Enhancing Compressive Stress–Strain of Ti55531 Alloy via La-Rich Nanoscale Structure at Grain Boundaries

For multi-component Ti alloys, their room temperature compressive stress–strain are relatively low. Addition of La can promote the formation of α phase. The addition of 0.1 wt.% La into Ti55531 alloy results in the formation of nanoscale needle-like structure (α phase) along grain boundaries with a spacing of 9.66 nm and thereby enhances the compressive stress–strain of Ti55531-0.1La (wt.%) alloy with an ultimate compressive plastic strain of 51.5 ± 6.3% and a compressive strength of 2267 ± 58.6 MPa. La-rich particles (La₂O₃) with a size of 40-100 nm were also observed along grain boundaries. Both nanoscale α phase and La-rich particles are tightly bounded together at the interface with a semi-coherent structure to suppress the microcracks expansion. The proposed method using La₂O₃ triggering a nanoneedle-like structure at grain boundaries provides a novel strategy to enhance compressive stress–strain in the multi-component Ti alloy.