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The additive manufacturing technology became in recent years one of the most widely investigated research fields in materials science due to its promising results aiming at reducing the amount of used material and also to increase the precision in complex geometry of metallic components. Laser powder bed fusion (LPBF) is one of the most commonly used metal 3D printing process in which a laser selectively melts or partially melts a bed of powdered material. The fast cooling rates are the origin of large stress gradients, which can strongly influence the performance during service life. These residual stresses and stress concentrations in the parts are usually relieved by thermal treatments after the build and before the components are removed from the build plates. Therefore, the estimation of the quantity and distribution of residual stresses becomes a key for optimizing the viability of production parameters.
A white high-energy X-ray beam in transmission mode is a suitable tool to explore nondestructively depth-resolved residual stresses in the bulk of materials. A monochromatic high-energy X-ray beam in combination with a conical slit cell (CSC) [1] also enables the determination of the strain components over the whole sample thickness with sufficient spatial resolution. With the aim of strengthening the industrial access to these non-destructive synchrotron technologies, the EU project EASI-STRESS will enable a better understanding of the formation and progression of residual stresses by direct comparison with accepted destructive techniques.
The characterization of residual stresses in an AM austenitic steel 316L part in as-built and heat-treated conditions by means of high-energy synchrotron X-rays with a) a monochromatic beam with CSC, and b) a white beam in transmission and reflection mode will be presented.
References
[1] P. Staron, T. Fischer, J. Keckes, S. Schratter, T. Hatzenbichler, N. Schell, M. Müller, A. Schreyer, Depth-Resolved Residual Stress Analysis with High-Energy Synchrotron X-Rays Using a Conical Slit Cell, Mater. Sci. Forum 768-769 (2014) 72-75