Direct Brazing Surface Preparation for Low-Temperature Carbon Joints
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Solution Overview
Problem
Existing methods for brazing carbon-based parts with metal parts require high temperatures, leading to thermomechanical stresses and material damage, and involve complex processes like fluxing and ultrasonic vibrations, which are not suitable for certain applications.
Innovation Solution
A method involving plasma treatment to create an active surface on carbon or metal parts, followed by deposition of a carbide-forming element layer and a protective gold layer, allowing direct brazing at temperatures below 450°C without intermediate materials or fluxing, using non-active solders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature brazing (>800°C) is used to join carbon-based parts with metal parts, then strong joints are achieved, but thermomechanical stresses and material damage occur
Solution Approach 1:
The surface of the carbon-based part is preliminarily treated by plasma cleaning and coating with a carbide-forming element (Ti, Cr, or Zr) before brazing. This preliminary surface preparation enables strong adhesion at low temperatures, resolving the contradiction by achieving joint strength without requiring high temperatures that cause thermomechanical stresses
Solution Approach 2:
The invention changes the brazing temperature parameter from conventional high temperatures (>800°C) to low temperatures (200-450°C). This parameter change is made possible by the surface treatment that creates an active surface with carbide-forming elements, allowing strong joints to form at lower temperatures and thus avoiding thermomechanical stress damage
2Object-affected harmful factors
If low temperature brazing (<700°C) is used to avoid material damage, then thermomechanical stresses are reduced, but complex processes like fluxing and ultrasonic vibrations are required
Solution Approach 1:
The complex fluxing and ultrasonic vibration steps are eliminated by performing preliminary surface treatment with plasma cleaning and carbide-forming element coating. This preliminary action creates an active surface that enables direct wetting by non-active solders at low temperatures without requiring additional complex processes
Solution Approach 2:
The carbide-forming element coating (Ti, Cr, or Zr layer) acts as an intermediary between the carbon-based part and the non-active solder. This intermediate layer facilitates adhesion and wetting at low temperatures without requiring flux or ultrasonic vibrations, thus simplifying the overall process while maintaining low thermomechanical stresses
3Object-affected harmful factors
If non-active solders are used at low temperatures, then material damage is avoided, but surface preparation is required to ensure good wetting
Solution Approach 1:
The surface is preliminarily prepared through plasma cleaning and coating with carbide-forming elements, creating an active surface that ensures good wetting by non-active solders. This preliminary action enables the use of non-active solders at low temperatures without requiring complex or time-consuming surface preparation steps during the brazing process itself
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
Enables strong, durable joints with reduced thermomechanical stresses, suitable for parts of varying dimensions, and eliminates the need for high-temperature annealing or ultrasonic vibrations, ensuring good mechanical strength and long service life.
Implementation Method 1
carrying out a plasma treatment with a neutral gas, on the part, whereby the part is cleaned and an active surface is formed over the part
Implementation Method 2
depositing a first layer of an active element (called the adhesion layer) over the active surface of the part
Implementation Method 3
depositing a second layer made of gold over the first layer, whereby the first layer is protected from oxidation
Implementation Method 4
assembling the part with another part at an assembly temperature lower than 450° C.
Data Source
AI summary
A method for joining, by brazing, a first part and a second part, the steps of preparing at least one of the parts including the following: a) providing a part intended to be brazed, the part being made of carbon or based on titanium, nickel or a CoCr alloy, b) performing inert gas plasma treatment on the part whereby the part is cleaned and an active surface is formed on the part, c) depositing a first layer comprising an active element on the active surface of the part, the active element being a carbide-forming element, d) depositing a second layer of gold on the first layer, whereby the first layer is protected from oxidation and good wetting is ensured.