Szczegóły publikacji
Opis bibliograficzny
Analysis of microstructural evolution in alloy 718 nickel-based superalloy during long-term annealing at 760$^{\circ}$C / Grzegorz CEMPURA, Adam KRUK // Metallurgical and Materials Transactions . A, Physical Metallurgy and Materials ; ISSN 1073-5623. — 2026 — vol. 57 iss. 1, s. 403–426. — Bibliogr. s. 424–426, Abstr. — Publikacja dostępna online od: 2025-11-22
Autorzy (2)
Dane bibliometryczne
| ID BaDAP | 165617 |
|---|---|
| Data dodania do BaDAP | 2026-02-16 |
| Tekst źródłowy | URL |
| DOI | 10.1007/s11661-025-08035-5 |
| Rok publikacji | 2026 |
| Typ publikacji | artykuł w czasopiśmie |
| Otwarty dostęp |  |
| Creative Commons | |
| Czasopismo/seria | Metallurgical and Materials Transactions, A, Physical Metallurgy and Materials Science |
Abstract
Alloy 718 (UNS N077718) is commonly used in the aerospace industry, particularly in aircraft engines. In this study, a test piece made of Alloy 718 with the chemical composition Ni19Cr18.5Fe3Mo0.9Ti0.6Al0.04C (wt pct) was subjected to annealing at 760 degrees C for durations up to 1000 hours. The observed microstructural changes were compared with numerical simulations based on the CALPHAD methodology. Increasing the annealing time at 760 degrees C leads to an enlargement of the gamma ” phase, which consists of disk-shaped precipitates, and their subsequent dissolution into the gamma matrix. The matrix becomes enriched in niobium; as a result, the delta phase, coherent with the matrix, precipitates. This phase exhibits a plate-like morphology. An annealing leads to significant degradation of the microstructure. After 1000 hours, the hardness decreased from the initial state of 479 to 345 HV0.5. CALPHAD simulations are valuable input, but the precipitation simulation model underestimates the amount of gamma ' and incorrectly predicts the presence of gamma ”. A comparison of microstructural examinations with CALPHAD simulations indicates that 1000 hours at 760 degrees C is insufficient to achieve thermodynamic equilibrium. The volume fraction of phases after annealing at 760 degrees C was determined on 3D reconstructed volumes obtained using FIB-SEM tomography methods. A gamma ” volume fraction was 12.8 pct with a mean equivalent diameter = 15 nm after 50 hours, and the volume fraction increased to 13.5 pct after 250 hours. After 250, the volume fraction of delta phase was 11.6 pct. Spheroidal gamma ' precipitates with a mean diameter = 53.4 nm were found in places where gamma ” dissolved. Longer annealing times, up to 1000 hours resulted in the replacement of gamma ” phase by spheroidal gamma ' phase precipitates. Transmission Electron Microscopy methods enabled the identification of phases and the determination of crystallographic orientation between phases present in the alloy's microstructure. HRSTEM measurements indicate that the gamma phase creates a local compressive stress field in the matrix perpendicular to the gamma/gamma ” interface, specifically along the (002) gamma matrix plane. Analysis of the deformation field around the gamma ” phase precipitate resulting from lattice mismatch reveals its anisotropic nature. The stress level generated by precipitates was estimated using the Eshelby theory for elastic disk-shaped inclusions. The normal stress components in the matrix are as follows: sigma(11) = 7.882 GPa, sigma(22) = 7.882 GPa, sigma(33) = 13.306 GPa. The maximum stress develops along the direction normal to the gamma/gamma ” interface, restricting plate growth in this direction (i.e., along the plate thickness). In contrast, growth in the two orthogonal directions is thermodynamically favorable, leading to the formation of disk-shaped precipitates.
