Neutrons detect hidden defects in 3D printed components
TECHNICAL UNIVERSITY OF MUNICHCorporate Communications Center
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Test procedures under scrutiny
Comparatively, neutrons detect most defects in 3D printed components
In the manufacture of turbines conventional processes often reach their limits. Therefore, additive manufacturing is increasingly used to produce complex, curved components with intricate structures. A research team from the Technical University of Munich (TUM) has now examined common methods used to locate defects inside components. In their investigation neutron grating interferometry, performed at the Heinz Maier-Leibnitz research neutron source (FRM II), achieved the best defect detection.
Laser beam melting is a common 3D printing process for turbine blades with internal cooling channels. During this process, a laser melts a thin layer of metal powder in predefined areas. Layer by layer, the component forms in a bed of powder. Similar to an archeological excavation, the component is then exposed and the remaining powder can be reused for the next printing process.
However, process instabilities can lead to defects and reduce the strength of the component. Typical defects are pores and cracks. Even partial or total separation of individual layers can occur.
Defects in safety-relevant components, such as turbine blades, can lead to serious consequences. "We therefore need to examine critical components after the manufacturing process and of course do so non-destructively," explains Cara Kolb from the Institute for Machine Tools and Industrial Management at TUM.
A look inside
For their experiments, the researchers produced test specimens with defects of different size and depth and then attempted their detection using non-destructive testing methods. This involved active infrared thermography (aIRT), ultrasonic testing (UT), X-ray computed tomography (CT) and neutron grating interferometry (nGI).
At the research neutron source doctoral student Tobias Neuwirth conducted the experiments at the ANTARES instrument. "We investigate components using neutron grating interferometry, observing the scattering and absorption of neutrons in a spatially resolved manner. Changes in these properties give us information about the type and size of the defects," he explains.
Greater penetration and better resolution with neutrons
Each of the methods tested has both potential and challenges. Neutron grating interferometry is complex and more expensive than the other test methods investigated, but of all the methods, it detected the most and the smallest defects.
"Neutrons can penetrate deep into the material and resolve the internal component structure with high resolution. They are particularly suited to nickel-based alloys, which are enormously important for the additive manufacturing of structural components in aerospace," concludes Cara Kolb.
Research into testing procedures that non-destructively assure the quality of 3D-printed components is very important: Such procedures reveal the likelihood of a component failure during operation. They are also ever more important as additive manufacturing in aircraft and cars, for example, increases.
C. G. Kolb, K. Zier, J.-C. Grager, A. Bachmann, T. Neuwirth, S. Schmid, M. Haag, M. Axtner, F. Bayerlein, C. U. Grosse, M. F. Zaeh
An investigation on the suitability of modern nondestructive testing methods for the inspection of specimens manufactured by laser powder bed fusion
SN Appl. Sci., 3, 713 (2021) – DOI: 10.1007/s42452-021-04685-3
High resolution images:
The experiments to investigate the ability of neutrons to detect defects were conducted at the FRM II using the ANTARES instrument of the Heinz Maier-Leibnitz Zentrum (MLZ). CT scans were provided by FIT AG, Lupburg.
Prof. Dr.-Ing. Michael Zäh
Technical University of Munich
Institute for Machine Tools and Industrial Management
Boltzmannstr. 15, 85748 Garching, Germany
Tel.: +49 89 289 15502 – E-mail: email@example.com
Technical University of Munich
Heinz Maier-Leibnitz Zentrum (MLZ)
James-Frank-Str. 1, 85748 Garching, Germany
Tel.: +49 89 289 11754 – E-mail: Tobias.Neuwirth@frm2.tum.de
The Technical University of Munich (TUM) is one of Europe’s leading research universities, with more than 600 professors, 48,000 students, and 11,000 academic and non-academic staff. Its focus areas are the engineering sciences, natural sciences, life sciences and medicine, combined with economic and social sciences. TUM acts as an entrepreneurial university that promotes talents and creates value for society. In that it profits from having strong partners in science and industry. It is represented worldwide with the TUM Asia campus in Singapore as well as offices in Beijing, Brussels, Mumbai, San Francisco, and São Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von Linde, and Rudolf Mößbauer have done research at TUM. In 2006, 2012, and 2019 it won recognition as a German "Excellence University." In international rankings, TUM regularly places among the best universities in Germany.