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Lecture

Influence of porosity on the fatigue strength for additively manufactured Inconel 718

Wednesday (27.05.2020)
14:30 - 14:50

Nowadays, the development of additive manufacturing processes allows to manufacture metal parts of complex geometries integrating new functionalities and reducing the mass of components. However, the fatigue behavior of materials fabricated via additive manufacturing is currently not well understood. Particularly, this technique potentially leads to process induced defects such as pores due to the entrapment of argon gas in the powders or the lack of fusion of the metal powder. Location, size, density, pore shape are the major contributors to the variability of the fatigue strength. Despite major research efforts on parameter optimization and control in additive manufacturing, achieving a default-free part with a uniform microstructure is a remaining challenge. For this purpose, it is necessary to improve the understanding of the relation between the process parameters, the thermal history, the solidification, the resulting microstructure and the mechanical behavior.

The purpose of this work is to evaluate the effect of internal porosity on the fatigue strength of Inconel 718 obtained by the Selective Laser Melting process [1].

In this contribution, dedicated specimens with internal pores (spherical or lenticular shape) were manufactured [2]. Then, high cycle fatigue test under tension loading was performed and analyze to understand initiation mechanisms and highlight the debit in the fatigue strength limit. Fracture mechanics approach was used to correlate the test results and to determine the fatigue strength limit with the effect of porosities [3].

[1] D. Zhang, Z. Feng, C. Wang, W. Wang, Z. Liu, et W. Niu, « Comparison of microstructures and mechanical properties of Inconel 718 alloy processed by selective laser melting and casting », Materials Science and Engineering: A, vol. 724, p. 357‑367, 2018.

[2] O. Andreau, « Deterministic defect generation in selective laser melting: parametric optimization and control », Lasers in Manufacturing Conference 2017, 2017.

[3] E. Pessard, D. Bellett, F. Morel, et I. Koutiri, « A mechanistic approach to the Kitagawa–Takahashi diagram using a multiaxial probabilistic framework », Engineering Fracture Mechanics, vol. 109, p. 89‑104, 2013.

Speaker:
Additional Authors:
  • Hugo Sistach
    Safran Aircraft Engines