Phase Composition Effects on Dynamic Behavior and Strain Rate Sensitivity in Metastable β-Ti Alloys

Abstract

In this study, high strain rate tension tests are conducted to determine and compare the dynamic mechanical behaviors and deformation mechanisms of different phase composition α-β metastable β-Ti alloys using a split Hopkinson tension bar. Two typical bimodal equiaxed αp + β and lamellar αs + β Ti-45551 alloy microstructures are formed through different hot working and thermal processing for investigating the effect of phase composition or microstructure on mechanical properties and strain rate sensitivity. It is demonstrated that dislocation nucleation and motion in the α/β phase and dislocation tangle or pile up at the α/β interface are typical deformation modes in both of the typical dual-phase Ti alloys at quasi-static loading conditions. Under dynamic loading, both the strength and ductility show a clearly positive strain rate dependence, which is directly related to dislocation activation in the α + β Ti-45551 alloy. Based on microstructure characterizations, it is shown that deformation twinning starts to become a major deformation mechanism in equiaxed αp + β microstructures under dynamic loading conditions. However, deformation twins are not favored in the lamellar αs + β Ti-45551 alloy due to its nano phase size. Finally, the mechanical behaviors and strain rate sensitivity are strongly dependent on the phase composition of metastable β-Ti alloys.

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“…There are several past studies corroborating that the concentration or confinement of defects, such as dislocations at the α s lamellae and αs/β interface, dictates the deformation modes and/or mechanical behaviors of a dual-phase (α + β) Ti-based alloy. For example, using TEM observations, Wang et al [ 59 ] revealed the presence of a high-dislocation-density structure in the αs lamellae and αs/β interface. On the other hand, the dislocation density in the α p phase was very low due to its limited slip systems at room temperature.…”

“…On the other hand, the dislocation density in the α p phase was very low due to its limited slip systems at room temperature. Due to this, they affirmed that the dislocations impeded by the α phase increased the strength of dual-phase-45,551 alloys [ 59 , 60 ]. On the other hand, in Table 3 , it can also be noticed that the elongation to fracture and elastic modulus have quite the opposite tendency concerning mechanical strength.…”