Offsize particle size utilization for laser powder bed fusion processing of plasma atomized Ti-6Al-4V powders: Impacts on part properties and powder safety

Abstract

Laser powder bed fusion (LPBF) is an additive method of choice for Ti-6Al-4V parts and utilizes powders in the range of 15–45 μm. Production of Ti-6Al-4V powders has low yield in this size range, and fine metal powders have the tendency to be dangerous, both via inhalation and via auto-ignition or explosions. This work attempts to determine if “offsize powders”, or coarser powder size distributions can produce viable parts for LPBF. Four plasma atomized powders with various oxygen contents and particle size distributions (PSD) were prepared by introducing powders in the 15–106 μm range. The powders were characterized for chemistry, and flowability then printed. Parts were characterized for strength, hardness, porosity surface roughness and dimensional accuracy. The offsize powders displayed comparable flowability and flow properties to that of the benchmark or traditionally used powder. The explosivity of the powders significantly decreased by lowering the fines fraction of the powder, resulting in up to an 84 % reduction in explosion severity (KST) and an increase in minimum ignition energy (MIE) of up to 3000 %. Within the printed parts, those produced by offsize powders displayed higher surface roughness, and lower yield strength and elongation to fracture. The increased surface roughness was attributed to the presence of coarser powders. The surface roughness of the produced samples increased with an increased coarse (>60 μm) fraction of the powders, leading to an increase in roughness of up to 48 % compared to the benchmark. Despite a reduced surface roughness, the produced parts were viable, with comparable mechanical properties: ± 50 MPa for both yield and tensile strength and within ±20 HV for hardness without any further printer-side optimization while also realizing significant benefits to powder safety.