Effect of phase content on mechanical properties and deformation mechanism in TC21 titanium alloy: An in-situ tensile investigation

This work fabricated a series of microstructures consisting of different equiaxed α (αeq) and β phase contents to investigated the effect of phase content on mechanical properties and deformation mechanism, including slip initiation, slip transfer, stress-induced martensite (SIM) and crack nucleation of TC21 titanium alloy. The results show that, with the decrease of αeq phase content, the YS of the alloy firstly decreases and then increases, the UTS gradually increases, and the EL gradually decreases. The significant variation of mechanical properties is closely related to the deformation mechanism of microstructures with different αeq phase contents. In sample with high αeq phase content, αeq phase is deformed by slip prior to β phase, and with the increase of strain, β phase can coordinate deformation by slip initiation and exhibits a better ability to coordinate plastic deformation. In samples with medium αeq phase content, the stability of β phase decreases, slip in αeq grain and SIM in β grain can be initiated simultaneously. However, the formation of SIM would harden β phase, and with the increase of strain, it would restrain the ability of β phase to further coordinate plastic deformation. In samples with low αeq phase content, the stability of β phase decreases sharply, which could induce the precipitation of fine-lamellar secondary α (αs) and acicular martensite α'' in β grain during annealing. These precipitated αs and α'' can not only inhibit the formation of SIM, but also dramatically reduce the ability of β phase to coordinate plastic deformation. Meanwhile, the evolution of deformation mechanism in different samples can significantly influence the crack nucleation location (slip band or αeq/β interface) during deformation. This paper analyzes in detail the effect of αeq phase content on mechanical properties of TC21 titanium alloy based on deformation mechanism, it would contribute to the establishment of a relationship among phase content, deformation mechanism and mechanical properties.