Achieving improved dynamic mechanical properties in twinning-dominated titanium alloys

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Structural materials with low densities and high-strain-rate properties are of significant importance for the armor applications. Titanium and titanium alloys offer great potential in this regard but typically suffer from localized instability deformation during dynamic loadings. Here, we show that enhanced dynamic mechanical properties are attained in a twinning-dominated titanium alloy Ti-15Mo during split Hopkinson pressure bar tests. Under these tests, the solution treated specimens exhibit superior strain hardening capabilities compared to those of the solution treated plus aging specimens. Benefiting from this, the formation of the adiabatic shear bands (ASBs) and the subsequent material failure are delayed. The deformation-producing heat calculation suggests that the temperature rise is not a major origin of the adiabatic shearing. Yet, the strain localization associated with the non-uniform plastic deformation accounts for more. Microstructural characterizations indicate that the {332}<113> twinning, acting as a predominant deformation mode, improves the strain hardening capabilities of the Ti-15Mo alloy. With the increased strain rate, the increasing trend of the twin density gradually decreases, resulting in the grain boundary separations or even the formation of the ASBs at 4060 /s. The ASB’s shear zone has a density of dynamically recrystallized β grains with maximal hardness but poor strain hardening capability, while the adjacent transition zone experiences a highly localized shear deformation accompanied by the ASB widening. On the basis of these results, the impacts of the twinning on the microstructures and mechanical properties of the Ti-15Mo/Ti-15Mo laminated target plates after penetration experiments are discussed. We believe that titanium alloys with distinguished twinning effect can inspire their widespread applications in military fields.