Microstructure tailoring and superior strength‐ductility synergy in TiB/Ti‐55531 composites via isothermal forging

Abstract Isothermal forging is a crucial technique for finely tailoring the microstructure and achieving desirable mechanical properties in metastable β titanium alloys (β‐Ti), enabling the formation of complex components. However, research on isothermal forging of metastable β‐Ti based composites remains limited. Here, Ti‐55531 alloys and TiB/Ti‐55531 composites were isothermally forged in both (α + β) and β phase regions. The microstructure evolution, mechanical properties and strengthening/toughening mechanisms were thoroughly investigated. Isothermal forging promoted the refinement of matrix grains, homogenization of secondary α phase (α s ), and orderly arrangement of TiB whiskers. The forging temperature had a significant effect on the recrystallization behavior of β phase and the precipitation of primary α phase (α p ). The addition of TiB not only promoted discontinuous dynamic recrystallization but also facilitated the dispersion and precipitation of α p around TiB. Consequently, the mechanical properties of isothermal forged samples were significantly improved compared to the as‐casted ones, and the strength and ductility of the forged composites were both superior to those of the alloys. Specifically, the isothermal (α + β) forged composites achieved an excellent strength‐ductility balance, with a tensile strength of 1514 ± 16 MPa and a total elongation of 6.7% ± 0.2%. The strengthening and toughening mechanisms were mainly attributed to the hierarchical microstructure composed of intragranular α p , α s and α‐precipitate‐free zones, as well as the load‐bearing strengthening of TiB whiskers. Moreover, the α p closely adhered to TiB hindered crack propagation and relieved the stress concentration between transformed β structure and TiB by activating multi‐slip systems, thereby improving ductility and altering the fracture mode.