Spall strength of titanium alloys

A series of high-velocity impact tests of impactors and targets of varying acoustic impedance, including Al - Ti, steel - Ti and Ti - Ti combinations, reveals a β↔ω to phase transition in α + β Ti alloys under shock loading. The presence of the to-phase is confirmed by X-ray diffraction analysis of Ti-4.5Al-3Mo- IV alloy specimens loaded with an impactor at different impact velocities. The experiments show that at an impact velocity greater than ∼ 500 m/s, spall fracture occurs earlier than the ω→x reverse transition (where x is the α-phase, or the β-phase, or their mixture) takes place during the decay of the compression pulse. Hence, the spall fracture in the material develops in the presence of the ω-phase whose dynamic strength is much smaller than that of the β-phase. For the spall occurring after the to ω→x reverse transition, the spall strength of the alloy increases by 25%.