Influence of microstructure evolution during thermal aging on tensile properties of β-type Ti-12V-2Fe-Al alloy

The evolution of the ω phase and its influence on tensile properties in β Ti-12V-2Fe-1Al alloys aged at temperature from 373 to 573 K were investigated. The results show that the formation of the thermal ω phase starts to take place at temperature between 393 and 423 K in the alloy. The growth of the thermal ω particles is accompanied by a rejection of V, Fe and Al solute atoms from the growing thermal ω particles into the surrounding β matrix. Tensile properties of the β Ti-12V-2Fe-Al alloy are strongly dependent on aging temperature. The plastic deformation mode changes from fully {332} deformation twinning in the ST alloy, to dislocation slip mixed with partially {332} twinning in the alloy aged at 393 K and to dislocation slip associated with stress-induced ω phase transformation in the alloy aged at 423 K. Particularly, the alloys aged at 523 K and above exhibit a brittle fracture without any elongation. It is suggested that the occurrence of the coherent elastic strain between the ω and β phase results in stabilization effect on the β matrix, which may account for the drastic change in plastic deformation mode and tensile properties in aged Ti-12V-2Fe-Al alloys with an increase of aging temperature