Characterization of the Superalloy Inconel 718 After Double Aging Heat Treatment

Abstract

The application of heat treatment, by solid solution and precipitation hardening, is very important to optimize the mechanical properties of superalloys.The main phases present in Inconel 718 are: gamma prime γ′ face ordered Ni 3 (Al, Ti); gamma double prime γ″ bct ordered Ni 3 Nb; eta η hexagonal ordered Ni 3 Ti; delta δ orthorhombic Ni 3 Nb intermetallic compounds and other topologically closed-packed structures such as μ and Laves phases. δ, μ and Laves phases have low ductility, which causes losses in mechanical and corrosion properties (Fu et al. in Mater Sci Eng A 499:215-220, 2009 [1]). The heat treatment applied to Inconel 718, precipitation hardening, has two steps: solid solution and aging treatment. In first step the secondary (hardening) phases are dissolved along the matrix, as well as carbides. It is important to note that after 650°C (Durand-Charre in The microstructure of superalloys. CRC Press, Boca Raton, 1997 [2]) and with long exposure times, γ″ transforms in the stable phase δ, which results in a loss of mechanical resistance. In this study we aim to characterize the microstructure and phases in superalloy Inconel 718 during the steps of heat treatment with double aging. The double aging treatment performed followed the steps of solid solution to 1095°C/1 h and double aging at 955°C/1 h to 720°C/8 h + 620°C/8 h. The characterizations were performed through the techniques of XRD and SEM/EDS. It was possible to obtain the microstructural and phases characterizations before and after heat treatment in all steps.

Dynamic recrystallization mechanisms and twining evolution during hot deformation of Inconel 718

“…Inconel 718 is a typical Ni-based superalloy having high strength [1], excellent resistance to oxidation [2], high corrosion resistance [3,4], adequate ductility and toughness [5], favorable weldability [6] and good machining performance [7]. IN718 is used for critical parts in modern aero-engines, extrusion dies and gas-turbines [8][9][10][11][12][13][14][15][16][17]. Hot deformation is necessary to achieve the required properties in IN718.…”

Bond strength measurement for additively manufactured Inconel 718- GRCop84 copper alloy bimetallic joints

“…Heat treatment influences the strength of Inconel 718 and copper-chromium alloys through precipitation strengthening effect. Gamma prime (γ') and gamma double prime (γ") secondary phases for Inconel 718 [35], while Cr 2 Nb particles for GRCop-84 through Hall-Petch mechanism and Orowan strengthening [25]. This was obvious looking at the compressive yield strength including the elastic modulus of the bimetallic joints which increased by ~43% after thermal cycling, as shown in Fig 10. However, at these compressive yield loads, the bimetallic interfacial joints showed no sign of crack initiation/propagation along or through the interface, as observed in the backscatter electron images shown in Fig.11b and c, even at higher magnifications.…”

Creep and Mechanical Behavior Study of Inconel 718 Superalloy

“…The alloy design principles in these developments are based on maximizing the benefits that could be achieved through increased alloying contents. Because of the high alloy contents, the modern grades of superalloys require stringent control of processing to avoid precipitation of undesirable phases in the microstructure 7,[13][14][15][16] .…”