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Synchrotron-Based X-ray Microtomography Characterization of the Effect of Processing Variables on Porosity Formation in Laser Power-Bed Additive Manufacturing of Ti-6Al-4V

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Abstract

The porosity observed in additively manufactured (AM) parts is a potential concern for components intended to undergo high-cycle fatigue without post-processing to remove such defects. The morphology of pores can help identify their cause: irregularly shaped lack of fusion or key-holing pores can usually be linked to incorrect processing parameters, while spherical pores suggest trapped gas. Synchrotron-based x-ray microtomography was performed on laser powder-bed AM Ti-6Al-4V samples over a range of processing conditions to investigate the effects of processing parameters on porosity. The process mapping technique was used to control melt pool size. Tomography was also performed on the powder to measure porosity within the powder that may transfer to the parts. As observed previously in experiments with electron beam powder-bed fabrication, significant variations in porosity were found as a function of the processing parameters. A clear connection between processing parameters and resulting porosity formation mechanism was observed in that inadequate melt pool overlap resulted in lack-of-fusion pores whereas excess power density produced keyhole pores.

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Acknowledgements

The authors acknowledge the NextManufacturing Center at Carnegie Mellon University for supporting this work. They would also like to thank Dr. Xianghui Xiao and the rest of the 2-BM beamline staff at the Advanced Photon Source at Argonne National Laboratory for assisting in the acquisition of the synchrotron tomography data. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Finally the authors acknowledge the use of the Materials Characterization Facility at Carnegie Mellon University supported by Grant MCF-677785.

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Authors and Affiliations

  1. Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

    Ross Cunningham & A. D. Rollett

  2. Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

    Sneha P. Narra, Colt Montgomery & Jack Beuth

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  1. Ross Cunningham
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  2. Sneha P. Narra
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  3. Colt Montgomery
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  4. Jack Beuth
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  5. A. D. Rollett
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Correspondence to Ross Cunningham.

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Cunningham, R., Narra, S.P., Montgomery, C. et al. Synchrotron-Based X-ray Microtomography Characterization of the Effect of Processing Variables on Porosity Formation in Laser Power-Bed Additive Manufacturing of Ti-6Al-4V. JOM 69, 479–484 (2017). https://doi.org/10.1007/s11837-016-2234-1

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  • DOI: https://doi.org/10.1007/s11837-016-2234-1

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