PSI - Issue 53

S. Senol et al. / Procedia Structural Integrity 53 (2024) 12–28 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2021). A comprehensive overview of the available surface post-processing techniques that are applied to as-built samples can be found in (Maleki et al., 2021). It is also highlighted that these surface treatments can lead to not only modifications in surface roughness, but also residual stresses, hardness, grain size and near-surface porosity (Maleki et al., 2021; Ye et al., 2021). However, machining of aluminium MMC parts remains challenging. The combination of a rather soft and ductile Al-based matrix with a hard and stiff reinforcement phase makes that conventional machining tools wear rapidly and experience a limited tool life as well as material removal rate (MRR), and that machined parts display poor surface finish (Abrate & Walton, 1992b; Bains et al., 2016; Liao et al., 2019). As alternatives, non-conventional machining methods, such as electrical discharge machining (EDM) (Bains et al., 2016), laser (assisted), and abrasive waterjet machining (Abrate & Walton, 1992a; Pramanik, 2014)were applied to Al-based MMCs. Yet, each machining method has its benefits and disadvantages, and there is still a need for further improvement of the machinability of Al-based MMCs to exploit their full potential in structural and heat transfer applications, as highlighted in (Liao et al., 2019). As an alternative to applying a subtractive surface post-treatment subsequent to AM, hybrid methods are currently gaining interest (Dilberoglu et al., 2021; C. Liu et al., 2020; Manogharan et al., 2016; Riensche et al., 2022; Sealy et al., 2018; Zhu et al., 2013) for metals, focusing mostly on direct energy deposition (DED) and powder bed fusion (PBF) as AM techniques (Dilberoglu et al., 2021). Although there are various definitions for ‘hybrid methods’, it is used here to refer to the combination of an additive technique, L-PBF, with a subtractive method, laser ablation. Recently, a compelling hybrid alternative for improving surface quality of L-PBF parts in-process has been introduced by Metelkova et al. (Metelkova et al., 2020; Metelkova, Ordnung, et al., 2021; Metelkova, Vanmunster, et al., 2021): the dual-laser powder bed fusion (dL-PBF) process. This hybrid process can be grouped in ‘additive systems integrated with subtractive methods (AIMS)’ as defined by (Manogharan et al., 2015). The dL-PBF process enables in-process surface modification of up-facing inclined surfaces on L-PBF parts by means of 1) selective powder removal from the inclined surface covered with powder, thanks to laser-induced shock waves (LISW) and 2) subsequent re-melting (laser polishing). Moreover, its positive effect on surface quality and fatigue life of parts with up-facing inclined surfaces has been shown for commonly used Maraging steel and Titanium (Ordnung et al., 2022) and for a commercially available aluminium-based metal matrix composite (AM205) (Senol et al., 2023). In the current study, it is demonstrated that the dL-PBF approach allows to simultaneously build crack-free, high strength, hybrid particle reinforced (Ti+B 4 C)/Al-Cu-Mg parts via L-PBF, and to reduce the surface roughness of up facing inclined surfaces in-process, leading to extended fatigue life comparable to the conventionally machined condition. A comparative approach including AB, dL-PBF processed, EDM and milled surfaces allows revealing the beneficial effects of dL-PBF on surface quality and fatigue performance of L-PBF parts. 2. Experimental work 2.1. Material In this study, commercially available A2024-RAM2 ((Ti+B 4 C)/Al-Cu-Mg) (Elementum 3D, USA), aluminium based metal matrix composite (AMC) powder (particle sizes exhibiting D10 of 15 µm, D50 of 32 µm, and D90 of 52 µm) was used. The composite includes 2wt% ceramic reinforcement, which forms both ex-situ and in-situ, resulting in micrometer and nanometer-sized borides and carbides. 2.2. Sample production The powder was processed to build three-point bending fatigue (3PBF) samples by a dual laser system, integrated in an in-house customized ProX320 DMP (3D Systems) L-PBF machine equipped with both a continuous wave (CW) near-infrared (IR) (central wavelength of 1070 nm) fiber laser and an integrated nanosecond pulsed wave (PW) laser (pulse duration range of 2-250 ns). The nominal laser spot sizes are � / � � � 90 µ and � / � � � 50 µ for CW and PW laser, respectively. The CW laser was used to build the samples, while the PW laser was used to treat the sample top surfaces in-process, followed by re-melting via CW laser, as described in the following paragraph. The optimized L-PBF process parameters utilized for 3PBF sample fabrication were 260 W, 1200 mm/s, 0.125 mm, 0.03 mm, as CW laser power ( P ), scan speed ( ѵ ), hatch distance ( h ), layer thickness ( t ), respectively, utilizing