PSI - Issue 58

Juraj Belan et al. / Procedia Structural Integrity 58 (2024) 109–114

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Juraj Belan et al. / Structural Integrity Procedia 00 (2023) 000–000

state and the post-annealed state of IN 718 superalloy to highlight the  -matrix grain, MC carbides and δ-phase. Kallings 2 etchant (2g CuCl2 + 40ml HCl + 80ml ethyl alcohol) was used to highlight the  -matrix, MC carbides,  -phase and δ-phase in the initial state and in the state after annealing, respectively, after a high temperature fatigue test. In order to increase the color contrast of the structure and for easier identification of the structural components, the samples were observed using polarized light (PS) and differential interference contrast (DIK). Color contrast was achieved using Beraha III etchant (base solution: 50g NH4FhF + 400ml HCl + 600ml H2O, etchant: 100ml base solution + 1g K2S2O5) – this single etching was done wet. Microstructural analysis was carried out using a light microscope NEOPHOT 32 (OM) + metallographic software NIS Elements AR 5.20 and a scanning electron microscope TESCAN VEGA II (SEM, SEM+EDX, Mapping) at the Department of Materials Engineering, Faculty of Mechanical Engineering, University of Žilina in Žilina. 3. Results and discussion The evaluation of the grain size of the  -phase showed, Figs. 1a and b, that the values declared by the manufacturer were slightly different (the grain size declared by the manufacturer was G = 8.5, the value G = 11.48 was determined by measurement). The difference between the declared grain size and the calculated grain size is almost 47%. The grain size of the basic solid solution  after applied annealing did not change compared to the initial state (G = 11.48 to G = 10.62 after annealing), which was mainly due to the increased proportion of the δ-phase excluded along the grain boundaries of the solid solution  . The positive influence of the δ-phase was manifested, which effectively prevented grain growth at higher temperatures. The fundamental change in the microstructure was primarily related to the form and volume fraction of the excluded δ-phase.

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Fig. 1. Microstructure of IN 718; a) the grain size G = 11.48 at starting stage, b) the grain size G = 10.62 after annealing, etch. Beraha III, c) volume of δ-phase at starting stage, d) volume of δ-phase after annealing, etch Kallings 2, SEM.