PSI - Issue 52

Ivo Šulák et al. / Procedia Structural Integrity 52 (2024) 143–153 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3

The chemical composition of Alloy 400 as determined by an energy dispersive x-ray (EDX) microanalysis is listed in Tab. 1.

Table 1. The chemical composition of Alloy 400 (in wt. %). C Si Mn Al

Fe

Cu

Ni

Bulk

0.1 0.1

0.2 0.2

0.9 1.1

0.1 0.1

1.8 1.6

33.3 31.9

Bal. Bal.

LPBF

Fig. 1. a) The schematic illustration of blocks produced via the LPBF process for creep (left) and fatigue (right) experiments; b) the drawing of creep (left) and fatigue (right) specimens.

2.2. Observation Detailed microstructural investigation and fractographic observation of features specific for fatigue and creep loading of bulk and LPBF Alloy 400 were performed using a Tescan Lyra 3 XMU scanning electron microscope (SEM) equipped with a Symmetry electron backscatter diffraction (EBSD) detector and an Oxford XMax 80 EDX spectrometer. Analysis of the internal dislocation structure of both materials was carried out in a Thermo Scientific™ Talos F200i transmission electron microscope (TEM). TEM foils were prepared by a standard procedure consisting of spark cutting, mechanical polishing, and 3 mm disc cutting. Final electrolytic polishing was carried out at a temperature of - 5 °C and voltage of 20 V in a solution of acetic acid and perchloric acid. 2.3. High-temperature fatigue and creep experiments Stress-controlled high-temperature fatigue experiments were performed on cylindrical specimens with gauge length and diameter of 9 and 3 mm, respectively. A symmetrical push-pull cycling with a loading frequency of 5Hz was done using a servo-hydraulic testing machine MTS 810 equipped with a three-zone resistance furnace. The temperature was monitored and controlled by four K-type thermocouples attached to the surface of the specimens. Experiments were carried out at 400 °C, 550 °C, 650 °C, and 750 °C. The creep tests were performed using self-designed creep machines developed in the IPM in the 1970s (Dobes et al., 1986; Hostinsky and Cadek, 1976). The machines have a lever construction, where a creep specimen is mounted into grips connected to a hook on the top end attached to the loading lever, and to a fixed hook on the bottom end. The opposite part of the lever is loaded with a constant weight. The loading is applied on a cam located on the lever, which