PSI - Issue 80

Marie Kvapilová et al. / Procedia Structural Integrity 80 (2026) 269–278 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1: Vertical printing direction (Z-axis) Fig. 2: Schematic of creep test sample Creep specimens with a gauge length of 25 mm and a diameter of 3.5 mm were machined from the additively manufactured material (Fig 2). Uniaxial tensile creep tests under constant load were performed in a purified and dried argon atmosphere until specimen failure. The experiments were conducted at temperatures of 700°C, 800°C, and 900°C, with temperature control maintained within ± 0.5 °C of the target value. Displacement was continuously measured using a Hottinger-Baldwin inductive transducer, with a sensitivity of 5 × 10⁻⁶, with the data recorded digitally and subsequently processed. Final elongations of the fractured specimens were verified using a Gaussian comparator. The microstructural and fractographic investigations were mostly carried out using scanning electron microscopy (SEM) on the creep fracture surfaces and metallographic sections parallel to the longitudinal axis of the specimens, employing a Tescan Lyra 3 XMH FEG/SEM scanning microscope. The standard creep behaviour of the alloy can be illustrated using the creep curve, which shows the time dependence of deformation under specific loading conditions (Fig. 3a). To facilitate the identification of the individual stages of creep, a modified creep curve is often used, showing the time dependence of the creep strain rate (Fig. 3b). This relationship reveals that the secondary stage of creep is reduced to an inflection point on the curve, at which the minimum creep rate is reached. To identify the creep deformation mechanisms acting in the alloy during creep loading, the stress dependence of the minimum creep rate and the time to fracture t f at given temperatures T can be used. These dependencies can be described in the region of power-law (dislocation) creep by the empirical Norton equation (Kvapilova et al., 2019). , (1) where A is a material constant, Q C is the activation energy for creep, and R is the gas constant. The stress exponent of the creep rate n is therefore given by the following relationship. . (2) ! ! ( ) # !" A % C ' ! "#$ ! = # " ! " # ' = ) 3. Experimental results 3.1. Creep behaviour of alloy INC939 AT

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