June 2021 ESRFnews 17

Germany, they produced a functional compressor for an automotive turbocharger. More impressively, at the ID16A beamline, they were able to show via near-field synchro- tron ptychographic X-ray computed tomography, at a reso- lution down to 39 nm, that the microstructures were even finer and the bulk even stronger than those previously obtained (Appl. Mater. Today 20 100767). ID16A gave us new insights into the interior of our material, Requena says (see fig. 1). Another long-term ESRF user who studies additive

manufacturing is Peter Lee of University College Lon- don in the UK. For the ID19 beamline, Lee and his col- leagues have created a bespoke LPBF machine with a large aperture to allow high-flux, pink X-ray beams to pass through, so that they could study the ultra-fast, repeating melt solidification process in situ. Last year they operated the machine in keyhole mode, a desirable mode of LPBF where the laser penetrates deeply and efficiently into the powder bed; unfortunately this mode may create pores that weaken the material in the process. The ID19 data revealed how these pores are formed in a titanium alloy at microsecond intervals, and suggested that they could be avoided with a shaped laser beam, which Lee s team is now developing (Appl. Mater. Today 20 100650).

Multiple techniques The unique draw of the ESRF s ID19 beamline com- pared with beamlines at other high-energy synchrotrons, explains Lee, is the ability to employ high flux at high energies, opening up the study of metals with higher atomic numbers, such as nickel super-alloys. With the arrival of the EBS, he adds, the higher energy and higher flux will really benefit us, for both increased speed and the palette of alloys we can study . Several ESRF beamlines see users regularly come to

study other aspects of additive manufacturing. In 2019 Jules Harings of Maastricht University in the Netherlands and colleagues used ID15A, specifically its wide-angle X-ray diffraction tomography, to study the manufacture of thermoplastic objects by fused deposition modelling, a variant of direct energy deposition in which polymers are melted before being extruded and deposited. Previously,

plastics manufactured by this technique lacked their usual level of mechanical performance, because the poly- mers in adjacent layers did not mix with one another. To overcome this, Harings and colleagues tried depositing left- and right-handed polymers alternately. The ID15A data showed that when these two mirrored polymers meet, they are encouraged to permanently intertwine because their mixed form (their stereocomplex ) is more stable thermodynamically (ACS Appl. Polym. Mater. 1 2131). Meanwhile, at the ESRF s ID22 beamline, Maurizio

Vedani of the Polytechnic University of Milan in Italy and colleagues have used synchrotron X-ray diffraction (XRD) to study a promising new alloy for LPBF. Beginning with a standard alloy for traditional manufacturing, based on aluminium, zinc, magnesium and copper, the researchers added silicon to try to reduce the alloy s propensity to crack after solidification in LPBF, while still hot. The diffraction data allowed the researchers to precisely detect secondary phases within the material that would have been invisible to non-synchrotron XRD, giving them confidence about its suitability (J. Alloys Compd. 801 243). The alloy is now basically ready for use, says Vedani. More and more specialised components are being

manufactured additively. Requena s group is in the pro- cess of building a combustion chamber for a rocket engine. And in a collaboration with the University of Sheffield in the UK, Lee s group manufactured light, aerodynamic handlebars for the British cyclist Bradley Wiggins, helping him to break the world hour track record in 2015. In the future, says Lee, X-ray data will be able to provide a ground truth to validate characterisation with optical and infra- red instruments, further reducing the development cost. In the opposite direction, the ESRF is participating in a European project to provide companies with a simple ser- vice to generate stress maps from synchrotron strain data (see Easy does it , above). Much like the process itself, advancements in additive

manufacturing have been proceeding step-wise. Perhaps only now are scientists beginning to see the full possibil- ities emerge. 

Jon Cartwright

In a range of sectors, such as energy, automotive and aerospace, industry has to be certain that metallic components will not fail due to stress fatigue. Often there is over-caution simply because the levels of stress in the components are not accurately known. This is particularly important in additive manufacturing, where the fast melt and solidification cycles in non-equilibrium regimes result in complex phase transformations, potentially leading to additional stresses between layers.

A new European project, EASI-STRESS, aims to help this situation by improving access to non-destructive diffraction

techniques at neutron and synchrotron facilities, such as the ESRF. Synchrotron X-ray diffraction studies can already probe the strain within samples at great depth, and convert that strain into 3D stress maps after data reduction, modelling and analysis. But according to Ennio Capria, the ESRF deputy head of business development, there is a unique opportunity to make the process more streamlined, in particular through standardisation and the construction of a dedicated platform. The consortium of 14 partners will tackle the whole process, from assessment to strain-data acquisition to stress-map extraction. In this way, says

Capria, industrial clients will obtain reliable answers swiftly and with no fuss. With EASI-STRESS, we re moving from offering an experiment to offering a service.

Meanwhile, the ESRF and the Institut Laue- Langevin on the EPN campus are working with the Manufacturing Technology Centre, a research institute in Coventry, UK, to define an International Organization for Standardization (ISO) standard for neutron and X-ray tomography in additive manufacturing. The standard is expected to give industrial clients an appropriate framework to fully benefit from the advantages offered by tomographic images recorded at the ESRF.

EASY DOES IT ADDITIVE MANUFACTURING