## 1 Introduction
The inertia introduced in aircraft creates a critical design consideration for the structures [13]. Foreign object damage (FOD) to fan blades of aircraft engine and the fan-blade out (FBO) events have also been identified as main factors affecting safety in the operation of jet engines [14; 15]. Fan blades are susceptible to impact from hard objects like stones and gravel and studies have shown that the damage related to FOD occurs in the form of cracks in damaged zones and dynamic deformation of blades [14; 16]. Loss or detachment of blades or parts of the blades when the engine is running includes all the nonlinearities of structural dynamics such as high strain rate plastic deformation of materials and dynamic interaction between turbo-engine structural components [15]. The preceding discussion suggests the need to develop knowledge on the high strain rate deformation properties of additively manufactured Ti6 Al4V(ELI). Such a pool of knowledge will provide the aircraft industry with a strong basis of testing the suitability of such AM material for bearing different types of mechanical loads. The strength and failure of materials are not entirely dependent on the properties of materials, but are rather strongly influenced by stress state, strain rate and temperatures. The strain rate and temperatures strongly influence the dislocation mechanics of a material. High strain rate causes instantaneous strain hardening, thus increasing the yield strength, whereas increasing temperature increases the activities of dislocations and provides sufficient activation energy for the annihilation of dislocations, thus decreasing flow stress [17; 18]. Fundamentally, deformation of materials at intermediate strain rates (>10 s\({}^{-1}\)) and high strain rates (>500 s\({}^{-1}\)) is different from that at quasi-static conditions (<10 s\({}^{-1}\)). At quasi-static conditions, static equilibrium is almost invariably maintained as any element in a material in this state has a summation of forces acting on it tending to zero (the inertia force is very small and can be ignored). However, at dynamic and high strain rates, deformation stresses travel through materials very fast and over small durations, and therefore inertial force is induced. Moreover, dynamic and high strain rates affect thermally activated mechanisms in materials and may results in microstructural changes through adiabatic heating, which make them behave perfectly plastic [19]. More recently, efforts have been made to study the dynamic properties of Ti6 Al4V(ELI) produced by various AM technologies. [PERSON] et al. [20] investigated the thermo-mechanical properties of Ti6 Al4V produced by laser deposition-additive manufacturing technology (LDAM) at a wide range of strain rates and temperatures. The effects of porosity on deformation and fracture behaviour under static and dynamic loading of the Ti6 Al4V produced by laser-engineered-net shaping (LENS) technology was investigated by [PERSON] et al. [21]. The effects of building direction on microstructure, dynamic mechanical properties, and deformation mechanisms of electron beam melted Ti6 Al4V was presented by [PERSON] et al. [22]. [PERSON] et al. [23] investigated the tensile response of dense and porous AM Ti6 Al4V parts under quasi-static and dynamic conditions. Most of these studies have focused on dynamic properties of as-built additive manufactured Ti6 Al4V alloy parts. To the best knowledge of the authors, no work has been done on the effects of various heat treatment strategies on the dynamic mechanical behaviour of DMLS Ti6 Al4V(ELI). The authors' previous work in References [24; 25] focused on the effects of stress relieving heat treatment on high strain rate and impact toughness of direct metal laser sintered (DMLS) Ti6 Al4V(ELI). The aim of this study is to investigate the high strain rate deformation behaviour of various microstructures of DMLS Ti6 Al4V(ELI) formed through different heat treatment strategies.