Beryllium Copper Bonding With Thin Nickel Layer to Prevent Voids
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Solution Overview
Problem
Beryllium copper alloys used in heat exchangers for hydrogen stations face challenges in achieving high bonding reliability due to the formation of Kirkendall voids and cracks during diffusion bonding and subsequent heat treatments, which affect the airtightness and watertightness of the bonded body.
Innovation Solution
A beryllium copper alloy bonded body is created using a nickel layer with a thickness of 8 μm or less, which facilitates bonding and subsequent heat treatments such as solution annealing and aging, thereby preventing the accumulation of beryllium at crystal grain boundaries and reducing the occurrence of Kirkendall voids and cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If diffusion bonding is performed on beryllium copper alloy with a strong oxide film, then bonding between metal sheets is achieved, but high bonding strength close to the strength of the mother material cannot be obtained due to the difficult-to-remove oxide film
Solution Approach 1:
The oxide film on the beryllium copper alloy bonding surface is removed by sandblasting or shot blasting treatment before diffusion bonding. This preliminary action eliminates the obstacle (oxide film) that would otherwise prevent high bonding strength, allowing the bonding process to proceed without interference from the difficult-to-remove oxide layer.
2Reliability
If a nickel layer is used to facilitate diffusion bonding of beryllium copper alloy, then adhesion between bonding surfaces is improved, but Kirkendall voids and cracks occur during subsequent solution annealing, affecting airtightness and watertightness
Solution Approach 1:
The thickness of the nickel layer is precisely controlled within the range of 0.01 to 0.06 times the sheet thickness, with a preferred range of 0.02 to 0.05 times. This parameter optimization prevents excessive nickel diffusion into the beryllium copper alloy during solution annealing, thereby avoiding the formation of Kirkendall voids and cracks while maintaining adequate adhesion.
Solution Approach 2:
The nickel layer is applied only on the bonding surfaces of the beryllium copper alloy sheets, providing localized adhesion enhancement exactly where needed. This localized treatment facilitates diffusion bonding at the interface without causing harmful effects in the bulk material during subsequent heat treatment.
3Strength
If the nickel layer thickness is increased to improve adhesion, then bonding between different metals is facilitated, but accumulation of beryllium at crystal grain boundaries increases, leading to more Kirkendall voids
Solution Approach 1:
The nickel layer thickness is optimized to a specific range (0.01 to 0.06 times sheet thickness) that balances two competing requirements: providing sufficient adhesion strength for diffusion bonding while limiting the amount of nickel present to prevent excessive beryllium accumulation and Kirkendall void formation during solution annealing.
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 beryllium copper alloy bonded body with high bonding reliability and improved airtightness/watertightness, suitable for use in heat exchangers, particularly in hydrogen stations, by controlling the nickel layer thickness to prevent defects during diffusion bonding and heat treatment.
Implementation Method 1
diffusion bonding, performed by removing an oxide film on a surface layer by sublimation in a heating process to a bonding temperature under reduced pressure, and bonding stainless steel sheets by applying contact pressure to a bonding part under a high temperature of a melting point or lower
Implementation Method 2
removing an oxide film on a surface layer by sublimation in a heating process to a bonding temperature under reduced pressure
Implementation Method 3
performing a solution annealing on the intermediate bonded body
Implementation Method 4
performing an aging treatment on the intermediate bonded body to which the solution annealing has been performed
Data Source
AI summary
Provided is a beryllium copper alloy bonded body including a first member made of a beryllium copper alloy and a second member made of a beryllium copper alloy, wherein the first member and the second member are bonded to each other via the nickel layer having a thickness of 8 μm or less.