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Autor

  • Mishurova, Tatiana (48)
  • Bruno, Giovanni (38)
  • Cabeza, Sandra (12)
  • Kromm, Arne (12)
  • Thiede, Tobias (12)
  • Requena, G. (10)
  • Nadammal, Naresh (9)
  • Sevostianov, I. (9)
  • Evsevleev, Sergei (8)
  • Cabeza, S. (6)
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Erscheinungsjahr

  • 2021 (1)
  • 2020 (13)
  • 2019 (4)
  • 2018 (15)
  • 2017 (10)
  • 2016 (5)

Dokumenttyp

  • Zeitschriftenartikel (28)
  • Beitrag zu einem Tagungsband (7)
  • Posterpräsentation (7)
  • Vortrag (6)

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  • Englisch (45)
  • Deutsch (3)

Referierte Publikation

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Schlagworte

  • Additive manufacturing (23)
  • Residual stress (22)
  • Computed tomography (13)
  • Selective laser melting (10)
  • Synchrotron X-ray diffraction (9)
  • Neutron diffraction (8)
  • Ti-6Al-4V (8)
  • IN718 (4)
  • Metal matrix composite (4)
  • Additive Manufacturing (3)
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Organisationseinheit der BAM

  • 8 Zerstörungsfreie Prüfung (48)
  • 8.5 Mikro-ZfP (47)
  • 5 Werkstofftechnik (13)
  • 9 Komponentensicherheit (13)
  • 9.4 Integrität von Schweißverbindungen (13)
  • 5.0 Abteilungsleitung und andere (9)
  • 9.2 Versuchsanlagen und Prüftechnik (4)
  • 7 Bauwerkssicherheit (3)
  • 7.1 Baustoffe (3)
  • 5.1 Materialographie, Fraktographie und Alterung technischer Werkstoffe (2)
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Determination of macroscopic stress from diffraction experiments: A critical discussion (2020)
Mishurova, Tatiana ; Bruno, Giovanni ; Evsevleev, Sergei ; Sevostianov, I.
The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and Show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kröner’s model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool.
Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V (2020)
Mishurova, Tatiana ; Artzt, K. ; Haubrich, J. ; Evsevleev, Sergei ; Evans, Alexander ; Meixner, M. ; Serrano Munoz, Itziar ; Sevostianov, I. ; Requena, G. ; Bruno, Giovanni
The laser powder bed fusion (LPBF) production process often results in large residual stress (RS) in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro-RS (i.e., stress at the component level) by means of diffraction-based techniques is still a great challenge, because the link between diffraction-based strain and macro-RS is not trivial. In this study, we experimentally determine (by means of in-situ synchrotron radiation diffraction) this link for LPBF Ti-6Al-4V. We compare our results with commonly used models to determine the so-called diffraction elastic constants (DECs). We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account (as is the case of additively manufactured materials), a radically new approach is desirable.
Explaining Deviatoric Residual Stresses in Aluminum Matrix Composites with Complex Microstructure (2020)
Evsevleev, Sergei ; Sevostianov, I. ; Mishurova, Tatiana ; Hofmann, M. ; Garcés, G. ; Bruno, Giovanni
The residual stresses in multiphase metal Matrix composites with both random planar-oriented short fibers and particles were studied by neutron diffraction and by a model based on the reformulation of classic Maxwell’s homogenization method. Contrary to common understanding and state-of-the-art models, we experimentally observed that randomly oriented phases possess non-hydrostatic residual stress. The recently developed modeling Approach allows calculating the residual stress in all phases of the composites. It rationalizes the presence of deviatoric stresses Accounting for the interaction of random oriented phases with fibers having preferential orientation.
Residual stress in selective laser melted Inconel 718: Influence of the removal from base plate and deposition hatch length (2018)
Thiede, Tobias ; Cabeza, S. ; Mishurova, Tatiana ; Nadammal, N. ; Kromm, Arne ; Bode, Johannes ; Haberland, C. ; Bruno, Giovanni
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.
Quality control in additive manufacturing via in-situ monitoring and non-destructive testing (2018)
Maierhofer, Christiane ; Thiel, Erik ; Altenburg, Simon J. ; Mohr, Gunther ; Thiede, Tobias ; Mishurova, Tatiana ; Paul, Andrea ; Kranzmann, Axel ; Hilgenberg, Kai ; Pittner, Andreas ; Bruno, Giovanni ; Sommer, Konstantin ; Gumenyuk, Andrey
More than 80 representatives of SMEs, industrial companies and research institutes met on September 12 at the workshop "Challenges in Additive Manufacturing: Innovative Materials and Quality Control" at BAM in Adlershof to discuss the latest developments in materials and quality control in additive manufacturing. In special lectures, researchers, users and equipment manufacturers reported on the latest and future developments in additive manufacturing. Furthermore, funding opportunities for projects between SMEs and research institutions on a national and European level were presented.
Influence of deposition hatch length on residual stress in selective laser melted Inconel 718 (2018)
Bruno, Giovanni ; Thiede, Tobias ; Mishurova, Tatiana ; Kromm, Arne ; Nadammal, Naresh ; Bode, Johannes ; Cabeza, Sandra
The present study aims to evaluate the bulk residual stresses in SLM parts by using neutron diffraction measurements performed at E3 line -BER II neutron reactor- of Helmholtz-Zentrum für Materialien und Energie (HZB) Berlin. Together with microstructure characterization and distortion measurements, it is possible to describe the stress state throughout the whole sample. The sample was measured in as-build condition (on a build plate) and after releasing from the build plate. The used material is the nickel based superalloy 718. This alloy is widely used in aerospace and chemical industries due to its superior corrosion and heat resistant properties. Obtained results indicated different residual stress states for each of the transversal, longitudinal and normal component. The normal and transversal component exhibits a rather compressive behavior while the longitudinal was tensile in the center part of the sample and became compressive towards the tip. As expected, the absolute values of all stress components decreased after releasing the sample from the building plate. A surface scan utilizing a coordinate-measuring machine (CMM) allowed us to present top surface distortion before and after releasing. The top surface showed a distortion around ±80µm after releasing. Microstructure evolution in the scanning-building cross-section is largely dominated by columnar grains. In addition, many small random orientated grains are prominent in the regions of a laser overlap during SLM. In summary, for the sample of superalloy 718 manufactured by SLM, a small distortion occurred when removing the sample from the build plate whereby the residual stress state decreases. Moreover, the observed columnar grains in the building direction could give a reason for the lowest stress values in that normal direction. However, the most important parameter controlling the residual stresses is the temperature gradient. Hence, future investigations are planned for a different scan strategy to distribute the laser impact in a more homogenous manner.
Effect of hatch length on the development of microstructure, texture and residual stresses in selective laser melted superalloy Inconel 718 (2017)
Nadammal, Naresh ; Cabeza, Sandra ; Mishurova, Tatiana ; Thiede, Tobias ; Kromm, Arne ; Seyfert, Christoph ; Farahbod, Lena ; Haberland, Christoph ; Schneider, Judith Ann ; Portella, Pedro Dolabella ; Bruno, Giovanni
In the present study, samples fabricated by varying the deposition hatch length during selective laser melting of nickel based superalloy Inconel 718 were investigated. Microstructure and texture of these samples was characterized using scanning electron microscopy, combined with electron back-scattered diffraction, and residual stress assessment, using neutron diffraction method. Textured columnar grains oriented along the sample building direction were observed in the shorter hatch length processed sample. A ten-fold increase in the hatch length reduced the texture intensity by a factor of two attributed to the formation of finer grains in the longer hatch length sample. Larger gradients of transverse residual stress in the longer hatch length sample were also observed. Along the build direction, compressive stresses in the shorter hatch length and negligible stresses for the longer hatch length specimen were observed. Changes to the temperature gradient (G) in response to the hatch length variation, influenced the G to growth rate (R) ratio and the product G × R, in agreement with the microstructures and textures formed. For the residual stress development, geometry of the part also played an important role. In summary, tailored isotropy could be induced in Inconel 718 by a careful selection of parameters during selective laser melting.
Der Einfluss der Hatch-Länge und der Probenabtrennung von der Bauplatte auf den Eigenspannungszustand in SLM-Bauteilen aus IN718 (2017)
Thiede, Tobias ; Mishurova, Tatiana ; Cabeza, S. ; Nadammal, Naresh ; Bode, Johannes ; Kromm, Arne ; Haberland, C. ; Bruno, Giovanni
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.
The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts (2017)
Mishurova, Tatiana ; Thiede, Tobias ; Cabeza, Sandra ; Bruno, Giovanni ; Kromm, Arne ; Nadammal, Naresh
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 the cutting 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 of 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.
Pandora’s Box–Influence of Contour Parameters on Roughness and Subsurface Residual Stresses in Laser Powder Bed Fusion of Ti-6Al-4V (2020)
Artzt, K. ; Mishurova, Tatiana ; Bauer, P.-P. ; Gussone, J. ; Barriobero-Vila, P. ; Evsevleev, Sergei ; Bruno, Giovanni ; Requena, G. ; Haubrich, J.
The contour scan strategies in laser powder bed fusion (LPBF) of Ti-6Al-4V were studied at the coupon level. These scan strategies determined the surface qualities and subsurface residual stresses. The correlations to these properties were identified for an optimization of the LPBF processing. The surface roughness and the residual stresses in build direction were linked: combining high laser power and high scan velocities with at least two contour lines substantially reduced the surface roughness, expressed by the arithmetic mean height, from values as high as 30 μm to 13 μm, while the residual stresses rose from ~340 to about 800 MPa. At this stress level, manufactured rocket fuel injector components evidenced macroscopic cracking. A scan strategy completing the contour region at 100 W and 1050 mm/s is recommended as a compromise between residual stresses (625 MPa) and surface quality (14.2 μm). The LPBF builds were monitored with an in-line twin-photodiode-based melt pool monitoring (MPM) system, which revealed a correlation between the intensity quotient I2/I1, the surface roughness, and the residual stresses. Thus, this MPM system can provide a predictive estimate of the surface quality of the samples and resulting residual stresses in the material generated during LPBF.
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