PSI - Issue 76

Xabat Orue et al. / Procedia Structural Integrity 76 (2026) 3–10 5 Where ∆ ℎ (∆ , ) is calculated as follows considering the crack extension Δ a , and a dimensional characteristic of the microstructure l R , as well as the effective crack growth threshold stress intensity factor range ∆ ℎ, [8]: ∆ ℎ (∆ , )=∆ ℎ, +(∆ ℎ, −∆ ℎ, ) · (1− −Δ / ) (9) Fig. 1 presents a schematic illustration of the original Kitagawa – Takahashi diagram, along with the modifications proposed by El-Haddad, Murakami and Chapetti, which serve as the foundational framework for the assessment of K T diagram conducted in this study for Ti-6Al-4V manufactured by DED-LB/CW. Thereby, a safe fatigue assessment is ensured if the equivalent defect size a and the corresponding applied stress range Δσ is below the curves.

log Δσ w

log a

Fig. 1. Schematic illustration of K-T diagram with the modifications by El Haddad, Murakami and Chapetti.

Many authors analyzed the mechanical properties of Ti-6Al-4V obtained by DED-LB/W in different conditions [9 – 11], but very few focused on the interaction between the defects and the microstructure [12,13]. To fill this gap, this work presents the assessment of K-T diagram considering the interaction between defects and microstructure by modified models. For this purpose, microstructural analysis and mechanical characterization with Vickers hardness, tensile, HCF and FCG tests were carried out. 2. Material and Method In this study a 1.20 mm diameter Ti-6Al-6V wire was coaxially deposited with a laser beam in commercially pure titanium (grade 2) plates of dimensions 200 x 200 x 20 mm 3 (substrate). Table 1 shows the chemical composition of the wire used: Table 1. Chemical composition of the Ti-6Al-4V wire. Elem. Al V O Fe C N H Ti Comp. (wt.%) 6.75 4.50 0.20 0.30 0.08 0.05 0.01 Bal. To obtain a variation in the resultant microstructure and defects, the samples were extracted from three batches manufactured in two different DED-LB/CW systems. All of them were manufactured with a set of optimized parameters following a zero-defect philosophy [2]. As a result, Lack of Fusion (LoF) defects were avoided and only shrinkage and keyhole pores were detected in fractographic analysis (see section 3). The selected configuration is shown below: Table 2. DED-LB/CW process parameter configuration. Parameter: P L [W] v w [mm/s] v f [mm/s] d o [mm] h L [mm] Value: 2056.10 25 20 1.80 0.75 Where, P L is the real laser power; v w is the wire feed rate; v f is the forward speed; d o is the overlapping distance; h L is the layer height.