Additive manufacturing of copper-nickel alloys
Corrosion resistance and biofouling protection for the maritime industry and offshore applications.
1. Introduction: Salt water as the ultimate endurance test
Pure copper is the king of heat conduction, but too soft for structural applications. Pure nickel is extremely corrosion-resistant but conducts heat poorly. If both elements are alloyed, a family of materials is created that has been indispensable in the maritime industry (shipbuilding, offshore, desalination plants) for decades: copper-nickel alloys (CuNi).
The introduction of metal 3D printing (particularly PBF and WAAM) into shipping opens up the possibility of producing gigantic pump housings or complex heat exchangers made of CuNi at the push of a button - often directly on the high seas.
The magic of “bio-fouling”
Why is CuNi90/10 (90% copper, 10% nickel) often used for seawater pipes instead of stainless steel? Copper-nickel alloys release minimal copper ions into seawater. These ions prevent barnacles, mussels and algae from settling on the surface (bio-fouling). Stainless steel pipes would immediately grow over in seawater, CuNi stays clean.
2. Challenges in the PBF-LB powder bed
In Laser Powder Bed Fusion (PBF-LB), the processing of CuNi powders (usually CuNi70/30 or CuNi90/10) brings with it specific hurdles.
- Reflectivity: The copper in the alloy strongly reflects infrared lasers. The nickel helps massively here: it absorbs energy much better than pure copper and ensures that the alloy can be melted much more stably than pure copper. A normal fiber laser is often sufficient to process CuNi excellently.
- Thermal cracking: In contrast to pure aluminum or titanium, CuNi often has a wide solidification interval. This means the metal goes through a prolonged "doughy" state as it cools, which theoretically makes it susceptible to hot tearing. Precise laser parameters are crucial.
3. Wire Arc Additive Manufacturing (WAAM) for shipbuilding
When it comes to gigantic ship propellers or pump housings weighing tons, the powder bed is ruled out due to the limited installation space. This is the hour of WAAM (wire arc printing).
- CuNi welding wire is standardized worldwide and extremely cheap (compared to metal powder).
- A robot arm welds the CuNi wire layer by layer. Since CuNi has been well understood in welding technology for decades (good weldability), WAAM delivers outstanding results with enormous build-up rates (several kilograms per hour).
4. On-demand spare parts on the high seas
The Royal Navy and the US Navy are increasingly equipping their aircraft carriers and escort ships with metal 3D printers. The goal is clear: the digital spare parts warehouse.
If the housing of a desalination pump breaks in the middle of the Pacific, it takes weeks until a casting is delivered. With an AM system on board, the engineer downloads the CAD file and prints the spare part (e.g. made of highly resistant CuNi) directly on the ship in a few hours. This is revolutionizing the logistics chains of global shipping.
5. Conclusion: A classic goes digital
Copper-nickel is not an exciting space superalloy, but a rock-solid, industrial endurance runner. Its outstanding resistance to salt water corrosion and biofouling makes it the undisputed standard in maritime technology. Additive manufacturing is now bringing this classic into the 21st century by dramatically shortening supply chains for massive replacement parts and paving the way for in-situ repairs on the oceans.