Effect of powder characteristics on layer density, defects, and tensile properties of Ti-6Al-4V via laser powder bed fusion: establishing benchmark parameters for quality

Abstract Feedstock powder characteristics affect the quality of metal parts manufactured by laser-based powder bed fusion of metals (PBF-LB/M). However, identifying the decisive powder characteristics remains challenging due to the complexity of the PBF-LB/M process and lack of in-situ, process-relevant data. This study assesses four gas-atomised (GA) virgin Ti-6Al-4V powders using an SLM Solutions ® system. The surface chemistry, morphological constituents, particle size distribution (PSD) and rheological properties of each powder are investigated. Furthermore, using a powder-bed capsule approach, combined with micro-computed tomography (μCT) analyses, the powder-bed layer density (ρ layer ) averaged over 1134 layers in real PBF-LB/M is determined for respective powders and correlated to the defects and tensile properties of the as-printed Ti-6Al-4V specimens. We demonstrate that ρ layer is critical to the as-printed quality and propose a benchmark ρ layer of at least 65% of the theoretical density of Ti-6Al-4V to achieve high-quality builds. Additionally, it was found that none of the conventional powder morphological and rheological properties, such as apparent density, tap density, and angle of repose, are sufficiently informative as decisive powder characteristics for predicting PBF-LB/M quality. We further propose that, within the specified powder size range, the powder parameters D[3,2] (a particle surface area-based mean diameter) and D[4,3] (a particle volume-based mean diameter) should be tailored to the stabilised layer thickness of the selected PBF-LB/M process as supplementary benchmark parameters. This layer thickness can be calculated from the nominal layer thickness and ρ layer using an analytical model. The proposed powder-bed capsule-μCT approach can serve as a unique powder assessment method for PBF-LB/M. This study also investigates the role of fine powder particles within the PSD and their impact on packing density, revealing that an optimal balance of fine particles is crucial for enhancing powder-bed layer density while mitigating the risks associated with agglomeration and instability.