Effect of Surface Electropulsing Assisted Ultrasonic Impact Treatment on the Microstructure, Phase Composition, and Microhardness of 3D Printed Ti–6Al–4V Alloy

Abstract

X-ray diffraction analysis, transmission electron microscopy, and energy-dispersive analysis are used to study the phase and element compositions and microstructure of surface layers of the Ti–6Al–4V alloy prepared by additive 3D-printing and subjected to electropulsing assisted ultrasonic impact treatment (EAUIT). The firing pin material has been steel. It has been found that, in the course of EAUIT, the microalloying of the surface layer with iron to a depth of 5 µm takes place; the iron content reaches 22 at %. During the EAUIT, the nanocrystalline multiphase structure, which consists of titanium and iron oxides and metastable Ti4Fe and α -Ti phases, forms within the surface layer to 2 µm deep; under the nanocrystalline layer, the layer consisting of coarse-crystalline metastable Ti4Fe phase and amorphous phase is present. At a depth of more than 4 µm, the Ti4Fe phase with a submicrocrystalline structure forms; at a depth of 5 to 10 µm, the submicrocrystalline structure formed by (α-Ti + β-Ti) phases is present. Within α- and β-Ti grains, the nanocrystalline α -Ti phase is present. The microhardness of surface layer increases by 0.9–1.1 GPa as compared to that of untreated metal far from the surface.