Chiara Scaramuzzi

Despite the advantages of powder bed fusion–laser beam (PBF-LB), Ti6Al4V components often exhibit high yield strength but limited ductility, which restricts their use in critical structural applications. This study aims to identify the most effective heat treatment to optimize the strength–ductility balance in Ti6Al4V parts produced by PBF-LB and to establish direct correlations between microstructural states, mechanical properties and corrosion behavior. Two distinct post-processing heat treatments were applied, specifically, the first at 500 °C for 5 h and the second at 800 °C for 2 h, both followed by air cooling. The microstructure was characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical behavior was assessed through Vickers microhardness testing and tensile testing, while corrosion resistance was evaluated via electrochemical measurements. Residual stress profiles were determined using the hole-drilling strain gauge method, in both as-built and heat-treated conditions. The as-built samples displayed a fully martensitic α′ structure with columnar grains aligned parallel to the laser scanning direction, resulting from rapid solidification. Heat treatment at 500 °C caused only partial decomposition of acicular martensite into substructures without altering its acicular morphology, leading to a strengthening effect alongside a reduction in ductility. Conversely, heat treatment at 800 °C offered the most balanced combination of strength and ductility among the conditions studied, albeit with a moderate reduction in corrosion resistance.

This study investigates the effect of heat build-up, as a function of different building modes and energy input, on the microstructure and mechanical properties of Al-Si10-Mg parts processed by Selective Laser Melting (SLM). Three different volumetric energy densities (67 J/mm ³ , 70 J/mm ³ and 86 J/mm ³ ) were applied for building samples. The building chamber was heated at 200 °C to reduce residual stress. The samples were processed in Horizontal (H) and Vertical (V) modes. The H and V samples were investigated using an Optical Microscope (OM), a Scanning Electron Microscope (SEM), x-ray diffraction (XRD), Vickers microhardness, and tensile tests. Moreover, the electrical conductivity (EC) of the samples was investigated . The amount, size, and morphology of the defects were also analyzed by Image J software. Different building modes significantly influenced the heat build-up, microstructure, and hardness at a set energy density. Vertical samples exhibited a coarser microstructure and reduced homogeneity along the growth direction ( z -axis) compared to horizontal samples. V samples also showed significant variations in microstructure and hardness along the z -axis, whereas H samples maintained greater uniformity. Furthermore, the percentage of defects increased in V samples and decreased in H samples with increasing heat input. Finally, after tensile test, a misalignment in mechanical response for H and V modes has been observed at all the energy densities except the lowest one. Graphical Abstract