## 1 Introduction  
According to recent studies, environmental awareness has become a topic of huge interest, and is placed on a comparable level to social equity or education [1]. In order to reduce the carbon footprint of many moving vehicles (e.g., airplanes, cars or rockets) new approaches need to be considered. From a materials engineering point of view it is obvious that the field of lightweight construction still has much potential [2]. There are two main routes which can be followed in order to construct lighter parts. One is the redesign of parts using topology optimisation in order to calculate optimal material distribution and ultimately reduce their weight [3]. In order to build these highly complex parts conventional manufacturing methods can often not be used due to their design limitations or non-cost-effective production. Additive manufacturing (AM) methods can overcome many of these limitations due to their layer-by-layer process [4, 5]. Furthermore, the effectivity could be increased by recycling the used powder multiple times, and therefore environmental impact as well as process waste can be minimised. Furthermore, costs for small badges or individual parts (e.g., implants) can be reduced due to the easy adaptability of the AM processes [6, 7, 8]. Using AM processes brings great challenges; one main problem is the appearance of inherent defects during the processes, such as a lack of fusion, non-meltedpowder, swelling or cracks [9]. Other challenges are the high investment costs, the high maintenance work and the residual stresses introduced in the process [6; 7; 8]. The other route to achieve lightweight construction is to substitute the material with a lighter and comparably strong material. Consequently, titanium and titanium alloys have gained increasing relevance [10]. The metastable \(\beta\)-alloy Ti-5 Al-5 Mo-5V-3 Cr (Ti-5553) is used commercially as a material for the landing gear of the Boeing 787 Dreamliner. Ti-5553 shows a good combination between high mechanical strength and fatigue properties. When heat-treating Ti-5553 it can reach a yield strength (YS) of up to 1300 MPa [11] and an ultimate tensile strength (UTS) of 1500 MPa [12]. Other research has shown that by applying different heat treatments the maximum elongation and the overall fatigue properties can be significantly improved [11]. The difference between the metastable \(\beta\)-titanium alloys and the \(\alpha+\beta\) alloys, of which the most widely used is Ti-6 Al4V, is that the matrix and precipitation phases are the other way around [13; 14]. Hence, Ti-5553 shows a bcc \(\beta\)-titanium matrix with good ductility and toughness, and an hcp \(\alpha\)-titanium precipitation. \(\alpha\)-titanium can be precipitated, depending on the respective temperature during the precipitation process, as primary, \(\alpha_{\text{p}}\), or secondary, \(\alpha_{\text{s}}\), alpha. These precipitations act as strengthening phases and can increase, depending on their size, shape and distribution, the mechanical strength significantly [15]. In the case of conventionally and AM-produced Ti-5553, quenching during the manufacturing process or a subsequent heat treatment can lead to the formation of the strength-reducing omega phase [16; 17; 18; 19]. This can be excluded in the present work due to the prevailing process temperatures and the associated slow cooling rate [13; 20]. If these are very fine grains, then they have the greatest influence due to the formation of dislocation barriers at \(\alpha-\beta\) interfaces. If these grow larger, they can further improve the elongation properties due to slip and shear processes in large primary \(\alpha\) precipitations [21; 22]. Furthermore, titanium is also very resistant to corrosion and lightweight [13]. When combining AM with new advanced materials as well as with new approaches, such as topology optimisation, in order to design lightweight parts, a significant amount of weight can be saved without losing any stability and function ability [2; 5].