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- IN718 (8) (entfernen)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (5)
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- 5 Werkstofftechnik (4)
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- 9.6 Additive Fertigung metallischer Komponenten (1)
Eingeladener Vortrag
- nein (2)
The elastic properties (Young's modulus, shear modulus) of Ni-based alloy Inconel IN718 were investigated between room temperature and 800 °C in an additively manufactured variant (laser powder bed fusion, PBF‑LB/M) and from a conventional process route (hot rolled bar). The moduli were determined using the dynamic resonance method. The data set includes information on processing parameters, heat treatments, grain size, specimen dimensions and weight, Young’s and shear modulus as well as their measurement uncertainty.
The dataset was generated in an accredited testing lab using calibrated measuring equipment. The calibrations meet the requirements of the test procedure and are metrologically traceable. The dataset was audited as BAM reference data.
For metal-based additive manufacturing (AM) to achieve leaner designs and enable longer life predictions, it is imperative to gain a detailed knowledge of the residual stress (RS) built-up. Laser powder bed fusion (LPBF) is an AM technique particularly prone to RS because of the highly localized heat source, extremely high cooling rates (in the order of 103-107 K/s), and successive cooling and heating cycles of the solidified material. Furthermore, RS analysis of LPBF materials by diffraction methods is peculiar because of the complexity of the thermal history, the possibility of encountering high levels of surface roughness, spatial textural variations and/or changes in solute concentrations at the component scale.
Diverse aspects of the influence of scanning strategies on the as-built residual stress state of a LPBF IN718 alloy will be presented, with particular focus on the challenges that AM microstructures pose for a reliable RS determination.
Influence of the scanning strategy on the residual stress state in IN718 additive manufactured parts
(2020)
Laser Powder Bed Fusion (L-PBF) is an additive manufacturing technique enabling the design of complex geometries that are unrivalled by conventional production technologies. Nevertheless, L-PBF process is known to induce a high amount of residual stresses (RS) due to the high temperature gradients present during powder melting by laser. High tensile residual stresses are to be found the edges whereas the bulk material shows balancing compressive RS. Literature shows that the RS is highly sensitive to the process parameters. In particular, this study presents the characterization of the RS state in two L-PBF parts produced with a rastering scan vector that undergoes 90° or 67° rotation between subsequent layers.
The residual stress distribution in IN718 elongated prisms produced by Selective Laser Melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction.
Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed (RE) from the base plate were characterized.
While surface stress fields seem constant for AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements.
Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e. with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the baseplate.
Additive Manufacturing (AM) of metals has become industrially viable for a large variety of applications, including aerospace, automotive and medicine. Powder bed techniques such as Selective Laser Melting (SLM) based on layer-by-layer deposition and laser melt enable numerous degrees of freedom for the geometrical design. Developing during the manufacturing process, residual stresses may limit the application of SLM parts by reducing the load bearing capacity as well as induce unwanted distortion depending on the boundary conditions specified in manufacturing.
The residual stress distribution in the bulk of IN718 elongated prisms produced by SLM was studied non-destructively by means of neutron diffraction. The samples with different scanning strategies, i.e. hatching length, were measured in as-build condition (on a build plate) and after removal from the build plate.
The absolute values of all stress components decreased after removal from the build plate. Together with surface scan utilizing a coordinate-measuring machine (CMM), it is possible to link the stress release to the sample distortion. Obtained results indicated different residual stress states for each of the transversal, longitudinal and normal component depending on the thermal gradient in the respective direction.
The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts
(2018)
The effect of support structure and of removal from the base plate on the residual stress state in selective laser melted IN718 parts was studied by means of synchrotron X-ray diffraction. The residual stresses in subsurface region of two elongated prisms in as-built condition and after removal from the base plate were determined. One sample was directly built on a base plate and another one on a support structure. Also, the distortion on the top surface due to stress release was measured by contact profilometry. High tensile residual stress values were found, with pronounced stress gradient along the hatching direction. In the sample on support, stress redistribution took place after removal from the base plate, as opposed to simple stress relaxation for the sample without support. The sample on support structure showed larger distortion compared to sample without support. We conclude that the use of a support decreases stress values but stress-relieving heat treatments are still needed.
Die Schicht-für-Schicht additive Fertigung (AM) in Form des selektiven Laserschmelzens (SLM) bietet einerseits Vorteile bezüglich des Probendesigns, andererseits sind thermische Eigenspannungen (ES) aufgrund des hohen Temperaturgradienten unvermeidbar. Diese Eigenspannungen wurden in zwei SLM-gefertigten Proben aus IN718 zerstörungsfrei mit Neutronenstreuung hinsichtlich der folgenden zwei Einflüsse analysiert: der Einfluss der Hatch-Länge und das Abtrennen des Werkstücks von der Bauplatte. Begleitet wurden die Messungen der Eigenspannungen durch optische Mikroskopie und die taktile Vermessung der Oberfläche. Eine Korrelation zwischen den Eigenspannungen und der Hatch-Länge konnte beobachtet und erklärt werden.
Der Einfluss der Probenabtrennung von der Bauplatte auf den Eigenspannungszustand in SLM IN718
(2017)
Die Schicht-für-Schicht additive Fertigung (AM) in Form des selektiven Laserschmelzens (SLM) bietet einerseits Vorteile bezüglich des Probendesigns, andererseits sind thermische Eigenspannungen (ES) aufgrund des hohen Temperaturgradienten unvermeidbar. Diese Eigenspannungen wurden in zwei SLM-gefertigten Proben aus IN718 zerstörungsfrei mit Neutronenstreuung hinsichtlich der folgenden zwei Einflüsse analysiert: der Einfluss der Hatch-Länge und das Abtrennen des Werkstücks von der Bauplatte. Begleitet wurden die Messungen der Eigenspannungen durch optische Mikroskopie und die taktile Vermessung der Oberfläche. Eine Korrelation zwischen den Eigenspannungen und der Hatch-Länge konnte beobachtet und erklärt werden.