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 alpha (alpha eq) and beta 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 alpha eq 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 alpha eq phase contents. In sample with high alpha eq phase content, alpha eq phase is deformed by slip prior to beta phase, and with the increase of strain, beta phase can coordinate deformation by slip initiation and exhibits a better ability to coordinate plastic deformation. In samples with medium alpha eq phase content, the stability of beta phase decreases, slip in alpha eq grain and SIM in beta grain can be initiated simultaneously. However, the formation of SIM would harden beta phase, and with the increase of strain, it would restrain the ability of beta phase to further coordinate plastic deformation. In samples with low alpha eq phase content, the stability of beta phase decreases sharply, which could induce the precipitation of fine-lamellar secondary alpha (alpha s) and acicular martensite alpha'' in beta grain during annealing. These precipitated alpha s and alpha'' can not only inhibit the formation of SIM, but also dramatically reduce the ability of beta phase to coordinate plastic deformation. Meanwhile, the evolution of deformation mechanism in different samples can significantly influence the crack nucleation location (slip band or alpha eq/beta interface) during deformation. This paper analyzes in detail the effect of alpha eq 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.