Structural metals used in construction, which require mining, refining, and processing, are responsible for emitting three billion tons of CO2-equivalent emissions. While recycling can reduce their environmental impact, fractures often prevent them from extending their lifespan.
Brazing and welding have been used for metal repair for thousands of years, but they have limitations. Some alloys are prone to cracking under extreme heat, and some complex 3D printed structures are inaccessible.
However, a team of researchers led by James Pikul has developed a new technique called “electrochemical healing” that can restore metals’ strength and toughness. They have successfully used this technique to repair fractured metals in steel, aluminum alloys, and complex 3D printed structures at room temperature.
According to Pikul, metals that are difficult to repair often end up as waste, which is problematic for both the environment and the economy. However, this new technique offers a sustainable solution that enables the full recovery of the metal’s tensile strength, including “unweldable” aluminum alloys used in aerospace.
The lead author of the paper, Zakaria H’sain, explains that their technique is different from brazing and welding. Rather than sealing the weakened site with filler material or melting two pieces of metal together, their technique uses electrochemical healing to repair the metal.
A new technique has been developed by a team of researchers led by James Pikul from the School of Engineering and Applied Science to restore the strength and toughness of fractured metals. The research team has named this method “electrochemical healing,” which uses a one-size-fits-all approach that can repair various metallic materials, including steel, aluminum alloys, and complex 3D printed structures, under room-temperature conditions.
To allow the metal to heal, the researchers placed it in an electrolyte, which was a salty water mixture containing nickel ions, and applied a negative voltage. This led to a chemical reaction called a reduction, which turned ions into solid metal atoms, healing the fracture. A protective polymer coating was applied to the metal to limit the nickel plating to the fracture site and not interfere with any other parts of the metal structure.
The team developed a model to gauge the efficacy of their repairs in restoring mechanical strength based on the geometry of the fracture, the original strength of the overall structure, the strength of the nickel coating, and other process parameters. The model was applied to three different alloys, and electrochemical healing recovered 100% of the strength for all those alloys.
The team collaborated with Masoud Akbarzadeh, assistant professor of architecture in the Stuart Weitzman School of Design, and a graduate student in Akbarzadeh’s Polyhedral Structures Laboratory to test electrochemical healing’s efficacy in repairing 3D printed efficient structures. The team plans to expand upon their work by designing and fabricating components that factor repairs needed beforehand and investigating methods of autonomous repair and reducing costs with alternative electrodeposited metals in future research.
Source: University of Pennsylvania