Effect of Microstructure, Deformation Mode and Rate on Mechanical Behaviour of Electron-Beam Melted Ti–6Al–4V and Ti–1.5Al–6.8Mo–4.5Fe Alloys

Abstract

Two commercial cost-efficient titanium alloys — a low-alloyed α+β-Ti–6Al–4V (mass.%) and a metastable β-alloy Ti–1.5Al–6.8Mo–4.5Fe melted with a single electron-beam cold hearth melting approach — are employed in a present study as program materials. The influence of microstructure formed by means of the subsequent thermomechanical and heat treatments on both the mechanical behaviour (evaluated by the deformation energy, UD) when tested using standard methods with different deformation rates and the ballistic resistance of plate materials is investigated. As revealed, the weakest dependence of UD on the strain rate corresponds to Ti–6Al–4V alloy with microstructure morphology close to globular one, whereas in the same alloy with a lamellar microstructure (annealed in a single-phase β-field) as well as in Ti–1.5Al–6.8Mo–4.5Fe alloy with various microstructures, UD values significantly depend on the rate of deformation. Moreover, only after annealing at a temperature of the two-phase α+β field, the UD value for Ti–6Al–4V upon three-point flexure at varying deformation rate is equal to the sum of the corresponding values obtained under tension and compression. During subsequent ballistic tests of plates of different thicknesses, it is established that the best ballistic impact resistance corresponds to the materials with higher UD values and lower strain-rate sensitivity. The damage of alloys during all types of testing is discussed in detail in terms of possible mechanisms of deformation and fracture.

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