June 2021 ESRFnews16

ADDITIVE MANUFACTURING

materials scientist Guillermo Requena at the German Aerospace Centre in Cologne, some of the earlier hype in the field is beginning to seem justified. We know the restrictions, and the advantages and disadvantages, he explains. We re in a situation now where the technology can really be put into practice.

Although its roots go back to the 1980s, additive manufacturing really started in the early 1990s, when researchers working independently at the Massachusetts Institute of Technology in the US and the Fraunhofer Society in Germany developed the first widely applic- able processes. Today there are more than half a dozen different versions. One of the most popular is laser powder-bed fusion (LPBF), in which a machine deposits a layer of metallic or plastic powder before selectively melting and fusing it with a laser, raster fashion; once a layer is complete, a new bed of powder is laid down and selectively fused until a 3D object is finished. Similar to this is electron-beam powder-bed fusion, in which an electron beam performs the melting and fusing. A third popular version is known as directed energy deposition, in which the raw material is already molten when it is deposited on a bed, where it cools and solidifies. Usually, any of these versions of additive manufacturing

in engineering has to be part of a longer processing chain that includes post-processing steps and quality control. Post-processing has been a major hurdle in the way of wider uptake. Components made by additive manufacturing rarely emerge in their final form; for instance, their sur- faces are often poor in quality and must undergo long and expensive heat treatments to improve fatigue resistance. According to Requena, one reason is the raw materials used typically the same ones used for other types of process- ing, such as casting or forging. We always knew that these could be improved, he says. Every method of manufac- turing suits a particular type of material. Having invented a new manufacturing technology, we need to optimise the existing materials, or invent new ones.

Bespoke materials Last year, together with colleagues from various institutions in Germany, Spain, Hungary and France, Requena developed one potential new material: an ultra- fine eutectic titanium-iron alloy. Eutectic alloys consist of at least two phases of metals, which, when mixed, have lower melting temperatures than they do individually, and are already used for many engineering applications, such as the pistons of combustion engines. Scientists already knew that, when cooled rapidly, some eutectic alloys solidify with ultra-fine microstructures and can become very strong while retaining their ductility. However, conventional rapid solidification techniques are usually only able to produce droplet-sized samples. Using LPBF, Requena and colleagues found that they could produce arbitrarily large samples of their ultra-fine eutectic titanium-iron alloy; in partnership with the engineering company G+L Innotec in Laupheim,

Figure 1: Additive manufacturing is best suited to the production of high-performance, intricate parts that would normally need to be made from several components. Printed by ESRF user Guillermo Requena and colleagues, this turbocharger compressor (left) makes use of an unusually strong eutectic titanium-iron alloy. (Right) Synchrotron tomography at the ID16A beamline exposes the alloy s ultra-fine microstructures.

G U IL LE

R M O R E Q U E N A / A P P L. M AT ER

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The EBS energy and flux will really benefit us, for both increased speed and the palette of alloys we can study

G U IL LE

R M O R E Q U E N A / A P P L. M AT ER

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