## 1 Introduction  
Additive manufacturing (AM) technologies are becoming widespread thanks to their promising ability to manufacture nearly any complex shape. The metal additive technologies are extremely attractive, being able to produce structural components, made of the typical metal alloys used in industrial applications. There is a large number of AM methods for metal [1], and such methods can be categorized largely into two groups [2]: Directed Energy Deposition and Powder Bed Fusion. The former is characterized by large process complexity and requires a careful design of the part in order to obtain complex shapes with satisfactory accuracy, thus putting the Directed Energy Deposition at a great disadvantage with respect to powder bed methods. Within the latter category, selective laser melting (SLM), also known as direct metal laser sintering (DMLS), deposited by EOS, has the ability to produce highly complex-shaped components with relative ease. It is used in several manufacturing areas, ranging from automotive to biomedical, due to its suitability to manufacture light structures, optimizing the material usage. In such a scenario, a complete understanding of the mechanical performance of SLM-manufactured parts is crucial, due to the not redundant nature of the AM fabricated structures. The titanium alloy Ti6 Al4V is one of the most employed materials in SLM technology and has the following attractive features: high strength, low density, excellent corrosion resistance and biocompatibility [3]. Ti6 Al4V is a commonly studied alloy, and investigations include those looking at microstructure [4; 5], high cycle fatigue [6], static mechanical properties and ductility [7]. Traditional manufacturing processes of Ti6 Al4V rely on forging, casting and rolling of bulk feedstock material, followed by machining to final shape and dimensions. These processes suffer disadvantages, such as poor machinability of Ti6 Al4V, as well as high material waste and energy consumption [8; 9]. These have begun to steer the industry toward SLM technology. Manufacturing with SLM affects the microstructure in a different way, in respect to the traditional manufacturing processes. Because of the high cooling rate, the Ti6 Al4V microstructure mainly consists of fine non-equilibrium hcp martensite \(\alpha\)'-phase. As a result, the tensile strength of the SLM part is higher than that of hot-worked parts, whereas the ductility is lower [10]. In addition, high residual stress usually occurs. A postprocessing heat treatment can increase ductility through the transformation of the metastable martensite into a biphasic \(\alpha\)-\(\beta\) matrix, resulting in a reduction in strength [11]. Researchers have made great efforts in balancing strength and ductility within SLM fabrication of Ti6 Al4V. In [12], the ductility was improved by increasing the baseplate temperature at 570 \({}^{\circ}\)C, resulting in less residual stress. In [13], a double-scanning at a high energy density was employed to obtain fine lamellar \(\alpha\)+\(\beta\) microstructure. Although the obtained material performances resulted in improved mechanical behavior, these strategies are not suitable for industrial production because of their lower process efficiency. Hence, the balancing between strength and ductility is to be achieved by subsequent thermal treatment. Depending upon the final requirements, the SLM parts are usually subjected to Hot Isostatic Pressing (HIP) and/or heat-treatment operation [14]. The HIP reduces the risk of undesirable porosity and breaks down columnar prior-\(\beta\) grains parallel to the stratification direction, giving a more homogeneous behavior. Recently, most of the efforts aiming to select the best processing parameter set focused on the relative density and isotropy improving. The Ti6 Al4V relative density was improved to 99.99% [15]. Aging thermal treatments are currently the most diffused ways to balance strength and ductility: In [16] and [17], specific heat treatments for SLM Ti6 Al4V are mentioned.