In-situ alloying of a fine grained fully equiaxed Ti-based alloy via electron beam powder bed fusion additive manufacturing process

Alloy design using Additive Manufacturing (AM) methods is an interesting research area attracting the attention of researchers across the world. Formation of strong texture, columnar grains, and chemical inhomogeneity in AM-designed alloys are among the serious challenges dealt with in various research works. This paper addresses these challenges for the first time for a Ti6Al4V-7Cu alloy produced via Electron Beam Powder Bed Fusion (EB-PBF) method following an in-situ alloying approach. In this work, a mixture of Ti6Al4V and elemental Cu powders was used as the feedstock. The results showed a relatively homogenous Cu distribution in the product due to the large melt pool created during the EB-PBF process, a development indicating the method's applicability for in-situ alloying and alloy design. The prior beta columnar grains were effectively converted into equiaxed grains due to a constitutionally supercooled zone created by the rejection of Cu solutes in front of the solidification front and a relatively lower thermal gradient during EB-PBF compared with other AM processes. The addition of Cu enhanced the microhardness of Ti6Al4V, which could be considered an outcome of equiaxed grain formation, solid solution strengthening mechanism, and Ti2Cu intermetallic precipitation.