Role of Microstructure on the Shock-Induced Strengthening Behavior of Ti–6Al–4V Alloy

The influence of microstructure on the shock-induced strengthening behavior of Ti–6Al–4V (Ti-64) alloy was systematically investigated through plate impact experiments and quasi-static reload compression tests. Ti-64 displays no enhanced shock-induced strengthening effect at equivalent strain, regardless of the microstructure and shock stress amplitude. However, the shock-induced enhancement ratio is higher in the alloy having the bimodal microstructure with high equiaxed primary α-phase (\(\alpha_{P}\)) volume fraction or the lamellar microstructure with wide α-platelets. The microstructure analyses show that the substructures of the postshock Ti-64 with both bimodal and lamellar microstructures are dominated by planar slip. Dislocations are easier to nucleate, move and tangle in those large-sized α phases, such as equiaxed \(\alpha_{P}\) and wide α-platelet, leading to the formation of reticular substructures and slip bands. However, the dislocation density is relatively low in the small α plate of the transformed β regions and in the narrow α-platelet, which is attributed to the relaxation of shock stress and consequently to the suppression of dislocation nucleation caused by the obvious grain/phase boundary damping effect. Only a small number of twins were formed in the lamellar microstructure with wide α-platelet, indicating that grain size and interface damping also affect the twinning behavior of Ti-64 under shock loading conditions.