Unleashing superior strength and ductility in additively manufactured β-titanium alloys through spinodal decomposition

To address the strength-ductility trade-off issue caused by precipitate strengthening in metastable β-titanium alloys, this study proposes an innovative strategy, i.e., tailoring the spinodal decomposition microstructure in the alloy Ti-15Mo-3Al-2.7Nb-0.2Si using laser powder bed fusion (LPBF) to achieve control of dislocation behavior. Microstructural analysis revealed that the best LPBF alloy in this work, designated A-E83, with an energy input of 83 J mm −3 , exhibited a single-phase body-centered cubic structure containing a high density of dislocations, fine-grained morphology, and uniform multiscale spinodal decomposition structures (modulation wavelengths: 50.9±12.9 nm and 546.7±168.7 nm wavelengths), characterized by chemical composition and lattice strain inhomogeneity. These microstructural features enable a superior strength-ductility combination at room temperature, i.e., a yield strength of 1120 ± 34 MPa, an ultimate tensile strength of 1177±13 MPa, and an elongation of 35.0±2.2%, representing improvements of 31.3%, 29.8%, and 127.3% over the traditional solution treated + water quenched (ST-WQ) alloy, respectively. Quantitative analysis shows that the improvement in strength in the A-E83 alloy compared to the ST-WQ alloy originates from three mechanisms: dislocation strengthening (23 MPa, 8.3% contribution), grain refinement strengthening (77 MPa, 27.9%), and most importantly spinodal decomposition strengthening (176 MPa, 63.8%). Unlike the deformation mechanism of the ST-WQ specimen that relies on the slip in the BCC matrix, in the A-E83 specimen, the presence of homogeneous spinodal decomposition structure not only slows down dislocation motion but also triggers the formation and multiplication of dislocation loops, thereby strengthening the alloy while achieving uniform plastic deformation. This work demonstrates LPBF-tailored spinodal decomposition can be used as an effective strategy to simultaneously enhance the strength and ductility in metastable β-Ti alloys, and thus offers valuable insights for advanced metallic material design.