Process–microstructure–property relationships in Ti–Al alloys fabricated by laser directed energy deposition of Ti6Al4V and al powders

Abstract

The purpose of this research is to investigate the formation of TiAl phases in additively manufactured samples using a combination of Ti6Al4V and Al powders mixed in a 3.3:1.7ratio. Thin-walled samples were fabricated using direct laser deposition (DED) at various laser beam scanning speeds (5, 10, and 20 mm/s). The study examines the influence of laser scanning speed on the microstructure, phase formation, and hardness of the samples. The principal results indicate that the formation of TiAl phases is evident in the samples, with the presence of α2-Ti3Al, β0-TiAl, and γ-TiAl phases. At a scanning speed of 20 mm/s, the β-titanium phase is still present, while at lower speeds (10 mm/s and 5 mm/s), the β-Ti phase disappears, and an increase in Ti-Al phases is observed. The hardness of the samples increases from the region closest to the substrate to the region furthest from it, with average hardness values increasing as the laser beam pass speed increases. This is attributed to the decrease in energy density and the variation in thermal cycles experienced by the deposited layers. The laser beam pass speed significantly affects the microstructure and phase formation in additively manufactured TiAl samples. Lower scanning speeds result in more frequent and prolonged thermal cycles, facilitating complete phase transformations and the formation of a more homogeneous microstructure. The differences in thermal cycles experienced by the layers influence the hardness and phase distribution within the samples.