Simultaneous enhancement of high-temperature performance and microstructural stability in an additively manufactured TiAl composite enabled by in-situ micro/nano precipitate networks

Conventional methods face inherent challenges in simultaneously enhancing the high-temperature strength and microstructural stability of TiAl alloys. To address this limitation, a Ti-48Al-8Nb (at.%) alloy reinforced by in-situ formed micro/nano precipitates was fabricated via directed energy deposition. The introduction of 1.0 at.% Si₃N₄ promoted the formation of an optimized, uniform equiaxed fully lamellar microstructure interlaced with a multiscale network of Ti₅Si₃ and Ti₂AlN precipitates. The developed metal matrix composite exhibits an ultimate tensile strength of 835 MPa at room temperature—an increase of 153 MPa over the unreinforced additively manufactured Ti-48Al-8Nb baseline alloy (682 MPa). Notably, it demonstrates exceptional strength retention at elevated temperatures, maintaining a UTS of 792 MPa at 850 °C, which surpasses that of the unreinforced counterpart (565 MPa) by 227 MPa. Furthermore, the composite displays outstanding microstructural stability, with no evidence of discontinuous coarsening or degradation after prolonged thermal exposure at 1100 °C for 200 h. This DED-based strategy, coupled with in-situ precipitation strengthening, establishes a new pathway for developing advanced TiAl composite that combine superior high-temperature performance with long-term microstructural integrity.