The Effect of δ Phase on the Mechanical Properties of an Inconel 718 Superalloy

• Published in: Journal of materials engineering and performance Vol. 22; no. 5; pp. 1512 - 1518
• Main Authors: Valle, L. C. M., Araújo, L. S., Gabriel, S. B., Dille, J., de Almeida, L. H.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.05.2013; Springer
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Elasticity. Plasticity; Engineering Design; Exact sciences and technology; Materials Science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Quality Control; Reliability; Safety and Risk; Tribology; microstructure; heat treatment; Inconel 718; mechanical properties; Grain size; Nickel base alloys; Delta phase; Ductility; Tensile property; Precipitate; Hardness; Grain coarsening; Forging; Solution heat treatment; Superalloy; Yield strength; Property structure relationship; Microstructure; Strength
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-012-0433-7

The relationship between the δ phase content and the mechanical properties of Inconel 718 superalloy is still uncertain in the scientific literature. This study investigated the effects of the amount of δ phase and of the grain size on the mechanical properties of an aged γ-matrix with γ′ and γ″ precipitates. The material in as-received condition in the form of a forged bar was solution-treated in different conditions and aged according to UNS7718 standard. The microstructures were characterized using optical, scanning, and transmission electron microscopy. Hardness and tensile tests were also conducted. After solution treatment, γ′ and γ″ phases are dissolved and δ phase volume fraction is reduced to a minimum amount only observed by TEM, resulting in an increase of the grain size and a decrease of hardness and strength. After aging, the precipitation of γ′ and γ″ occurs and the amount of δ phase increases. The volume fraction of δ phase varying from 0.30 to 1.38% and the grain size varying from ASTM 7 to 5 do not have a significant effect on the tensile properties and hardness.