Investigation of Ti6Al4V Alloy Fabricated by LPBF with Thick Layer: Role of Scanning Speed in Defect Control and Mechanical Performance

Aiming at the contradiction between forming quality and efficiency in the existing research on thick-layer laser powder bed fusion (LPBF) manufacturing of Ti6Al4V, this study focused on the influence of near-circular keyhole defects caused by scanning speed on the short-term mechanical properties of Ti6Al4V alloy manufactured by high-efficiency LPBF with a 100 μm layer thickness, the build rate of which reached 14 mm3/s. When the scanning speed decreased to 800 mm/s, the relative density decreased from 99.87% to 99.27%, and the maximum pore size increased from 19.6 μm to 87.2 μm. Under the conditions of high relative density (above 99.8%) and maximum pore size less than 20 μm, the annealed Ti6Al4V samples could achieve a tensile strength of 1009.7 MPa, a yield strength of 914.0 MPa, an elongation of 15.2%, and an impact toughness of 41.71 J/cm2. With the increase in porosity and a maximum pore size exceeding 50 μm, the tensile strength became more unstable and exhibited a declining trend, while the impact toughness decreased by more than 5%. This is mainly attributed to the stress concentration around large-sized pores, leading to the easy generation of long and deep cracks at the edges and reducing the material’s ability to resist crack initiation and propagation.