PSI - Issue 41

Saveria Spiller et al. / Procedia Structural Integrity 41 (2022) 158–174 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000–000

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et al., 2020; Sadaf et al., 2021b; Suwanpreecha et al., 2021), surface roughness assessment (Galati et al., 2019), porosity analysis employing optical microscope, SEM (Caminero et al., 2021; Hassan et al., 2021; Kurose et al., 2020; Sadaf et al., 2021; Suwanpreecha et al., 2021), or computer tomography (Damon et al., 2019). Finally, the parts undergo static tests, either tensile or bending tests (Caminero et al., 2021; Hassan et al., 2021; Henry et al., 2021; Kurose et al., 2020; Rosnitschek et al., 2021; Sadaf et al., 2021; Suwanpreecha et al., 2021; Thompson et al., 2019; Liu et al., 2020), to study the fracture surface and assess the statical mechanical properties. Sometimes mechanical properties of MEAM parts are compared with other techniques (Caminero et al., 2021; Damon et al., 2019; Gong et al., 2019; Liu et al., 2020; Sadaf et al., 2021; Safka et al., 2020; Tosto et al., 2021). 5.1. Prameters optimization The relation between porosity and mechanical properties is one of the central themes of this whole review. The final density usually achieved by MEAM parts is lower compared to other AM techniques. In Fig. 8. Relative density data of different works some data about relative density are collected, both for 316L and 17-4 PH parts with the relative density values ranging between 92% and 98%.

Fig. 8. Relative density data of different works

The issue with a low-density part is that the mechanical properties are affected negatively. For example, Liu et al. (2020) printed and sintered specimens to perform tensile tests out of a filament composed of the 88wt% of 316L metal powder. The resulting mechanical properties were found to be lower compared to both the standard AISI 316L and parts fabricated through SLM. The yield stress and ultimate tensile strength were reported to be 194 MPa and 441 MPa, respectively 5.37% and 14.37% lower compared to standard AISI 316L properties. The authors explained this difference as related to the high porosity level of the MEAM parts. A similar conclusion was drawn by Thompson et al. (2019), where three-point bending tests were performed. The stress-deflection curves obtained showed that the strength of the printed components is lower compared to the counterparts’ specimens obtained from conventional 316L sheets. The reasons indicated by the authors are the following: first, the porosity strongly affects the mechanical properties and aggravates the discrepancy of performances among printed specimens. The pores' size and distribution do not follow a specific trend and the scatter between the stress-strain curves of different specimens proves it. The second reason indicated by Thompson et al. (2019) is a microstructural aspect: the grain size growth provoked by the thermal process is not beneficial for the mechanical properties. A similar scatter of mechanical properties was also observed by Gonzalez-Gutierrez et al. (2019). In this work 17-4 PH parts were printed to perform tensile tests. The specimen with maximum strain at break (5.71%) reached 729 MPa as UTS during the