Effect Of Microstructures On Dynamic Compression Behavior And Ballistic Impact Property Of Ti-6Al-4V Alloy

Since the application of titanium alloys in the field of armor stuctures has attracted lots of concern, investigations of dynamic response of titanium alloys under dynamic compression and ballistic impact has becoming hot piont all around the world. In this dissertation, the dynamic compression properties and ballistic impact properties of the Ti-6Al-4V alloys having different microstructures were investigated. In detail, the deformation and failure processes of the Ti-6Al-4V alloy under dynamic compression, the failure mode of the Ti-6Al-4V targets impacted by the 12.7 mm AP, were studed via the using of optical microscopic(OM), scanning electron microscopic(SEM) and transmission electron microscope(TEM). The ballistic impact properties of the Ti-6Al-4V alloys having bimodal microstructures, with which the volume fraction of the transformed beta varied in the range of 70-80%, the thickness of the secondary lamellar alpha varied in the range of 0.75-2.41 um, were tested; The ballstic impact properties of the Ti-6Al-4V based armor configurations were also investigated. The conclusions were draw as follows:The method, by which the initiation and propagation of adiabatic shear band observed in the Ti-6Al-4V alloy under dynamic compression can be captured, were established. The effects of microstructures on dynamic response of the Ti-6Al-4V alloys were investigated. It is found that the improved failure strain observed in the equiaxed microstructure was considered to be related to the less possibility of the formation of adiabatic shear band, the lower velocity of the propagation of adiabatic shear band and the lower velocity of the increasing of the adiabatic shear band induced cracks. The lower possibility of the formation of adiabatic shear band and the slower velocity of the propagation of adiabatic shear band as compared to the lamellar microstructure were thought to be responsible for the higher failure strain analyzed in the Ti-6Al-4V alloy having bimodal microstructure.The failure modes of the Ti-6Al-4V targets having different microstructures investigated fall into two main catagaries: the equiaxed and bimodal microstructure showed failure mode of “Cratering + Ductile Hole Formation + Spalling featured by delamination”, whereas the lamellar microstructure showed failure mode of “Cratering + Ductile Hole Formation + Spalling featured by fragmentation”. The improved Anti-Cratering ability(DHV, about 5.95 GPa) and the smaller spallation(depth, about 4 mm; thickness, about 5 mm) of the rear surface of the Ti-6Al-4V alloy having bimodal microstructure were the very reason for the improved ballistic impact property.The microstructural features of the Ti-6Al-4V alloys having bimodal microstructures were precisely controlled via microstructural engineering. The volume fraction of the transformed β of the Ti-6Al-4V alloys having bimodal microstructure was controlled in the range of 70-80%, and the thickness of the lamellar α in the transformed β was controlled in the range of 0.75-2.41 um. The further investigation on the dyanimc compression properties and ballistic impact properties of the Ti-6Al-4V alloys having bimodal microstructures BW-BA showed that, the ballsitc impact property of the bimodal microstructure BW demonstrated impressive protection effectiveness of about 1.56.Effect of target thickness, double-layering, the order of layers and the microstructures of the Ti-6Al-4V alloys on ballistic impact property of the Ti-6Al-4V based armor configurations were investigated. The results showed that the ballsitc impact property of the “Ti/Ti” armor configuration decreased for the reason that the surface showed nearly no shear strength. The ballistic impact property of the “Ti/RHA” armor configuration showed to be increased by about 49% compared to the “RHA/Ti” armor configuration. The results of the ballistic impact properties of the Ti-6Al-4V based armor configuration with the microstructur es of the first layer of the Ti-6Al-4V targets having equiaxed, lamellar and bimodal microstructures demonstrated that, the most effective configuration was with the equiaxed microstructure.