PSI - Issue 77

V. Kroužecký et al. / Procedia Structural Integrity 77 (2026) 161 – 169 Vít Kroužecký / Structural Integrity Procedia 00 (2026) 000 – 000

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1. Introduction Selective laser melting (SLM) is a powder-bed fusion (PBF) technology that builds metallic parts by spreading a thin layer of metal powder and selectively melting regions with a calibrated laser, layer by layer in a protective atmosphere to form complex 3D geometries (Dejene and Lemu, 2023; Lin, 2021). The main process variables — layer thickness, laser power, scan speed, and hatch spacing — together with the chosen scan strategy, govern melt-pool dynamics, densification, and residual stresses. Careful parameter control is therefore central to final part quality (Dejene and Lemu, 2023; Li, 2023; Pagac et al., 2021). Common materials (e.g., Ti-6Al-4V, 316L) exhibit microstructural evolution and property sensitivity to cooling rates and thermal history (Abu Zaki et al., 2024; Dejene and Lemu, 2023; Kim et al., 2023). Despite rapid progress, SLM still faces key challenges, including distortion, warpage, porosity, and high surface roughness. Current research focuses on build orientation, defect prediction, and in situ monitoring to mitigate these limitations (Choiron et al., 2025; Pagac et al., 2021; Wu et al., 2021). Although SLM enables the fabrication of advanced lattice and TPMS architectures, post-processing such as heat treatment or surface finishing is often required to reach application-ready properties (Faisal et al., 2022; Hui et al., 2021; Kim et al., 2023). The influence of downward-facing surfaces in the Selective Laser Melting (SLM) process has received significant attention due to its strong impact on the quality and mechanical properties of manufactured parts. Piscopo et al., 2019 reported that such surfaces are prone to distortion and scale formation, especially at inclination angles around 35° and for unsupported overhangs exceeding 7.5 – 9 mm. Defects tend to accumulate at surface edges, reducing the mechanical integrity of the part. Shen et al., 2020, who demonstrated that varying build angles result in different microstructures, leading to anisotropic material behavior. Downward-facing surfaces generally exhibit inferior mechanical properties compared to upward-facing ones, with reduced tensile strength and fatigue resistance, which is critical for applications requiring high reliability. Complementing these findings, (Wang et al., 2022) showed that build angle and associated surface roughness play a key role not only in determining mechanical performance but also in corrosion resistance. They highlighted that optimization of build orientation can mitigate the adverse effects of surface roughness, which are most pronounced on downward-facing surfaces. Optimized build orientation and process parameters (e.g., laser power, scan speed, hatch spacing) have been shown to reduce surface roughness and improve mechanical integrity, especially in downward-facing regions. Collectively, these studies highlight the crucial role of build orientation and process control for ensuring the structural integrity of SLM components. Powders for selective laser melting (SLM) of 316L stainless steel critically determine part density, surface quality, and mechanical performance. Gas-atomized, spherical 316L powders with a typical particle size range of 5 to 50 micrometers promote uniform layer deposition and high packing density, supporting near-full density parts; however, powder chemistry (oxygen, nitrogen) and particle size distribution (PSD) can significantly influence densification and corrosion behavior (Casati et al., 2016; Cui et al., 2019). PSDs with an excess of fine particles can enhance bed density but may impair flowability and process stability, whereas well-controlled bimodal distributions can improve both density and surface finish (Zhai et al., 2022; Du et al., 2019; Spierings et al., 2011). Powder layer density measurements are important predictors of final part density and microstructure, guiding layer thickness and recoater design (Choi et al., 2017). Powder feedstock composition — such as nitrogen enrichment or additions of chromium nitride/carbide — can significantly influence flowability, corrosion resistance, and wear properties. However, these modifications may introduce trade-offs in processability. (Cui et al., 2019; Zhai et al., 2022). Surface quality and microstructure in as-built 316L parts are governed by melt-pool dynamics dictated by PSD and flowability. Microstructural studies report γ -austenite-dominated structures with orientation-dependent morphology, influenced by powder characteristics and processing parameters (Brytan, 2017; Zhai et al., 2022). Collectively, optimizing powder production (morphology, oxygen/nitrogen levels), PSD, and additive content is essential to realize robust, high-density 316L SLM parts for aerospace, biomedical, and energy applications (Chen et al., 2018; Choi et al., 2017; Spierings et al., 2011; Vukkum et al., 2022) SLM-316L parts exhibit high strength with pronounced anisotropy introduced by rapid solidification, melt-pool texture, and porosity. The tensile strength, yield stress, and ductility depend significantly on laser power, scan speed, layer thickness, and scan strategy, necessitating careful parameter optimization to enhance bonding and reduce defects