Dynamic deformation behavior and ballistic impact properties of Ti-6Al-4V alloy having equiaxed and bimodal microstructu
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I. INTRODUCTION
COMBAT vehicles such as tanks and armored vehicles are required to have excellent protective capabilities as well as mobility, transportability, maneuverability, maintenance, and corrosion resistance so that the safety of those on board and the survival of the vehicles may be ensured. To this end, intensive efforts are to be made to design armor structures and to modify armor materials used for combat vehicles. In addition, the weight, which is a critical factor in performance improvement and in escalating threats against penetration, should be seriously considered. Since the increased weight decreases mobility and the decreased mobility can negatively affect transportability, passing capability over a buoyed bridge, and maneuverability, engines, and driving devices should be improved. As titanium alloys are light and excellent in corrosion resistance, specific strength, and fracture toughness, they are widely used for airplanes and military purposes, together with recent applications for armor materials of combat vehicles, which require mobility, transportability, and excellent ballistic performance.[1–5] Titanium alloys have higher mass efficiency against multihit ballistic capability as well as against wide-range ballistic capability than rolled homogeneous armors (RHA) and high-strength aluminum alloys, and additional applique armors are not needed.[4,5] Another advantage of tita-
DONG-GEUN LEE, Postdoctoral Research Associate, and YOU HWAN LEE, Research Assistant, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea. SUNGHAK LEE and CHONG SOO LEE, Professors, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, are jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology. Contact e-mail: [email protected] SUN-MOO HUR, Principal Researcher, is with the Agency for Defense Development, Daejeon, 305-600 Korea. Manuscript submitted July 3, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
nium alloys is the low repair and maintenance cost because of their high specific strength and excellent corrosion resistance. In general, armor materials are under dynamic loading such as high-speed compressive or torsional loading and ballistic impact, instead of quasi-static loading. In this case, adiabatic shear bands are often formed as the plastic flow is localized before the thermal energy arising from impact is emitted.[6–13] In an area in contact with a projectile during ballistic impact, momentary melting and chemical reactions such as hightemperature oxidation by high friction heat occur. Around the perforated area, adiabatic shear bands are also formed in the process of thermal-mechanical instability accompanied with serious plastic flow and temperature rise, and cracks occasionally initiate and propagate along the adiabatic shear bands. It is known that fracture by ballistic impact takes place with many phenomena occurring complexly in an
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