Abstract
Ni-based superalloy 718 is especially suitable for high-temperature, high-pressure environments in aviation, where corrosion, creep, and thermal shock resistance are necessary for safe operation. The listed properties of alloy 718 are obtained by heat treatment - precipitation hardening. Heat treatment significantly affects the grain size of the basic gamma solid solution and the structural components of the alloy such as L12 gamma prime, DO22 gamma double prime and BCT delta phase. Their morphology, distribution and degradation affect the mechanical and thermo-mechanical properties of the alloy. The article aims to characterize and quantify the influence of the mentioned structural components on the dynamic properties of the alloy. For this purpose, methods of quantitative metallography using optical (differential interference contrast – DIC and dark field – DF) and scanning electron microscopes (EDS analysis, EDS elemental mapping, etc.) were used. To consider the influence of δ-phase on the dynamic properties (fatigue life) of alloy, blocky shape specimens at starting stage and after applying additional annealing (to increase the volume fraction of the δ-phase) at 800°C ± 5°C/72h + cooling in the furnace and the three-point bending fatigue test with the cycle asymmetry parameter R < 1, loading frequency f ≈ 145 Hz and Nf = 2.107 as a run-out were used.
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