The Skolkovo Institute of Science and Technology (Skoltech), a private technical institute located in Moscow, Russia, established an additive manufacturing (AM) laboratory back in 2017. Since then, it has been researching a range of 3D printing techniques, and more recently found a way to “turn” a non-magnetic alloy to a magnetic material through a directed energy deposition (DED) process.
They achieved this by using the 3D printer to fuse two materials in an alloy with a composition that continuously changes from one region of the sample to the other, endowing the alloy with gradient magnetic properties.
Despite the nonmagnetic nature of the constituent materials, the alloy exhibits magnetic properties, Skoltech said.
“3D printing has grown into a full-blown industrial technology used to produce airplane parts, patient-matched implants and prosthetics, jewelry, and custom-fit shoes, among other things,” said research scientist Dr Stanislav Evlashin, who led the project, about the process. “The main advantage of 3D printing is the ability to produce objects with very complex shapes that are impossible or too expensive to make with conventional manufacturing techniques, such as casting, rolling, and stamping. The technology also enables faster and riskier prototyping, and greater flexibility in terms of product customization and how many items are produced. And then there’s the added benefit of reduced waste.”
However, one of the limitations of 3D printing is that it tends to use one homogeneous material or mixture throughout the entire part produced. However, “by varying the composition from one part of the item to another, it could be endowed with properties that continuously change,” Dr Evlashin said.
One example of this would be a rod made of an alloy of two metals with a ratio that 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.
In October 2021 Skoltech researchers reported on an experiment that produced such an alloy. Its two components — the metals A and B above — are themselves alloys: aluminum bronze (made of copper, aluminum, and iron) and marine-grade stainless steel (made of mostly iron, chromium, and nickel).
Both are paramagnetic, a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. This means that they don’t stick to a magnet. However, when they are mixed in equal proportions, the resulting alloy turns out to be a “soft” ferromagnet. Ferromagnetic materials can be divided into magnetically "soft" materials, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. This alloy in this case is attracted to “hard” ferromagnets – such as fridge magnets – but does not itself become one.
Skoltech scientists used these two paramagnetic materials to create a gradient alloy using an InssTek MX-1000 3D printer, manufactured by Korean company InssTek, established in 2001.
The printer uses DED, which, like other AM processes, 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,” said Oleg Dubinin, lead author of the report published in The Journal of Materials Processing Technology. (Besides the researchers from Skoltech, the study also features scientists from St. Petersburg State Marine Technical University, National Research Center Kurchatov Institute, and Belgorod State University.)
“Our study also provides a theoretical explanation of the emergence of ferromagnetic properties in the alloy in terms of its atomic structure,” he said. “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.
“Gradient soft magnetic alloys could find applications in machine engineering, for example, in electrical motors,” commented Dr Evlashin, a leading research scientist at Skoltech. “Our findings show that directed energy deposition is not just a way to 3D-print gradient materials, but also a way to discover new alloys. Besides that, the technology is highly efficient and suitable for manufacturing even large-size parts quickly.”
Metal Powder Report carried out a deep dive with Dr Evlashin about the 3D printing process and the research.
Will using two metals in one 3D part become more common?
Definitely yes. Conventional production methods, such as casting, are not very well suitable for multi-material production, and most production processes have been developed for single material parts or assemblies with different materials. But the ability to combine multiple alloys in one production process and in one produced part opens wide possibilities for the optimization of different physical properties. Joining ferromagnetic/paramagnetic metals together in one model – or metals with high heat resistance and high thermal conductivity, or soft and hard metals – shows us the way to create complex parts with properties not achievable before.
What are the challenges in 3D printing soft magnetic materials?
The magnetic properties of metals are very dependent on the metal’s microstructure. As a result, we need to precisely control printing parameters and environmental parameters during the production process to achieve the desired results. As well as this, any impurities, cracks, or chemical composition variations could lead to material properties degradation. This could be quite a challenge if you are developing a new magnetic alloy or adapting an existing one for additive technologies.
How could the 3D printing process be improved to make it easier to print more than one metal?
First of all, special software for multi-material model preparation could help a lot. Another important thing is precise material supply control. Sometimes two metal powders could have different particle sizes or different densities and it would be very useful to be able to control the percentage of each powder in a mixture in real-time.
What are the limits of this technology?
Most limitations are similar to those also found in regular welding. If two metals are weldable this means that you most likely can combine these metals in an additive process. Another limitation is the formation of a new phase that can embrittle the printed parts.
Besides electrical motors, what other applications could these parts be used for?
A combination of soft magnetic and paramagnetic alloys could be used in the production of magnetic encoders for different applications. Also, soft magnetic parts are suitable to make cores in electromagnets and DC transformers or in the production of relays. One of the advantages of AM is the ability to print cores with complex geometry for better magnetic flux control, cooling channels, areas with different magnetic properties, and so on. With regards to the Al-bronze alloy used in the research, these materials are used for the creation of self-friction surfaces where there is a need to decrease the friction coefficient. So, we can combine alloys with good mechanical properties with Al-bronze for the decrease the friction coefficient.
What do you think is the current state of 3D printing research, particularly in Russia and/or Eastern Europe?
Currently, the additive market in Russia is growing quite fast and so is 3D printing research. But this market is still far behind compared to Europe, Asia, or North America. This could be caused by a lack of local manufacturers of equipment and materials.
Do you think metal 3D printing is scaling up successfully?
Metal 3D printing applications are growing year by year. Not so long ago, AM was just a fast prototyping technology. We carried out metal powder sintering instead of elective laser melting SLM) and laser cladding for coating instead of DED 3d printing technology. But today, industrial giants like Siemens and GM have already adapted and improved existing additive technologies for the needs of their customers. This process is not lightning-fast – mostly because of the difference between conventional and additive technologies – but it happens slowly and steadily. Scientific research is speeding up the industrialization of additive technologies by imparting a better understanding of complex additive processes and giving industrial companies more confidence to take it to the next stage.