PSI - Issue 53

João Alves et al. / Procedia Structural Integrity 53 (2024) 236–245 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3.4. Defect analysis Data acquisition was carried out using Brucker's SKYSCAN2214 nanotomograph . A FlatPanel camera was used, with a voltage of 130 kV, a current intensity of 66 μA , and a Cu filter. The resolution was 3.37 μm, with an exposure of 3200 ms and 360° rotation with a 0.4° step. The images were processed using the NRecon reconstruction, CTvox visualization, and CTAn analysis software, also supplied by Brucker. 4. Results and discussion 4.1. Experimental results After data treatment from the tensile test, the nominal and true stress-strain curves were obtained, represented in Fig.5, which describe the behaviour of the Ti-6Al-4V alloy.

Fig. 5. (a) Nominal stress-strain curve of Ti-6Al-4V; (b) True stress-strain curve of Ti-6Al-4V.

Table 5 shows the mechanical properties that were obtained through the study. The results were consistent with what has been observed in the literature (Ghosh et al., 2022), (Gong et al., 2015), (Liu et al., 2020), (Sun et al., 2022). Although the elongation obtained was more extensive than what is usual. When comparing the mechanical properties of Ti-6Al-4V produced by SLM with the ones expected from the traditional methods such as melting, casting, and powder metallurgy, it has been noticed better overall properties, which is promising for this new technology to thrive in this centenary industry (Froes F., 2015). Additionally, microhardness presented a lower value than what is often described in the literature. Having a numerical number value according to ASTM E386-22 (2022) of 339.9 −2 , +2 120 , 419 HV0.5, this indicates lower cooling rates, which might represent a less fragile microstructure and, as a consequence, the possible cause for the extensive elongation obtained in the results (Cao et al., 2017), (Yin & Li, 2022), ( Karimi et al., 2023), (Sun et al., 2022). Concerning its plastic behaviour, it has been noticed a low strain hardening, typically observed in most titanium alloys, as reported by Liu et al. (2020), since the value of the strain hardening exponent, shown in Table 6, is very close to 0, revealing a near perfect plastic behaviour (Moura Branco C., 2011), which lead to a minimal difference between yield strength and ultimate tensile strength. On the other hand, the strength coefficient, also presented in table 6, represents the true strength (σ’) when true strains (ε’) equals 1.