Manufacturing high strength Ti alloy with in-situ Cu alloying via directed energy deposition and evaluation of material properties

Abstract

In recent years, researchers have increasingly focused on alloy design in additive manufacturing (AM) to adjust the microstructure and improve the mechanical properties. The microstructure of columnar grains, strong texture, and chemical inhomogeneity in designed alloy exhibit anisotropic properties, which negatively affect the mechanical properties of the materials. One such material affected by this problem is titanium (Ti), which is known for its exceptional mechanical properties. Unlike other alloys, titanium lacks grain refiners that can ameliorate the columnar structure. Consequently, numerous studies are currently underway to refine the Ti grain through the addition of solute elements. In this study, Ti6Al4V with Cu element was deposited using the directed energy deposition (DED) process to investigate the feasibility of Ti6Al4V-xCu and analyze the effect of Cu addition. Ti6Al4V with Cu addition was successfully deposited and exhibited evenly distributed composition. In addition, finer grains were more created than the deposited Ti6Al4V by converting columnar to equiaxed grain due to the high cooling rate facilitated by high restriction factor Q of Cu. The deposited Ti6Al4V–4Cu of mechanical properties exhibited a 19 % increase in ultimate tensile strength, a 19 % increase in hardness at the top, and reduced elongation compared to the deposited Ti6Al4V, owing to the precipitation of Ti2Cu, grain refinement, and solid solution of Cu. However, although the hardness of the deposited Ti6Al4V–7Cu exhibited a 36 % increase in hardness at the top, Ti2Cu precipitate was generated significantly, which adversely exhibited a 26 % decrease in ultimate tensile strength compared to the deposited Ti6Al4V.