PSI - Issue 76

Xabat Orue et al. / Procedia Structural Integrity 76 (2026) 3–10

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Fig. 2. Microstructural analysis by OM at 50x (left) and 200x (center), and by SEM at 1500x with SE2 (right). The martensitic microstructure obtained leads to high values of hardness, stiffness and strength, but low ductility (Table 3). This is also in line with the literature [20]. Table 3. Results of Vickers hardness and tensile tests in horizontal direction. HV [kgf/mm 2 ] E [GPa] σ yp [MPa] σ ut [MPa] A t [%] Value: 381,35 ± 8.53 103,45 ± 11,44 997,84 ± 22,37 1096,25 ± 9,16 5,74 ± 1,08 Where, E refers to the Young’s modulus (stiffness), σ yp is the yield strength (stress), σ ut is the ultimate tensile strength (stress) and A t stands for the total percentual elongation (strain). The values correspond to the meansand the standard deviations. Related to the dynamic mechanical performance, S-N curve of HCF tests at R = 0,1 for horizontally extracted samples with no heat treatment (T0) is shown in Fig. 3, where fractures (FR) and run-outs (RO) are distinguished. The fatigue limit range ( Δσ w ) obtained by the up-and-down method according to Dixon [16] is 598,5 MPa and the corresponding knee-point ( N k ) is at 2,18·10 7 cycles.

y = 1640,6x -0,06 R² = 0,6759

FR-T0

RO-T0

Potencial (FR-T0)

1000

800

log Δ σ (MPa)

400

1,00E+04

1,00E+05

1,00E+06

1,00E+07

log N (cycles)

Fig. 3. S-N curve of HCF tests at R = 0,1 of horizontal specimens with no heat treatment. Fractographical analysis of tested samples revealed that all the defects that cause the failure (killer defects) are internal based on the relationship between the size and the position. According to Murakami, a defect is considered internal when the ratio between the equivalent radius of the same area ( R eq ) and the position of its center to the outer surface ( h ) is less than 0,8. In such cases, the geometrical factor Y takes a value of 0,50 [6]. It should be noted that this might be due to the extraction of samples from inside the manufactured solid blocks avoiding the critical zones (see section 2). The defect distribution inside the blocks manufactured by DED-LB/CW is usually very low and homogeneous [2].