PSI - Issue 37

G. Macoretta et al. / Procedia Structural Integrity 37 (2022) 632–643

633

2

G. Macoretta, B. D. Monelli / Structural Integrity Procedia 00 (2019) 000 – 000

© 2022 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira Keywords: SLM; fatigue; process parameters; roughness; HCF; porosity; productivity; Inconel 718 © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira 1. Introduction Selective Laser Melting of metallic materials is emerging as a technology suitable for the industrial production of critical components. The possibility to manufacture complex geometries, the possibility to produce only a limited number of components, the minimization of the design-to-production lead time, and the scarp reduction are some of the key advantages of the technology. However, it is well known that the major shortcomings of the SLM technology are the reduction in the fatigue performances of the material, compared to wrought condition, and the lower productivity rate. The challenge to increase the process productivity can be afforded by parallelizing the production on several machines, by introducing additional laser beams within the same machine or by adopting a set of process parameters aimed to increase the productivity rate, even at the expense of a reduction of the mechanical properties of the material if they are employed in a non-critical area of the component. The first two ways can be more effective but are more expensive as well. Based on the analytical model proposed by Moda (2021), and on the feasible region investigations carried out in the literature, Clymer et al. (2017), Guo et al. (2020), Ravichander et al. (2020), Wan et al. (2018), and Yakout et al. (2020), it is possible to define a preliminary analytical feasible region for the SLM of the alloy Inconel 718. An analytical knowledge of the process feasible region is indeed crucial not only for reducing the number of experiments needed to reach the desired material properties but also to have a theoretical, even if simplified, framework that can help the comprehension of the observed phenomena. On its base, two sets of SLM process parameters aimed to enhance the system productivity by increasing printed volume per unit of time, while complying with the constraints of the material feasible region, were devised. In the present paper, it is presented a preliminary experimental investigation on the effects on the fatigue behavior of two sets of process parameters devised to significantly increase process productivity rate, along with investigations on the material microstructure and surface roughness, and fractographic analyses.

Nomenclature A r

Aspect ratio of the meltpool

BD Build direction HCF High Cycle Fatigue SLM

Selective Laser Melting

2. Material and methods 2.1. SLM process

The specimens were produced by Selective Laser Melting (SLM) employing a standard Inconel 718 alloy powder provided by Heraeus Electro-Nite GmbH & Co. KG (Hanau, Germany), featuring a chemical composition in compliance with the ASTM B637 standard, reported in Table 1. The powder, produced by a Vacuum Inert Gas Atomization (VIGA) process, featured a Particle Size Distribution (PSD) comprised between 13 μ m (D10) and 53 μ m (D90). The specimens were produced by using a Renishaw RenAM 500E SLM machine (Renishaw S.p.A., Torino, Italy), characterized by a maximum laser power of 500W and a maximum laser speed of 7 m/s, installed in the “Metal Additive Manufacturing” laboratory of the University of Pisa. The printer has the capability of using both a pulsed