EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Scope of this work is to overview the influence of a multiple step electrochemical surface treatment, heat treatment and print orientation on microstructure and mechanical properties of Ti 6Al 4V processed by laser powder bed fusion (L-PBF). Experiments were carried out from a first patch, after using virgin powder to avoid powder quality and morphology quality.
First tests include density and surface roughness to optimize process parameters using design of experiment. Mechanical test specimens for tensile, notched bar impact (charpy) and compression tests were build in three different orientations, vertically, horizontally and leaned at 45° to the build plate. Subsequently, thermal treatments stress relief, furnace annealing and hot isostatic pressing were performed to determine the changes on microstructure and mechanical properties. In addition to as-build samples, mechanical machining and electrochemical polishing surface treatment were applied to investigate the influence of surface roughness.
As-build specimen shows little anisotropy in yield- and tensile strength, but a strong influence on the necking and a brittle fracture behavior due to their martensitic microstructure. Heat treatment can increase ductility and further decrease strength anisotropy with both, furnace annealing and HIP showing similar results for tensile properties. Electrochemical polishing is a viable way to decrease surface roughness (down to a Ra of 1µm and Rz around 4µm from 7.5µm and 40µm respectively for vertical parts) and drastically increasing fracture necking and its isotropy compared to as-built parts from 4% to over 30%.