# Tensile Properties of As-Built 18 Ni300 Maraging Steel Produced by DED
## 1 Introduction  
Additive manufacturing (AM) is a set of technologies in which three-dimensional components are built on a layer-by-layer basis. One of the possible classifications of metallic AM processes distinguishes powder-bed and non-powder-bed techniques, with directed energy deposition (DED) belonging to the latter. One of the advantages of not requiring the spread of a fresh powder layer at each height increment is the ability to locally repair already existing components, which constitutes one of the most attractive advantages of DED processes when compared to selective laser melting (SLM) or selective laser sintering (SLS). In DED, the metallic feedstock is fed directly into the path of the heat source (which may be a laser or an electron beam) through a powder splitter and nozzle head, both mounted onto a numerically controlled system. The system also relies on an inert gas supply to shield the melting pool of corrosion phenomenon. Although DED processes have better productivity than SLM, the surface quality and geometric fidelity is usually worse, thus requiring subtractive operations such as machining before the component is ready for its intended application. DED techniques have been used to successfully produce claddings and/or fully three-dimensional components with different alloys, such as titanium [1; 2], nickel [3; 4], copper [5] and aluminium [6] alloys, tool steels [7; 8] and stainless steels [9; 10]. One additional material group that has been DED-processed are Maraging steels, which consist of high-strength, precipitation hardened steels. This research work focuses on 18 Ni300, which contains 18% Ni, substantial presence of Co and Mo, as the former promotes age hardening by reducingthe solubility of Mo in the matrix [11], while the latter forms the intermetallic compounds that precipitate, enhancing the alloys' strength [12]. Additionally, small quantities of Ti and Al (0.05-0.5% and 0.05-0.15%, respectively), further contribute to intermetallic phases to be precipitated [12]. These alloys find their applications in military [13; 14], aircraft [15], aerospace [16; 17] and die-casting and tooling industries [18; 19]. Recent research has been focusing on Maraging processing through DED: [PERSON] et al. [20] optimised the process parameters of 18 Ni300 and built processing maps according to five different objectives, with these being dilution proportion, height, width, depth and porosity. [PERSON] et al. [21] optimised the processing parameters of 18 Ni300 on AISI H13, reaching a set of parameters of a laser power of 1850 W, a scanning speed of 12 mm s\({}^{-1}\), feeding rate of 12 g/min, shielding gas flow rate of 25 L/min and carrier gas flow rate of 4 L/min. [PERSON] et al. [22] studied the effect of deposition parameters on single-bead depositions, as well as the residual stresses on a bulk cube, concluding that an energy density of 34.7 mm\({}^{-2}\) yielded a fully dense specimen with relatively low residual stresses. [PERSON] et al. [23] wrote a review article which explores the use of Maraging alloys containing 18% Ni content within metallic additive manufacturing processes. [PERSON] et al. [24] studied the influence of processing parameters of DED-processed 18 Ni300 by testing tensile specimens produced through nine different conditions following an orthogonal Taguchi array, concluding that the optimised set reached a ultimate tensile strength of 959.2 MPa. [PERSON] et al. [25] reported the influence of layer thickness on mechanical properties of heat-treated samples, obtaining ultimate tensile strengths of 1958 MPa in the samples with the lowest tested layer thickness of 0.5 mm. [PERSON] et al. [26] analysed the thermal cycles' influence on previously deposited layers in an 18 Ni300 by varying the inter-layer idle time, thus inducing an in situ aging effect, successfully triggering nano-precipitation of intermetallics that enhanced the sample's hardness and strength. Regarding other martensitic precipitation-hardenable steels, [PERSON] et al.