Extending powder particle size distribution of laser powder bed fusion Ti-6Al-4V: investigation of single tracks and multilayer experiments

Laser powder bed fusion (PBF-LB) is one of the most widespread additive manufacturing (AM) methods, spanning multiple industrialsectors such as medical, automotive and more recently aerospace. Current limitations to its large-scale adoption include low build rates,machining often required and consolidation via hot isostatic pressing (HIP). Productivity enhancement of PBF-LB has been investigated extensively and among the strategies adopted, that of combining high-speed parameters with HIP to achieve full density, has proven to beviable. This study puts forward a new approach for Ti-6Al-4V material, investigating if employing a wide particle size distribution (PSD)of the powder, with a range between 15 to 90μm, with a high layer thickness achieves comparable levels of bulk density, whilst improvingthe sustainability of the overall process and decreasing build times. If packing density can be improved by ensuring a more varied spreadof particle sizes, the thermal conductivity of the powder bed increases. Combination of small and large diameter particles would result in a reduction of the number of interparticle cavities upon powder spreading, therefore enhancing the contact and the efficiency of melting between neighbouring particles, upon laser heating. An EOS M290 machine was used to establish a processing window for the extendedPSD and increased layer thickness. Laser power, scanning velocity and hatch distance were varied to identify and exclude parametervalues that render extremes such as lack of fusion or keyholing defects. Single, multiple tracks and cubes were produced as part of a studythat aims to characterise the material’s response in terms of microstructure, defect density and hardness. It was possible to establish correspondence between tracks and cubes behaviour and isolate a design region that yielded minimal porosity.