PSI - Issue 66

Nur Mohamed Dhansay et al. / Procedia Structural Integrity 66 (2024) 87–101 Author name / Structural Integrity Procedia 00 (2025) 000–000

94 8

Stress relief

Bi ‐ modal

As ‐ built

a)

b) Threshold [MPa √ m] Threshold [MPa √ m]

Fig. 5. Plots of the (a) Δ K th versus R, and (b) Δ K th versus K max for all three conditions and orientations

With regards to the bi-modal microstructure fracture behaviour in Fig. 7, transgranular quasi-cleavage faceted fracture is also observed but with larger facets than the AF and SR conditions due to larger grain sizes. Overall, from the fracture surface and crack path, it is observed that the DA condition has larger crack deflections, crack branching/bifurcation and fracture roughness than the AF and SR counterparts. However, the observation in AF and SR conditions where laths orientated at ± 45° influence the crack path is not observed or at least not as obvious in the DA condition. Due to the specific heat treatment, the PBG has kept its morphology and is somewhat apparent on the fracture surface. However, the difference is that we don’t specifically observe varying levels of roughness contained within a PBG compared to another PBG roughness level, as was observed in the AF and SR conditions. With the increase in grain size and presence of β phase, the bi-modal condition is more ductile than the LPBF conditions. This is also observed in the non-faceted fracture regions which is more ductile in nature than the AF and SR counterparts. It is also observed that the ZX orientation has larger amounts of faceted fracture than the XZ and XY orientation, as seen in Fig. 7(b). It is likely due to the grain orientation and crack plane in the ZX orientation being more favourable for faceted fracture than the XZ and XY orientation.