Surface modification of EBF3-Fabricated Ti–6Al–4V parts by ultrasonic impact treatment

Mechanical post-processing of 3D-printed components are required due to their poor surface finish, non-uniform microstructure and high residual stresses. Ultrasonic impact treatment can be successfully used for surface modification of Ti–6Al–4V titanium alloy parts manufactured by electron beam free-form fabrication. The gradient microstructure of the surface layers, produced in 3D-printed Ti–6Al–4V parts under ultrasonic impact treatment, was revealed using transmission electron microscopy. Non-equiaxial nanosized α-Ti grains were revealed in the outmost surface layer of 5–10 µm thick. α-Ti crystal grains with average size 150 nm are observed at depth of 20 µm beneath the specimen's surface. Finally, the average size of α-phase grains at a depth of 35 μm below the surface is equal to 400 nm. Orthorhombic α″ martensitic phase within fine α-Ti grains is observed. The mechanism of α″ phase formation during ultrasonic impact treatment is discussed.