added to the contact surface, then the braze can wet the surface, but the layer does not contribute to useful contact volume and increases material cost
Solution Approach 1:
The invention makes the braze alloy itself multi-functional by incorporating active elements that enable it to both wet the silver surface and chemically bond with the graphite. This eliminates the need for a separate silver layer, as the braze directly performs both functions: providing wetting capability and forming strong bonds with the graphite reinforcement, thereby preserving useful contact volume and reducing material cost.
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 process achieves strong, low-resistance joints without additional processing steps, suitable for industrial applications, by ensuring graphite is not oxidized and forming stable metal carbides that enhance bonding.
Implementation Method 1
the active braze is applied to the silver-graphite contact... whereby the step of applying is performed prior to the application of heat for brazing... the braze contains one or several of Ti, Hf, Zr, Cr, Si and/or V... forming metal carbides that enhance adherence and wetting
Implementation Method 2
coating the silver-graphite contact with a braze at a temperature of at least the solidus temperature of the braze minus 100 K... followed by direct brazing to copper carriers
Implementation Method 3
conventional braze alloys... wet only the metallic part of the contact... forming metal carbides that enhance adherence and wetting
Data Source
Figure 1
AI summary
Process of directly connecting a silver-graphite contact with a copper carrier comprising the preparation of an intermediate under controlled conditions.