A comparative study on dynamic deformation and ballistic impact response of Ti–4Al–2.5V–1.5Fe–0.25O and Ti–6Al–4V alloys

Titanium alloys are most suitable for lightweight armour applications due to their superior strength to weight ratio, and α+β Ti alloy Ti–6Al–4V is widely used in armour applications. One of the critical factors limiting the widespread use of Ti alloys in armour application is their high cost. Recently, Allegheny Technologies Incorporated introduced ATI-425® Ti alloy with the chemical composition of Ti–4Al-2.5V-1.5Fe-0.25O as a low-cost alternative to Ti–6Al–4V. Though ATI-425 Ti alloy is primarily intended for armour applications, only limited ballistic results are available in the open literature. In the present work, we compare the quasi-static, dynamic deformation, ballistic impact response and post-deformation microstructure of a low-cost α+β Ti alloy ATI-425 with that of Ti–6Al–4V alloy. Analysis of the results showed that both alloys showed similar yield strength values during quasi-static tension and compression tests, while ATI-425 Ti alloy showed higher tensile ductility, Charpy-V notch impact energy and dynamic flow stress than Ti-6Al-4V. The ATI-425 Ti alloy also exhibited slightly better ballistic performance measured in terms of V50 ballistic limit velocity. Detailed microstructural analysis on quasi-static and dynamic compression-tested samples showed mainly {101–2} tensile twins, whereas {101–2} and {112–1} tensile twins are observed in ballistic-tested samples of both the alloys. Activation of deformation twinning in ATI-425 Ti alloy with higher oxygen is attributed to lower Al content which enhances the twinning activity. Adiabatic shear band (ASB)-induced plugging mechanism is ascertained as the perforation mode in both alloys during the ballistic impact. Analysis of propensity to ASB formation indicated that Ti-6Al-4V has a slightly better resistance to ASB formation than ATI-425 Ti alloy. The improved ballistic performance of ATI-425 Ti alloy in comparison to Ti-6Al-4V is attributed to the higher dynamic flow stress, Charpy-V notch impact energy absorption, and moderate resistance to adiabatic shear band formation.