PSI - Issue 18

Matilde Scurria et al. / Procedia Structural Integrity 18 (2019) 586–593 Matilde Scurria, Benjamin Möller, Rainer Wagener, Thilo Bein/ Structural Integrity Procedia 00 (2019) 000–000

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4. Conclusions The cyclic stress-strain behavior of additively manufactured Inconel ® 718, with respect to different build orientations and subsequent heat treatments, has been investigated. Based on the results achieved, it can be stated that, regardless of the heat treatment, additively manufactured Inconel ® 718 presents an anisotropic behavior for cyclic deformations limited to the linear-elastic regime. In particular, the Young’s modulus is higher when the loading direction is rotated by 45° with respect to the build direction, compared to the configuration in which load path and building direction are aligned (Z). It has been demonstrated that the cyclic behavior is independent of the heat treatment along the build direction Z, while, along XZ, it varies significantly. In fact, along XZ, as a consequence of the heat treatment with a maximum temperature of 650 °C (A), the cyclic stress-strain hysteresis is wider and crosses the ordinate at higher maximal and lower minimal values of the stress. For the same maximum total strain, the maximum tensile stress reached for heat treatment ‘A’ results in a lower value of the stress compared to the heat treatment with a maximum temperature of 760 °C (B) or 965 °C (C). For higher values of the strain amplitude, the cyclic stress-strain hysteresis of heat treatment ‘C’ tends to behave like ‘A’, while the hystereses for B are stretched to higher values of the stress, in both the first and third quadrants. This affects the fatigue life in a way that the material, where the maximum tensile stress (in correspondence with the same maximum total strain) is higher, results in a lower number of cycles to crack initiation. Also, if the maximum stress values coincide, lower numbers of cycles to crack initiation correspond to the material with wider stress-strain hysteresis loops. The Z direction, as well as the heat treatment ‘C’, result in higher fatigue strength (see Fig.4), even if this effect becomes less evident as we move to higher strain amplitudes and the scatter is narrower. Finally, the heat treatment ‘C’ causes a modification and redistribution of the microstructure inside the material, leading to an isotropic material behavior for high values of the strain amplitude (  a,t = 0.8%). Acknowledgements The research and development project ‘BadgeB’ that forms the basis for this publication is funded within the scope of the “Additive Fertigung – Individualisierte Produkte, komplexe Massenprodukte, innovatiove Materialien” (Pro_Mat_3D) by the Federal Ministry of Education and Research. The project BadgeB is managed by the KIT project management agency “Projektträger Karlsruhe – Produktion und Fertigungstechnologien”. The authors are responsible for the content of this publication. References Active Standard, A. S. T. M., “F2792 Standard Terminology for Additive Manufacturing Technologies”, West Conshohocken: ASTM Int. (2012). Calignano, F., "Design optimization of supports for overhanging structures in aluminum and titanium alloys by selective laser melting", Materials & Design 64 (2014) pp. 203-213. Deng, D., Peng, R. L., Brodin, H., & Moverare, J., “Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments”, Materials Science and Engineering : A, 713 (2018), pp. 294-306. Hell, M., et al. , "Fatigue Life Design of Components under Variable Amplitude Loading with Respect to Cyclic Material Behaviour." Procedia Engineering 101 (2015), pp. 194-202. Landgraf, R. W., Morrow, J D., Endo, T., "Determination of the cyclic stress-strain curve", Journal of Materials 4.1 (1969): 176-188. VDI guideline 3405; Blatt 3, „Additive Fertigungsverfahren – Konstruktionsempfehlungen für die Bauteilfertigung mit Laser-Sintern und Laser- Strahlschmelzen“ (2015). Mishurova, T., et al. , "The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts", Metallurgical and Materials Transactions A 49.7 (2018):, pp. 3038-3046. Morrow, J.D., "Cyclic plastic strain energy and fatigue of metals", Internal friction, damping, and cyclic plasticity. ASTM International , STP No. 378 (1965): pp. 45-87 Poyraz, Ö., et al. , "Investigation of support structures for direct metal laser sintering (DMLS) of IN625 parts", Proceedings of the Solid Freeform Fabrication Symposium , Austin, Texas, USA. 2015. Rahman, M., Seah, W. K. H., & Teo, T. T., „The machinability of Inconel 718”, Journal of Materials Processing Technology , 63(1997) 1-3, pp. 199-204. Ramberg, W., Osgood, W.R., "Description of stress-strain curves by three parameters", NACA Technical Note No. 902 (1943). Scurria, M., Möller, B., Wagener, R., Pena, J., and Bein, T. , “Effects of Surface Preparation, Support Structures and Build Orientation on the Cyclic Stress-Strain Behavior of Inconel ® 718 Produced by SLM” SAE Technical Paper 2019-01-0918 (2019).