PSI - Issue 79

Daniela Neves et al. / Procedia Structural Integrity 79 (2026) 266–274

269

Fig. 3 - Schematic representation of different layers: (a) typical distribution of up-skin, in-skin, and down-skin regions, as well as supports; (b) cross-sectional view illustrating the relationship between the core zone and the in-skin.

1.2. Defects Despite the several advantages associated with the SLM process, defects such as porosity, surface roughness, and residual stresses are commonly observed. These defects can adversely affect the component's fatigue behaviour, as material discontinuities lead to localised stress concentrations that may promote the initiation of fatigue cracks. (Wycisk et al., 2014). The porosities found in SLM components can result from entrapped air, the use of porous powders, lack of fusion (LOF), or the presence of unmelted powder particles between layers. Under fatigue loading, pores tend to grow perpendicular to the build direction, compromising the structural integrity of the components. This issue, which induces anisotropic behaviour in the material, can be substantially reduced by Hot Isostatic Pressing (HIP) (Singla et al., 2021). On the other hand, the surface roughness inherent to the SLM process, which is particularly difficult to reduce in components with complex geometries, can lead to a decrease of more than 50% in the fatigue strength limit (Monaheng et al., 2023). The surface roughness of components produced by SLM depends on the overlap area of the melted zones. Assuming equal hatch spacing, increasing the laser scanning speed reduces the melt pool size, thereby decreasing the overlap between adjacent scan tracks and, consequently, degrading the surface finish (Singla et al., 2021). 2. Material and Experimental Procedure The material used in this experiment was a titanium alloy powder, specifically Ti-6Al-4V. The powder was spherical, with particle sizes ranging from 15 to 45 µm. Its physical characteristics and its chemical composition are shown in Tables 1 and 2, respectively. A total of three batches of specimens were produced using Selective Laser Melting (SLM), with a TruPrint system by TRUMPF. Fig. 4 shows the geometry of the specimens fabricated. The first batch was produced using only virgin powder; the second, with 23% powder sieved twice; and the third, with 23% powder sieved three times.

Table 1. Particle characteristics of Ti-6Al-4V grade 23 D10 [µm] D10 [µm] D10 [µm]

Apparent Density [g/cm 3 ]

Flow Rate

20

34

44

2.49

28