# Fracture Toughness of Hybrid Components with Selective Laser Melting 18 Ni300 Steel Parts
## 1 Introduction  
Selective Laser Melting (SLM) refers to layer material addition techniques that allow the generation of complex 3D-printed parts by selectively joining successive layers of powder material on top of each other, using thermal energy supplied by a focused, computer-controlled laser beam. This technology is a very high-energy process, as each layer of metal powder must be heated above the melting point of the metal [1; 2]. Moreover, this additive manufacturing process can provide for complex geometry components, repair defects (as an alternative to laser welding [3]) and reconstruction in the moulds industry. The SLM process is largely affected by parameters such as laser power, scan speed rate, protective atmosphere, material used in the process and materials to joint, among others. The wrong choice of these parameters can lead to a high porosity, bad adhesion between layers and a materials interface which can decrease its mechanical behavior. The literature reports an abundance of recent research about the morphologic and mechanical properties of SLM steels. [PERSON] et al. [4] studied the microstructure and mechanical properties of SLM 18 Ni-300 steel and observed that a higher layer thickness and/or scan speed causes a decrease in density. A cellular-dendritic growth mechanism in the solidification was observed where intercellularspacing is less than 1 \(\upmu\)m which leads to an excellent strength and hardness in both as-produced and age hardened conditions. [PERSON] et al. [5] realized an experimental investigation and statistical optimization of the SLM process in 18 Ni300 managing steel, where the correlation between the mechanical and density was positive, and the surface roughness decreases with the energy density. [PERSON] et al. [6] studied the influence of parameters on SLM process and mechanical properties evolution of maraging steel 300. Like previous authors, they prove the considerable influence of the scan rate, laser power and scan spacing as regards the density of a part. Low power laser and high scan rate lead to a low density produced part and high power laser and slow scan rate can achieve 99% of density in a produced part. [PERSON] et al. [7] also obtained 99.9% of relative density in cubic samples produced by SLM using gas atomized H11 grade steel powder. The presence of defects and microstructural heterogeneities creates uncertainty in mechanical properties of SLM produced parts, which complexify their generalized use [8]. Moreover, high SLM mechanical properties are required for structural materials applications. As is often reported in the literature, SLM process affects the material properties due to residual stresses, defects or inherent roughness of the surface [5; 9; 10; 11]. The authors of Reference [12] studied the mechanical behavior of selective laser melting 18 Ni300 steel specimens, concluding that a very high scan rate (400 or 600 mm/s) causes a high percentage of porosity and a consequent drastic reduction of the tensile strength, stiffness and elongation at failure, compared with the results obtained for a 200 mm/s scan rate. The fatigue crack propagation path occurred predominantly in a transgranular direction, crossing the laser layer. The growing direction and grain aspect ratio can lead to anisotropic behavior of SLM parts. The loading direction, in respect to layer deposition plane and grain aspect ratio, plays an important role in its mechanical properties. The effect of building orientation on tensile properties and fatigue crack growth was studied by [PERSON] et al. [13] and observed a lack of anisotropy for selective laser melting 18 Ni300 steel. Strong intra-layer bonding and the absence of dominant texture were the reasons ascribed to this behavior. The same authors concluded that mechanical characteristics of aged SLM are broadly similar to those reported for the aged maraging steel of the same grade. On the other hand, [PERSON] et al.