Dynamic deformation behaviors and high velocity impact characteristics of Ti-6Al-4V alloy have been studied with considering the influence of heat treated microstructures, namely, equiaxed, bimodal and lamella. Four different heat treatment conditions were employed for the development of the microstructures, and the dynamic material properties on the microstructures were respectively obtained by the analyses of static and dynamic deformation characteristics. The characteristics to the high velocity impact on the microstructures were also investigated by means of experiments and numerical analysis, and the compatibility of the dynamic material properties were validated. The study concluded as follows;

1. The dynamic material properties of Ti-6Al-4V alloys obtained in terms of Johnson-Cook model were showed the differences in values with respect to the type of microstructures. According to the numerical analyses using the properties on microstructures, the properties simulated accurately with 0.5~7.4 % of errors for rod impact experiments and long rod penetration experiments, and so the dynamic properties on microstuctures were required to increase the accuracy of the impact problem analysis including Ti-6Al-4V alloy.

2. For dynamic deformation analysis, Ti-6Al-4V alloy presented the tendency of fracture by ASB(adiabatic shear band) under high strain rates since a shear crack on the lateral surface in the specimen, localized plastic flow and voids at the grain interface were observed as the major failure mechanisms of the material. The lamella microstructure had higher strength than that in the equiaxed microstructure, but the ductility in equiaxed microstructure was superior to that in the lamella microstructure. Bimodal microstructure exhibited intermediate characteristics between equiaxed and lamella microstructures. The strain hardening exponent, n increased with increasing the strain rate for all microstructures and so the strain hardening exponent was strongly dependent on the strain rate. Under the same strain rate, the strain hardening exponent decreased in the order of equiaxed, and bimodal and lamella microstructures due to the change of fraction of primary a phase and the competition between thermal softening and work hardening. On the other hand, the strain at maximum stress decreased slightly with increasing the strain rate in case of the equiaxed and bimodal microstructures, whereas the strain at maximum stress decreased considerably with increasing the strain rate for the lamella microstructure.

3. Rod impact experiments and long rod penetration experiments were conducted to analyze the resistance to high velocity impact on microstructures of Ti-6Al-4V alloy. For the rod impact(Vs = 200 ~250 m/s), the resistance of equiaxed microstructure was higher than that of lamella structure, which is corresponded to the results of dynamic deformation analyses. However, for the long rod penetration(Vs ≒ 1,200 m/s), all microstructures showed the similar penetration depth, and the resistance of lamella microstructure was increased relatively compared to the results of rod impact experiments. It is believed that the results were coming from the hydrodynamic behavior of material at high impact velocity and the difference of penetration mechanism of long rod penetrator with rod erosion.

4. The characteristics to the high velocity impact of Ti-6Al-4V alloy were greatly different between a small caliber bullet and a long rod penetrator since penetration mechanisms are depended on not only the kinds of material but also the types of penetrator. But the dependence of the penetration mechanism on the long rod penetrator associated with the corresponding microstructure were not examined enough to find the influence at high velocity. It is thus believed that the study on the area would be future work to provide fundamental ideas for improving an accuracy of impact analyses with Ti-6Al-4V ally.