Oxygen scavenging-driven plastic response of α2-Ti3Al in dual-phase TiAl alloy

Improving the room-temperature ductility of TiAl alloys is crucial for their broader structural applications. However, excessive interstitial oxygen (O) contamination intensifies the strain incompatibility between α 2 and γ phases, severely impairing the overall mechanical properties. Here, we propose a novel calcium (Ca)-based O-scavenging strategy to enhance the ductility of powder metallurgy (PM) TiAl alloys by introducing trace CaH 2 . A duplex oxide layer composed of outer Al 2 O 3 layer and inner TiO 2 layer, was identified on the surface of TiAl powder and has the thickness of ∼9.13 ± 0.35 nm. Upon the dissolution of oxide layer (∼824°C), O is released and readily diffuses into the matrix as interstitials, where it becomes effectively irretrievable. CaH 2 can react with the oxide layer below its decomposition temperature (∼791°C), effectively immobilizing O as nanoscale CaO particles, thereby suppressing O dissolution into α 2 phase and mitigating the lattice distortion. The resulting purification of the α 2 phase decreases the critical resolved shear stress (CRSS) required for basal slip. During deformation, deformation twins in the adjacent γ grains facilitate the activation of -type dislocations within α 2 phase, thereby enhancing its plasticity and improving interphase strain compatibility. Additionally, the in-situ formed CaO particles contribute to the dispersion strengthening. As a result, this trace Ca-based deoxidation strategy nearly doubles the room-temperature total elongation of PM Ti4822 alloys while retaining an ultimate tensile strength of 580 MPa, even at a relatively high O content (∼1520 ppm).