In-situ tensile SEM investigation on the high-temperature tensile properties and deformation mechanism in Ti-6Al-4V alloy with different microstructure types

To reveal the influence of microstructure types on high-temperature tensile properties and deformation mechanism in TC4 titanium alloy, this work conducted tensile tests and in-situ tensile SEM observation at 350°C on the as-received equiaxed microstructure (EM), the designed lamellar microstructure (LM) and two types (I and Ⅱ) of bimodal microstructures with similar equiaxed α (α eq ) phase content. Wherein, Type I had a colony structure consisting of lamellar α and interlayer β. Type Ⅱ had a bilamellar structure consisting of basketweave-α and dispersed α. The high-temperature tensile and in-situ tensile results showed that Types I and Ⅱ had higher strength than EM and LM, which could be attributed to that more interfaces fabricated in Types I and Ⅱ to restrict slip transfer and hinder dislocation movement. Moreover, Type Ⅱ had higher strength than Type Ⅰ due to precipitation strengthening. The EM had the highest plasticity, which could be attributed to that α eq grains could accommodate more plastic deformation through the initiation of multiple slip and twins. The LM had the lowest strength and plasticity. This is because during early deformation, coarse α-colonies in the LM tended to induce crack nucleation at α-colony/colony and α-colony/grain boundary α interfaces, which would be detrimental to strength and plasticity. Additionally, compared to room-temperature tensile deformation, high-temperature tensile deformation exhibited better work hardening ability with increasing strain due to the formation of massive dislocation networks, dislocation tangles and twins.