New method of 3D printing metals and alloys

ENGINEERS from the US’ Northwestern University have devised a method of using 3D printing technology to produce metals and alloys from rust and metal powders.

The team’s method involves creating liquid inks from metals or mixed metal powders. They are dissolved in solvents and elastomeric polymer is added to allow the printed layers to stick together. By feeding the dense liquid through a syringe, the ink can be dispensed through multiple nozzles at room temperature.

Once the structure is printed, the mixture instantly solidifies with the previous layers the structure, called a “green body,” which is flexible due to the elastic polymer binder containing unbonded metallic powders.

The team can shape the material before fusing the final structure in a furnace – using sintering, which fuses the metals without melting them – to create the large final structures that sinter uniformly without warping or cracking.

David Dunand, professor of materials science and engineering at Northwestern, said, “As a metallurgist, I'm amazed that the structure does not deform or break apart, despite shrinking extensively during densification. That is not something that I see often.”

Conventional methods of printing metallic structures use metal powder beds and expensive lasers or electron beams, where layers of powder are fused together at high energy to create a 3D object.

This method has previously prevented certain types of chemical architecture to form. The team claims its liquid method gives greater control over the shape of the structures created. They also say the method will be easier to scale up an industrial level, and that the structures are only limited to the size of the furnace available.

Ramille Shah, assistant professor of materials science and engineering at Northwestern, said, “This is exciting because most advanced manufacturing methods being used for metallic printing are limited as far as which metals and alloys can be printed. Our method greatly expands which metals we're able to print, which opens up a lot of different applications.”

The team has been able to print metal oxides, such as rust, which can then be reduced into iron. The team discovered that they could 3D print structures with rust and other metallic oxides first, and then use hydrogen to convert the green bodies into the respective metal before sintering.

“It might seem like we are complicating things by adding a third reduction step where we turn rust into iron, but this opens up possibilities for using very cheap oxide powders rather than expensive metal powders. It's hard to find something cheaper than rust,” Dunand added.

The team believes its printing method can have many industrial applications including printing batteries, solid-oxide fuel cells and medical implants, mechanical parts for rockets and aircraft, and on-site manufacturing.

Advanced Functional Materials, DOI: 10.1002/adfm.201503921