PSI - Issue 83

E.N.T. Isidro et al. / Procedia Structural Integrity 83 (2026) 171–178

177

3.3. Hardness The hardness results presented refer to the polished surfaces. The choice to analyse only polished surfaces is to eliminate the direct influence of roughness and sweep marks, thus evaluating the intrinsic response of the material. Table 6 summarises the Vickers hardness values after the sanding process, evaluating both the top and the side face of each cube.

Table 6. Vickers hardness results in the top and side surfaces of the as manufactured specimens.

Cube

Strategy

VED (J/mm 3 )

Hardness [ HV ] Top surface Side surface 383.8 ± 15.8 347.5 ± 21.1 361 ± 5.1 321.5 ± 31.0 295.8 ± 6.7 273.8 ± 21.1 174.3 ± 9.2 135.0 ± 5.4 146.0 ± 21.6 114.0 ± 4.5 373.5 ± 8.8 297.8 ± 10.0 353.5 ± 15.4 229.0 ± 8.9 222.3 ± 16.6 230.5 ± 25.7 128.8 ± 21.5 163.5 ± 16.6 122.0 ± 4.1 116.8 ± 3.9

1 2 3 4 5 6 7 8 9

96.0 60.0 40.0 26.7 20.0 96.0 60.0 40.0 26.7 20.0

Chessboard

Stripes

10

Hardness varies significantly with the energy used in the additive manufacturing process. Samples produced with high VED, for example 96 J/mm³, exhibited relatively high hardness, typically around 340-370 HV. As the VED decreases, a sharp drop in hardness is recorded. With VED=26.7 J/mm³, the hardness decreased to 190-250 HV, and in samples with only 20 J/mm³ to 200-220 HV. This trend indicates a strong correlation between the supplied volumetric energy and the microstructural quality/density of the sample. As illustrated in Figure 7, the chessboard strategy produces slightly higher and more homogeneous hardness values, compared to the stripes sweeping strategy. Quantitatively, the hardnesses measured in the as-printed state ranged from 300-400 HV under optimal conditions, with a maximum value of 426 HV, which corresponds to about 43 HRC.

120 160 200 240 280 320 360 400

Top surface Side surface

Hardness [HV]

0 40 80

Chess Stripes Chess Stripes Chess Stripes Chess Stripes Chess Stripes 96 96 60 60 40 40 26.7 26.7 20 20

Sweeping strategy / VED [J/mm 3 ]

Figure 7. Relationship between the Vickers hardness of the samples as manufactured with VED and the strategy used in their production. Seria conveniente modificar o gráfico: escala, disposição e cores para ficar diferente do gráfico do artigo completo