Mechanical Behaviors of Ultrafine-Grained Ti-6Al-4V Alloy During Compression at Various Strain Rates

Ultrafine-grained (UFG) Ti-6Al-4V alloy with average grain sizes of 305, 430, and 669 nm was fabricated by high-energy ball-milling and spark plasma sintering. The mechanical behaviors of consolidated titanium alloy with different grain sizes were studied under uniaxial compression at the quasi-static strain rate of 1 × 10⁻³ s⁻¹ and high strain rates ranging from 0.5 × 10³ to 2.9 × 10³ s⁻¹. Shear bands can be observed in specimens tested under quasi-static and dynamic condition. It is discovered that when the grain size decreases, the flow stress increases and shear band instability takes place at lower strains. The flow stresses of UFG titanium alloy with different grain sizes demonstrate similar dependence on the strain rate when the strain rate ranges from 1 × 10⁻³ to 0.5 × 10³ s⁻¹. However, the strain rate sensitivity m dramatically increases at higher strain rates and is reduced with the decrease of grain size. It is considered that the propensity for adiabatic shear banding \( \chi_{\text{ASB}} \) during dynamic compression is increased with the reduction of grain size because of the improved yield strength as well as the diminished strain rate sensitivity.