Synergistic enhancement of strength and ductility in Ti-22Al-25Nb alloy via high-laser-absorptivity μ-SLM induced dual-mode O-phase precipitation

Abstract

Ti₂AlNb-based alloys are promising lightweight materials for high-temperature aerospace applications. However, their performance is often hindered by Nb segregation and insufficient ductility. This study investigates the potential of micro-scale selective laser melting (μ-SLM) to overcome these issues by fabricating Ti-22Al-25Nb alloy from ultrafine powders. The ultrafine powder features an ultrathin oxide layer (∼4.67 nm), which facilitates a high laser absorptivity of 67.2%. This characteristic, coupled with the “point heat source” nature of μ-SLM, results in extreme cooling rates (∼10⁶ – 10⁷ K/s) that effectively suppress Nb segregation and brittle α₂ phase formation. The process induces a unique dual-mode O-phase precipitation: nano-sized O-phase (Immm) within grains and a quasi-continuous O-phase (Cmcm) network along grain boundaries. This microstructure, coupled with a high dislocation density (∼7.63×10³ µm⁻²) and substantial grain boundary strengthening, results in a remarkable synergy of strength and ductility, with a yield strength of ∼1040 MPa and an engineering tensile strain of ∼27%. Quantitative mechanistic analysis reveals that dispersion strengthening by intragranular nano-O particles, in tandem with dislocation strengthening, accounts for 76–80% of the total flow stress, supplemented by a ∼234 MPa increase from grain boundary strengthening. This study highlights the efficacy of μ-SLM in providing a novel metallurgical route to optimize microstructural evolution and enhance the mechanical response of Ti₂AlNb-based alloys.

Keywords

micron-scale selective laser melting / Ti₂AlNb / O-phase precipitation / dislocation strengthening / strength-ductility synergy

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