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

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3D printing technology is considered a relatively young technology compared to traditional manufacturing methods. The fact that products with previously impossible, complex material compositions and thus entirely novel properties can be manufactured using 3D printing is proven by the newly established field of "Materials for Additive Manufacturing" at Technical University (TU) Berlin. And this is what the fourth dimension in 3D printing could look like:

Glowing hot steel flows into a bar shape and, after solidifying, still glowing, is rolled into sheets or rods. These can then be deep-drawn to different shapes, bent, or forged. "With each of these deformations, the material structure also changes, although 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 field of "Materials for Additive Manufacturing" at TU Berlin. In contrast to this top-down approach, additive manufacturing uses a bottom-up method: In 3D printing, the final product is produced 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 powder material at specific points, so that layer by layer, a complex component with almost arbitrary shapes can be created. In "laser cladding," even quite different materials can together build a workpiece, with the respective desired material being sprayed on shortly before melting by the laser as a powder-gas mixture. Although 3D printing is still a relatively young technology compared to established manufacturing methods, products with previously impossible, complex compositions and thus entirely new properties can be produced using 3D printing. This is where the newly established field of "Materials for Additive Manufacturing" by Prof. Dr.-Ing. Christian Haase comes in. 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, different material and surface properties can be set at different places on the workpiece during the shaping process, and this can be done on entirely different size scales," says Christian Haase. In addition to the ability to combine different materials in laser cladding, the energy, the beam diameter, and the movement speed of the laser are parameters that can influence material properties. "From the different chemical compositions and the arrangement of individual atoms, to more extensive, 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 variety of possible combinations for the optimum

This ability to integrate not only practically any freely chosen three-dimensional shape into additive manufacturing but also entirely new material properties into the microstructure of materials is also referred to as the fourth dimension in 3D printing in the professional world. Over the next five years, Christian Haase will investigate this additional dimension with the ERC Starting Grant "HeteroGenius4D." "The difficulty here is that the number of parameters that can be changed is very high. Even just the realm of chemical compositions one can work with is extremely broad, even if restricted to metallic materials," explains Haase. This includes process parameters such as the properties and control of the laser beam. "So, there are a multitude of possible combinations from which the optimum must be filtered out."

Combination of high-throughput experiments and material simulations

To solve this challenge, Christian Haase relies on computer simulations of new materials that predict their properties. "However, this only works if these simulations can be based on a solid database," says Haase. Therefore, he and his team also conduct so-called high-throughput experiments, where test samples are created at high speed using laser cladding, and automated measurements of the hardness of these samples and electron microscopic images of them are conducted. "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 can then be used by simulation programs to perform a refined search for the exact material properties desired for a specific application."

Additive manufacturing plays a helpful role in the energy transition

3D printing is traditionally used in the industry where complex components are needed in small quantities. For example, for molds and special tools in production facilities, in the semiconductor industry, but also in aerospace. "Additive manufacturing will also play a helpful role in the energy transition," says Christian Haase, citing as an example a research project he conducted in the mobility sector. It involved high-strength aluminum alloys where the expensive and geopolitically critical element scandium was to be replaced. With his approach combining experiment and simulation, Haase's group identified the more affordable element zirconium as a substitute, which showed better properties in the alloy and additionally saved weight. "Also in the hot areas of gas turbines, whether in an airplane 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 extensive project experience in this area.