Strength and ductility-related properties of ultrafine grained two-phase titanium alloy produced by warm multiaxial forging

The most important room temperature mechanical properties of two-phase Ti–6Al–4V alloy with ultrafine grained microstructure were studied in the present work. Bulk preforms of the alloy with ultrafine grained microstructure were produced by warm multiaxial forging. The final structure consisted of alpha and beta particles with size of 150–500 nm depending on deformation temperature. The mechanical properties of ultrafine grained material were carried out in comparison with conventionally heat-strengthened condition of the alloy. Room-temperature strength of the ultrafine grained material was found to be 16–33% higher than that of the heat-strengthened alloy. However, ductility-related properties including tensile elongation, impact toughness, fatigue crack growth resistance and fracture toughness noticeably decreased with decreasing grain size. The efforts to increase ductility the ultrafine grained alloy by annealing was restricted by rather intensive softening of the material. Considerable enhancement of ductility of the alloy with a bi-modal microstructure consisting of large primary alpha in UFG alpha/beta matrix was shown.

► Strength of Ti–6Al–4V increases up to 33% due to grain refinement to UFG regime.
► Ductility-related properties decrease with decreasing grain size to UFG regime.
► Increasing ductility of UFG alloy by annealing is limited by intensive softening.
► Large alpha particles in UFG matrix enhance ductility without strength loss.