Low-Beryllium Copper Alloy Diffusion Bonding for Thermal Shock
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Solution Overview
Problem
Existing diffusion bonding methods for copper alloys struggle to achieve high bonding strength due to strong oxide films that are difficult to remove and reform during the bonding process, leading to issues with thermal shock and dimensional fluctuations.
Innovation Solution
Selectively using an age-hardenable copper alloy with a beryllium content of 0.7% by weight or less, finishing the bonding surfaces to a predetermined flatness to remove the oxide film, and performing diffusion bonding followed by homogenization treatment, solution annealing, and aging treatment to achieve a high bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If diffusion bonding is performed on copper alloy in a similar step to stainless steel, then bonding is achieved, but bonding strength is insufficient and the bonded body breaks under thermal shock
Solution Approach 1:
The oxide film on the copper alloy surface is removed in advance by finishing the bonding surface to a predetermined flatness before diffusion bonding. This preliminary removal of oxide film prevents re-oxidation during bonding and ensures strong, reliable bonding that can withstand thermal shock and dimensional fluctuations.
2Ease of manufacture
If simple pressure reduction and temperature increase is used to remove oxide film, then the process is simple, but the strong oxide film on copper alloy is not easily removed
Solution Approach 1:
The bonding surface is finished to a predetermined flatness before diffusion bonding to remove the oxide film in advance. This preliminary surface preparation ensures effective oxide film removal without requiring complex processes during the bonding operation itself.
3Strength
If oxide film is removed before bonding, then bonding strength improves, but oxide film reforms on bonding surface during temperature increase under high vacuum
Solution Approach 1:
The oxide film is removed by finishing the bonding surface to a predetermined flatness before bonding. The surface is prepared in advance with proper flatness (0.1mm or less over 100mm length) to prevent re-oxidation during the bonding process under high vacuum and temperature increase.
Solution Approach 2:
Diffusion bonding is performed under high vacuum conditions to create an inert environment that prevents re-oxidation of the copper alloy bonding surfaces during temperature increase. The high vacuum atmosphere protects the freshly prepared bonding surfaces from oxide formation.
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 severe thermal shock and dimensional fluctuations, while maintaining the hydrogen-embrittlement-resistant properties and high thermal conductivity required for applications like heat exchangers in hydrogen stations.
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
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
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, wherein a bonding interface between the members remains. In the copper alloy bonded body, the content of beryllium in the age-hardenable copper alloy is 0.7% by weight or less, and, in a laser microscope image of a section including the bonding interface, a ratio of a total length of a line segment corresponding to a discontinuous region relative to an entire length of a bonding interface line defined along the bonding interface and a position where the bonding interface was present is 3.5% or more. The discontinuous region is defined as a region where, when a plurality of perpendicular lines is drawn with respect to the bonding interface line at a pitch of 5 µm, three or more adjacent perpendicular lines do not intersect with the remaining bonding interface.