Bi microalloying enhances interface regulation and strength–ductility balance in TiB-reinforced Ti–6Al–4V composites

TiB-reinforced Ti–6Al–4V composites containing trace Bi were prepared by hot-press sintering and spark plasma sintering at the same temperature (950 °C), holding time (1 h), and pressure, to clarify how the sintering route affects phase constitution, interfacial characteristics, and tensile properties. Compared with hot-press sintering, spark plasma sintering more effectively suppresses excessive Ti–Bi reactions, promotes a more homogeneous phase distribution, and facilitates the formation of finely dispersed TiB reinforcements. Electron backscatter diffraction phase mapping indicates fewer Bi-rich indexed regions in the spark plasma sintering sample than in the hot-press sintering sample, while TiB is detected in the spark plasma sintering sample. As a result, the spark plasma sintering-processed composite exhibits superior tensile properties, with a tensile strength of 1251 MPa and an elongation of 8.84%. Molecular dynamics simulations performed at 1223.15 K suggest that Bi promotes B diffusion, with the effective diffusion coefficient increasing by 18.4%. These results help explain the distinct phase evolution and interfacial regulation observed during SPS, demonstrating that Bi microalloying combined with spark plasma sintering is an effective strategy for improving the balance between strength and ductility in in-situ TiBw/TC4 composites.