Laser powder bed fusion of 316L stainless steel/Al2O3 nanocomposites: Taguchi analysis and material characterization

Abstract

This work deals with the mechanical properties and microstructure of additively manufactured (AM) 316L stainless steels strengthened with Al2O3 nanoparticles. At first, the critical processing parameters of laser powder bed fusion (LPBF) were optimized using Taguchi analysis in terms of laser power (180–210 W), scan speed (90–270 mm/s), hatch space (200–300 µm), and layer thickness (20–40 µm) to obtain materials with the highest density. Based on the modeling predictions and experimental findings, energy density was determined as a critical factor in controlling the integrity of deposited structures and their cracking behavior. The microstructural features and mechanical properties of the produced nanocomposites were characterized afterward. Grain structural aspects and crystallographic textural evolution across different sections of the printed nanocomposites, along with the distribution of reinforcing alumina nanoparticles, were studied using optical microscopy (OM), channeling contrast field emission-scanning electron microscopy (FE-SEM) imaging, electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM) analyses. The fabricated materials' mechanical properties were also evaluated using indentation micro-hardness testing across the printed cubic structures. Trends revealed a considerable grain structural refinement down to the nanometric scale by incorporation and uniform distribution of alumina nanoparticles depending on the selective laser melting (SLM) processing parameters. This consequently improved the hardness of the materials up to around 270 Vickers. The role of unstable Al2O3 nanoparticles would directly strengthen the stainless steel metal matrix by generating new in-situ agents during LPBF. Moreover, the crucial indirect influence was discovered in controlling the involved solidification mechanisms and subsequent microstructural features.