Age-Hardenable Copper Alloy Diffusion Bonding With Low Oxide Inclusions
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Solution Overview
Problem
Diffusion bonding of copper alloys is challenging due to strong oxide films that are difficult to remove and can re-form during the bonding process, resulting in inadequate bonding strength and texture, especially when subjected to severe thermal shock or dimensional fluctuations.
Innovation Solution
Selectively using an age-hardenable copper alloy with a beryllium content of 0.7% by weight or less, ensuring a flat and oxide-free bonding surface, and performing diffusion bonding followed by homogenization, solution annealing, and aging treatments to reduce inclusion ratios and achieve high bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffusion bonding is performed on copper alloy with simple pressure reduction and temperature increase, then bonding process is simple, but oxide film cannot be removed and bonding strength is insufficient
Solution Approach 1:
The oxide film removal step is performed before diffusion bonding to prepare the bonding surfaces in advance. This preliminary action ensures that when bonding occurs, the surfaces are free from oxide contamination, enabling strong bonding without requiring complex in-situ removal mechanisms during the bonding process itself.
Solution Approach 2:
The patent employs a high vacuum environment (1×10^-4 Pa or lower) during diffusion bonding to prevent oxide film reformation. This inert atmosphere approach maintains oxide-free bonding surfaces throughout the bonding process, ensuring strong bonding strength while keeping the process relatively simple.
2Strength
If oxide film is removed before bonding, then bonding strength can be improved, but oxide film re-forms during temperature increase under high vacuum
Solution Approach 1:
The patent maintains a high vacuum environment (1×10^-4 Pa or lower) throughout the diffusion bonding process to prevent oxide film reformation. This controlled inert atmosphere ensures that once the oxide film is removed, it cannot re-form during the temperature increase phase, maintaining surface stability.
Solution Approach 2:
The patent carefully controls the heating rate and holding temperature parameters during diffusion bonding. By optimizing these parameters, the process achieves bonding at temperatures sufficient for diffusion without creating conditions that would promote oxide reformation, thus maintaining composition stability.
3Strength
If solution annealing and aging treatment are performed on diffusion-bonded copper alloy, then material strength is improved, but bonding part breaks due to insufficient bonding strength
Solution Approach 1:
The oxide film removal is performed as a preliminary step before diffusion bonding to ensure strong initial bonding. This preliminary preparation prevents oxide interference during subsequent heat treatments, allowing the bonding joint to withstand solution annealing and aging processes without failure.
Solution Approach 2:
The high vacuum environment maintained during diffusion bonding creates a stable, oxide-free bonding interface that can withstand subsequent thermal processing. This inert environment ensures the bonding joint maintains its integrity during solution annealing and aging treatments that would otherwise cause breakdown.
4Strength
If beryllium copper alloy with high beryllium content is used, then tensile strength and thermal conductivity are improved, but oxide film becomes stronger and harder to remove
Solution Approach 1:
The patent uses a high vacuum environment (1×10^-4 Pa or lower) to remove oxide films from beryllium copper alloy surfaces. This inert atmosphere approach effectively removes even the strong oxide films formed by high beryllium content alloys, enabling subsequent strong diffusion bonding without requiring excessive mechanical or chemical removal efforts.
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 approach results in a copper alloy bonded body with an extremely high bonding strength, capable of withstanding solution annealing and aging treatments without breaking at the bonding part, and exhibiting superior hydrogen-embrittlement resistance and thermal conductivity.
Implementation Method 1
diffusion bonding is widely known in which an oxide film of the surface layer is removed by sublimation in a pressure reducing and temperature increasing process to a bonding temperature, and pressure for adhesion is applied to a bonding part at a high temperature equal to or lower than the melting point to bond the stainless steel sheets
Implementation Method 2
an oxide film of the surface layer is removed by sublimation in a pressure reducing and temperature increasing process to a bonding temperature
Implementation Method 3
to realize a copper alloy member having an extremely high strength required in uses of the above-described heat exchanger for high pressure, solution annealing and an aging treatment need to be performed on an age-hardenable copper alloy
Implementation Method 4
solution annealing and an aging treatment need to be performed on an age-hardenable copper alloy
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
There is provided a bonded body of an age-hardenable copper alloy which has realized an extremely high bonding strength. This copper alloy bonded body is composed of a plurality of members made of an age-hardenable copper alloy, the members diffusion-bonded to one another. In the copper alloy bonded body, a bonding interface between the members remains, and (i) the age-hardenable copper alloy is a beryllium copper alloy of which the beryllium content is 0.7% by weight or less, and an area ratio of inclusions composed of an oxide, a carbide, and/or an intermetallic compound in a HAADF-STEM image of a rectangular section of a size of 800 nm in long side × 400 nm in short side including the bonding interface is 7.5% or less, or (ii) the age-hardenable copper alloy is a copper alloy free from beryllium, and an area ratio of inclusions composed of an oxide, a carbide, and/or an intermetallic compound in a HAADF-STEM image of a rectangular section of a size of 800 nm in long side × 400 nm in short side including the bonding interface is 30% or less.