Additive manufacturing The fourth dimension in 3D printing opens up unprecedented material properties

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Compared to established manufacturing methods, the technology of 3D printing is still a relatively young technology. The newly established department of "Materials for Additive Manufacturing" at TU Berlin demonstrates that products with complex material compositions and entirely novel properties, previously unachievable, can be produced using 3D printing. And this might be what the fourth dimension in 3D printing looks like:

Molten hot steel flows into a billet form and, after solidifying, is still glowing as it is rolled into sheets or bars. These can then be deep drawn, bent, or forged into various shapes. "With each of these transformations, the material structure changes as well, but the most important material properties are already determined during the casting of the raw material," says Prof. Dr.-Ing. Christian Haase, who heads the new department of "Materials for Additive Manufacturing" at TU Berlin. Unlike this top-down approach, additive manufacturing uses a bottom-up method: In 3D printing, the final product is created in one step, except for subsequent work such as polishing. In the so-called powder bed process, a laser or electron beam selectively melts a powdered material at specific points, allowing a complex part to be built layer by layer with almost arbitrary shapes. In "laser cladding," even very different materials can be combined to build a workpiece, with the desired material being sprayed on just before melting by the laser, for example as a powder-gas mixture. Even though 3D printing is still a relatively young technology compared to established manufacturing methods, it can produce products with complex material compositions and entirely novel properties that were previously unachievable. This is the focus of the newly established department of "Materials for Additive Manufacturing" led by Prof. Dr.-Ing. Christian Haase. His chair is the second TU professorship in cooperation with the industry and science campus Werner-von-Siemens Centre for Industry and Science e.V. (WvSC).

Bottom-up approach in 3D printing

"Through this production method, it is possible to set different material and surface properties at various points of the workpiece during the shaping process, on completely different size scales," says Christian Haase. In addition to the possibility of combining different materials in laser cladding, the energy, beam diameter, and movement speed of the laser are also parameters that can influence material properties. "From the different chemical compositions and the arrangement of individual atoms to larger, desired deviations in the crystal structure to the grain structure of the material, which is sometimes visible to the naked eye—we can make targeted changes in all these size ranges."

A multitude of possible combinations for the optimum

The ability to integrate entirely new material properties into the microstructure of materials in additive manufacturing, alongside the virtually free choice of three-dimensional shapes, is also referred to as the fourth dimension in 3D printing by professionals. Over the next five years, Christian Haase will explore this additional dimension with the ERC Starting Grant "HeteroGenius4D." "The challenge here is that the number of parameters that can be changed is very high. Just the space of chemical compositions one can work with is extremely broad, even when limited to metallic materials," explains Haase. Additionally, there are process parameters like the properties and the control of the laser beam. "Thus, there are a multitude of possible combinations from which the optimum must be filtered out."

Combination of high-throughput experiments and material simulations

To tackle this challenge, Christian Haase relies on computer simulations of new materials that can predict their properties. "However, this only works if these simulations are based on a solid data foundation," says Haase. Therefore, he and his team also conduct so-called high-throughput experiments, where test specimens are created at high speed using laser cladding, and automated measurements of the hardness of these specimens and electron microscopic images of them are carried out. "In the end, we have entire maps that show how the material properties depend on the chemical composition and, for example, the laser power. These maps then allow simulation programs to perform a refined search for the exact material properties desired for a specific application."

Additive manufacturing playing a helpful role in the energy transition

3D printing is traditionally used in industries where complex parts are needed in small quantities. This includes applications like molds and special tools in production facilities, the semiconductor industry, and also in aerospace. "Additive manufacturing will also play a helpful role in the energy transition," says Christian Haase, citing a research project he conducted in the mobility sector. It focused on high-strength aluminum alloys where the expensive and geopolitically critical element scandium was to be replaced. Using his approach of experimentation and simulation, Haase's group was able to identify the cheaper element zirconium as a substitute, which showed better properties in the alloy and also saved weight. "In the hot sections of gas turbines, whether in airplanes or in the conversion of natural gas or hydrogen into electricity, 3D printing can bring great advantages, for example because new geometries make entirely different, integrated cooling systems in the turbine possible," says Haase, who also has significant project experience in this area.