PSI - Issue 79

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

272

1 2 3

559 ± 19.9

483 ± 37

498 ± 41.9

3.2. Roughness measurements The results from roughness analysis are presented in Table 6. As the amount of recycled powder increases from Batch 1 to Batch 3, the surfaces exhibit greater roughness and heterogeneity, with Ra showing greater variability and Rt increasing progressively, indicating more pronounced peaks and valleys.

Table 6. Surface roughness parameters (Ra and Rt) for different batches Batch Ra (µm) Rt (µm)

1

7.21 ± 0.81

58.04 ± 12.89

2

8.90 ± 0.43

70.37 ± 7.59

3

8.68 ± 1.72

88.08 ± 14.58

3.3. Microstructure Analysis The microstructural analysis of Ti-6Al-4V specimens manufactured revealed a typical acicular (needle- like) α′ martensitic structure. Across all samples (Fig. 6), porosity and lack-of-fusion defects were identified, generally exhibiting elongated, irregular morphologies. However, Batch 1 exhibited the lowest porosity, consisting mainly of small, predominantly spherical gas pores, suggesting that this batch was manufactured under more stable processing conditions.

Fig. 6 – Microstructures obtained with optical microscopy: a) Batch 1; b) Batch 2; c) Batch 3

3.4. Defect Analysis – Nanotomography Table 7 presents the nanotomography defect analysis for the Ti-6Al-4V samples manufactured under similar conditions, but with different proportions of recycled powders. Batch 3 exhibits a higher fraction (2.52%) compared to Batch 2 (0.82%). In addition, the total surface area of the defects in Batch 3 (2134.84 mm²) is higher than that in Batch 2 (310.64 mm²), indicating a greater number of irregular, interconnected pores. Although the total sample volume differs only slightly between the two batches, the significant increase in both defect volume and surface area in Batch 3 indicates reduced process stability associated with the additional powder recycling cycle.