Electron Beam Cold Hearth Melted Titanium Alloys and the Possibility of Their Use as Anti-Ballistic Materials

Abstract

Three commercial titanium alloys: two-phase α+β Ti-6Al-4V (low alloyed), and T110 (Ti-5.5Al-1.5V-1.5Mo-4Nb-0.5Fe, higher-alloyed), and β-metastable Ti-1.5Al-6.8Mo-4.5Fe were melted using EBCHM approach in the form of 100 mm in diameter ingots with the weight of about 20 kg each. After 3D hot pressing at single β-field temperatures ingots were rolled at temperatures below β-transus onto plates with thickness varying from 3 mm to 25 mm. Different heat treatments, including annealing at α+β or β-field temperatures, and special strengthening Surface Rapid Heat Treatment (SRHT) which after final aging provided special gradient microstructure with a hardened surface layer over ductile basic core, were employed. Mechanical properties were studied with tensile and 3-point flexure tests. It was established that the best combination of tensile strength and ductility in all alloys studied was obtained after SRHT, whereas at 3-point flexure better characteristics were obtained for the materials annealed at temperatures of (α+β)-field. At the same time, ballistic tests made at a certified laboratory with different kinds of ammunition showed essential superiority of plates having upper layers strengthened with SRHT. The effect of microstructure of the alloys, plate thickness and type of used ammunition on ballistic resistance is discussed.

Effect of Strain Rate on Mechanical Behavior and Microstructure Evolution of Ti-Based T110 Alloy

“…This result is somewhat unexpected because the T110 and Ti64 alloys differ each other in many parameters: namely, chemical composition, the ratio of α-and β-phases, and conventional mechanical characteristics. In addition, they also showed different ballistics resistance against different types of ammunition [6,9]. Probably, regardless of the above noted differences, both alloys with a well-formed globular microstructure provide such a combination of strength and plasticity under highstrain rate loading that a somewhat lower strength of Ti64GL is compensated by a slightly higher fracture strain.…”

“…1 This rather conventional processing was described in more details in. [5,9] To study the effect of the degree of the microstructure transformation (formation of as more as possible homogeneous microstructure of globular type with aspect ratio close to 1), the final cross-rolling of pressed semi-product was carried out with different reductions of plate thickness (h) to 15 mm (ε total = 2, including 3D pressing stage, Fig. 1a), and 10 mm (ε total = 3).…”

“…As for all titanium two-phase α+β alloys [5], the microstructure of the T110 alloy is mainly determined by the deformation-force and temperature conditions of thermomechanical treatment. The basics of the influence of the thermomechanical treatment mode on the evolution of the T110 microstructure were considered in [9]. The thermomechanical treatment regimes used in this study in combination with the subsequent annealing allowed to transform the initial coarse-grained lamellar structure (Fig.…”

“…Besides, a good balance of various mechanical properties of the alloy can be obtained after a number of processing routes, which can be employed for critical products, including aerospace and military applications [6][7][8]. For instance, ballistic testing of T110 sheets with the use of various type of live ammunition showed at least 20-25% higher ballistic resistance compared to the commonly used for this purpose Ti-6Al-4V alloy [6,9,10]. However, the dependence of the mechanical properties of the T110 alloy on the various types of processing and the structure-phase state created by them has been studied to a very limited extent, mainly by standard tensile tests.…”