Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V
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TION
ONE of the most important issues in laser powder bed fusion (LPBF) additive manufacturing (AM) is the influence of residual stress (RS) on parts during production and service.[1] High-temperature gradients and cooling rates during production often lead to tensile RS.[2–4] Such stresses may reach values close to the yield
TATIANA MISHUROVA, SERGEI EVSEVLEEV, ALEXANDER EVANS, and ITZIAR SERRANO MUNOZ are with the Bundesanstalt fu¨r Materialforschung und -pru¨fung (BAM), Unter den Eichen 87, Berlin 12205, Germany. Contact email: [email protected] KATIA ARTZT and JAN HAUBRICH are with the Institute of Materials Research, German Aerospace Center (DLR; Deutsches Zentrum fu¨r Luft -und Raumfahrt), Linder Ho¨he, Cologne 51147, Germany. MATTHIAS MEIXNER is with the Helmholtz-Zentrum Berlin fu¨r Materialien und Energie GmbH, HahnMeitner Platz 1, 14109, Berlin, Germany. IGOR SEVOSTIANOV is with the Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, NM 88003-8001. GUILLERMO REQUENA is with the Institute of Materials Research, German Aerospace Center (DLR; Deutsches Zentrum fu¨r Luft -und Raumfahrt), Linder Ho¨he, and the Metallic Structures and Materials Systems for Aerospace Engineering, RWTH Aachen University, 52062 Aachen, Germany. GIOVANNI BRUNO is with the Bundesanstalt fu¨r Materialforschung und -pru¨fung (BAM), Unter den Eichen 87, and the Institute of Physics and Astronomy, University of Potsdam, KarlLiebknecht-Straße 24/25, Potsdam 14476, Germany. Manuscript submitted September 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
limit in the subsurface region,[5,6] thereby decreasing the performance of the material, especially during cyclic loading. Moreover, RS can induce severe geometrical distortions and cracking,[4] thus nullifying the main advantage of freeform fabrication. Therefore, quantification of RS and validation of thermomechanical models by experimental results are among the greatest challenges for qualification of AM parts. The nondestructive (diffraction-based) experimental determination of RS is directly connected to the microstructure of the part. The complicated thermal history and high anisotropy of LPBF parts lead to microstructures and mechanical properties different from conventionally manufactured materials (wrought or cast).[7] The microstructure in LPBF materials is additionally highly dependent on process parameters.[8–10] Therefore, the elastic properties may differ from conventional materials and even vary with the production parameters of LPBF. The knowledge about elastic properties is important for RS analysis by diffraction techniques, where the so-called diffraction elastic constants (DECs) are used[11] to connect the measured microstrain (diffraction based, i.e., averaged over grains of a particular family) with the macrostress (at the component length scale). Therefore, the use of incorrect DECs can lead to erroneous RS values[12] and misestimation of the material performance.
In-situ synchrotron X-ray diffraction (SXRD) or neutron diff
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