PSI - Issue 42

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Petr Dymáček et al. / Procedia Structural Integrity 42 (2022) 1576–1583 Author na e / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3 Microstructures of early experiments (a) recrystallized grains b) nanodispersoid of Y 2 O 3

2.2. Mechanical testing For tensile testing of the FeAlOY, flat specimens with a gauge length of 25 mm and cross section of 2.5 mm × 3.5 mm are cut by a precise electrical discharge machine from hot rolled and secondary recrystallized FeAlOY sheets and grinded to P400. Round specimens with a gauge length of 25 mm, diameter of 4 mm and M9 threaded head are turned from the hot rotary swaged and secondary recrystallized FeAlOY bars. Tensile tests at 1100 °C and strain rate of 10 -6 s -1 are performed by using the Zwick/Roell KAPPA DS 50 kN electromechanical creep test system (Zwick/Roell, Fürstenfeld, Austria) with Zwick furnace on air. This testing machine allows wide range of strain rates for constant rate tests due to its crosshead speed between 1µm/h and 100 mm/min. Constant load creep tests are performed on in-house creep testing machines with direct dead weight loading and indirect measurement of the displacement by a Micro-Epsilon OptoNCDT laser sensor on the loading train. The grips of these creep testing machines made of Ni-based alloy Inconel 601 and 617 will have to be replaced due to their unacceptable creep deformation while testing the FeAlOY specimens at 1100 °C. The main problem is very small creep strain rate of the FeAlOY specimens in order of 10 -9 s -1 , so even very small creep deformation of the grips during long-term testing multiplies the measured strain by a factor of about 2. Currently, first assembly of FeAlOY grips produced from rotary swaged FeAlOY bars is installed and the creep test is successfully running. 3. Results and discussion Comparison of two different consolidation techniques brings interesting results, for more details see Svoboda et al. (2020). Secondary recrystallization of the hot rotary swaging consolidated specimens featuring UFG microstructure leads to rather coarse grains significantly elongated in the direction of swaging axis (see Fig. 4). Although the microstructure of nano-oxides in the secondary recrystallized grains of the FeAlOY consolidated by hot rolling is significantly more regular and finer than that of the FeAlOY consolidated by hot rotary swaging (see Fig. 5), the strength of the latter at 1100 °C is by a factor of 1.5 to 2 higher than that of the first one.