Despite the nonmagnetic nature of the constituent materials, the alloy exhibits magnetic properties
3D printing tends to use one homogeneous material or mixture throughout the entire item produced. By varying the composition from one part of the item to another, it could be endowed with properties that continuously change.
An example of this would be a rod made of an alloy of two metals whose ratio changes from 100% metal A to fifty-fifty, to 100% metal B, and so on.
Provided that the metals in question mix well, without giving rise to defects, the rod’s gradient properties — including magnetic ones — could be technologically useful, for example, for motor rotors, strips for magnetic encoders, or transformators.
The researchers produced such an alloy. Its two components — the metals A and B above — are themselves alloys: aluminum bronze (copper, aluminum, and iron) and marine-grade stainless steel (mostly iron, chromium, and nickel).
Both are technically known as paramagnetic, or “nonmagnetic” in layman’s terms. That is, they don’t stick to a magnet. Yet when they are mixed in equal proportions, the resulting alloy turns out to be a “soft” ferromagnet. That is, it is attracted to “hard” ferromagnets — like the one on the fridge — but does not itself become one.
“We used these two paramagnetic materials to create a gradient alloy with an InssTek MX-1000 3D printer. It employs a technique called directed energy deposition, which involves depositing powdered material from a nozzle and simultaneously melting it with a laser. The resulting alloy exhibited ferromagnetic properties to an extent that depended on the ratio between the two constituent materials,” says researcher Oleg Dubinin.
“Our study also provides a theoretical explanation of the emergence of ferromagnetic properties in the alloy in terms of its atomic structure,” adds Dubinin, “while the two initial materials have a so-called face-centered cubic crystal structure, their combination results in a body-centered cubic structure.”
In the former, metal atoms sit in the corners of imaginary cubes and on their faces. In the latter, there are metal atoms at the centers of the invisible cubes instead of on their faces. This second arrangement gives the material its ferromagnetic properties.