Microstructural evolution and mechanical properties of the in situ La₂O₃ particle-reinforced titanium alloy prepared by dual-wire-arc directed energy deposition

Abstract

TA15 titanium alloy components produced via wire-arc direct energy deposition (WA-DED) face challenges related to grain coarsening, suboptimal mechanical properties, and pronounced anisotropy. To address these issues, the current study employed a dual-wire-arc directed energy deposition (DWA-DED) approach to fabricating the alloys by introducing LaF3 quantitatively into the deposition metal using a metal cored wire. The incorporation of LaF3 was predicated on the in situ reaction: 6[O] + 6[H] + 2 LaF3 = La2O3 + 6HF. This reaction effectively removed [H] and [O] from the molten pool, diminishing the presence of the brittle intermetallic compounds and concurrently enhancing toughness. The addition of LaF3 resulted in a notable 56.8% increase in elongation and a 33.1% boost in impact toughness. Moreover, the DWA-DED quantitatively introduced [La], facilitating the precipitation of La2O3 particles. This precipitation reduced the size of primary columnar grains (PCGs) and promoted heterogeneous nucleation of α-laths. As a result, the elongation of the PCGs’ boundaries diversified the α phase transformation, resulting in the reduced multiple of uniform density (MUD) along the building direction. As a result, the isotropy ratio between vertical and horizontal directions also increased, underscoring the efficacy of LaF3 in mitigating anisotropic behaviour in WA-DEDed titanium alloys.