PSI - Issue 83

Daniele Cortis et al. / Procedia Structural Integrity 83 (2026) 3–13

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3. Results and discussion 3.1. Tensile properties

The evaluation of E and ν has been done considering a minimum of fifty different discrete measured values in the evaluation range (i.e., lower and upper limits 10% and 40% of YS). As prescribed by the EN ISO 6892-1 standard, data were validated assuming a correlation coefficient > 0.9995. Tests were repeated three times without exceeding the 50% of the YS. The estimation of uncertainty was done, according to the Annex K of the above standard, by repeated measurements considering a 95% confidence level. Since the average values of E and ν were known, it was possible to calculate, by means equation 3, the Shear Modulus (G). The stress-strain curves, expressed in terms of true stress ( σ ∗ ) and true-strain ( ε ∗ ), equations 4 and 5, are plotted in Fig. 5, while numerical data are summarized in Table 4. ܩ ൌെ 2 ήሺ1൅ ߥ ሻ ሺ3ሻ Table 4. Average tensile test results at different temperatures (confidence level 95%). Temperature (°C) YS (MPa) UTS (MPa) A (%) E (GPa) ν G (GPa) -100 435.3 ± 4.7 521.5 ± 8.6 9.7 ± 1.4 68.0 ± 0.07 0.319 ± 0.010 25.8 +22 (room temperature) 414.3 ± 3.7 491.7 ± 11.2 9.4 ± 1.7 63.7 ± 0.01 0.338 ± 0.002 23.8 +100 370.0 ± 2.4 415.1 ± 2.0 15.6 ± 1.0 61.8 ± 0.03 0.351 ± 0.001 22.9 +200 183.7 ± 8.0 191.4 ± 1.1 10.1 ± 2.5 45.8 ± 0.09 0.396 ± 0.007 16.4 ∗ ൌ ln ሺ1 ൅ ሻ ሺ4ሻ ∗ ൌ ɐ ሺ1 ൅ ሻ ሺ5ሻ At room temperature (+22 °C), the plot of Fig. 5 (a) reveals the well-known “ Portevin–Le Chatelier ” (PLC) effect [Zhang et al. (2022)], which refers to the repeated propagation of localized deformation bands on the surface of test pieces during plastic deformation. PLC is a result of interaction between solute atoms and mobile dislocations generated by the Dynamic Strain Aging (DSA). DSA happens when the diffusion of the solute atoms is comparable to that of dislocations at given temperature and strain rate. These atoms pin dislocations, increasing the stress required for the plastic deformation flow. The diffusion mechanism is related to several factors like temperature, strain rate, available solute atoms and the dislocations density [Bakare et al. (2021)]. The plastic deformation instabilities are commonly observed as repeated irregularities on the stress-strain curve. The plot of Fig. 5 (a) highlights the so-called Type A serration mode characterized by a periodic and quasi-continuous gradual rise of the stress followed by a drop to or below the mean. Usually, the PLC effect can be observed in alloys with a negative strain rate sensitivity (i.e., material strength decreases with increasing of strain rate). The addition of elements, such as Sc and Zr, helps to reduce the intensity of PLC and leads to the appearance of predominantly Type A serration, decreasing the intensity of stress drops during the plastic deformation [Bakare et al. (2021)]. Despite of PLC effect, the mechanical properties at room temperature are quite well in agreement with the material specifications [StrengthAl (2025)]. The YS is ≃ 415 MPa, UTS ≃ 490 MPa and the A ≃ 9.5%, slightly below the expected range (i.e., 12-17%). Hence, data confirm the setup of the PBF-LB process parameter and the high relative density reached (> 99%), as well as the efficacy of the aging heat treatment. At low temperature (-100 °C) the limited diffusion prevents solute atoms from segregating at dislocations, suppressing the DSA and thus the PLC effect, see Fig. 5 (b). However, a closer examination of the stress-strain curves