PSI - Issue 82

Tomáš Babinský et al. / Procedia Structural Integrity 82 (2026) 162–168 Tomáš Babinský et al. / Structural Integrity Procedia 00 (2026) 000–000

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Fig. 1. Drawings of the (a) tensile and (b) fatigue testing specimens. Sketch (c) illustrates vertical and horizontal specimen orientations.

2.2. Mechanical testing Tensile tests were performed in laboratory air at room temperature using the flat dogbone specimens with the dimensions as shown in Fig. 1a. Tensile tests were conducted in displacement control with a constant rate of 16.7 μm/s using a screw-driven testing machine Zwick Z50. Axial strain was measured using a clip-on extensometer by Zwick. Analysis of the results complied with standard ISO 6892-1 (2019). At least 3 specimens were tested per batch. Low-cycle fatigue tests were performed in compliance with standard ISO 12106 (2017) in laboratory air at room temperature using the machined cylindrical specimens with the dimensions as shown in Fig. 1b. Fully-reversed (R ε = -1) uniaxial tests were conducted in total strain amplitude control within the range 0.35–1% and constant strain rate of 2×10 -3 s -1 using a servohydraulic testing machine MTS 810. The strain amplitudes were chosen with regard to estimated low-cycle fatigue life falling within 100–100000 cycles. Axial strain was measured using an MTS contact extensometer with alumina rod extensions attached to the specimen gauge. At least 400 data points were recorded in each cycle for the subsequent data analysis. Fatigue life was evaluated using the criterion !" = # ! # " ≤−0.3 (1) where σ m stands for mean stress and σ a stands for stress amplitude in the respective cycle. 2.3. Microstructural characterization Initial microstructural state has been characterized from the metallographic sections prepared from the supplied rectangular blocks by standard metallographic procedure consisting of cutting of the specimens parallel and transversal to the building direction, grinding down to P4000 with SiC paper, polishing down to 1 μm with a diamond paste, and electropolishing. Mirror-like surface was achieved by electropolishing at -15 °C/54 V/6 s using an electrolyte consisting of a solution of ethanol, nitric acid and perchloric acid with volume ratio 93.9:1.4:4.7. In some cases, meltpool features were highlighted by electropolishing at 24 °C/2 V/2×5 s using an electrolyte consisting of a 10% solution of oxalic acid. Thin foils for detailed observations using a transmission electron microscope (TEM) were prepared from thin plates using electropolishing in a double jet device TenuPol2. Electropolishing was performed at -5 °C/11 V using an electrolyte consisting of a solution of methanol, glycerol and perchloric acid with a volume ratio of 7:2:1. Microstructural characterization has been conducted by means of electron microscopy, using scanning electron microscopes (SEM) Tescan LYRA 3 XMU FEG/SEMxFIB and Thermo Scientific Apreo ChemiSEM, and TEM