Optimization of the heat treatment of additively manufactured Ni-base superalloy IN718

Abstract

Additive manufacturing (AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM of IN718 by selective laser melting results in a very fine dendritic microstructure with a high dislocation density due to the fast solidification process. The complex phase composition of this alloy, with three different types of precipitates and high residual stresses, necessitates adjustment of the conventional heat treatment for AM parts. To find an optimized heat treatment, the microstructures and mechanical properties of differently solution heat-treated samples were investigated by transmission and scanning electron microscopy, including electron backscatter diffraction, and compression tests. After a solution heat treatment (SHT), the Nb-rich Laves phase dissolves and the dislocation density is reduced, which eliminates the dendritic substructure. SHT at 930 or 954°C leads to the precipitation of the δ-phase, which reduces the volume fraction of the strengthening γ′-and γ′′-phases formed during the subsequent two stage aging treatment. With a higher SHT temperature of 1000°C, where no δ-phase is precipitated, higher γ′ and γ′′ volume fractions are achieved, which results in the optimum strength of all of the solution heat treated conditions.

Effect of Conventional Heat Treatments on the Microstructure and Microhardness of IN718 Obtained by Wrought and Additive Manufacturing

“…According to the literature, in order to control the microstructure and mechanical properties of the AM parts by using conventional aging heat treatment, it has been proposed to modify the time and temperature of the solution treatment and to include an additional homogenization heat treatment before the solution treatment (Ref 4,19,28,29). However, these modifications do not optimize the microstructure.…”

Temperature‐Dependent Dynamic Strain Aging in Selective Laser Melted 316L

“…[13] It can be assumed that heat treatments between 800 and 1000 C lead to a reduction in the dislocation density and the residual stresses. [6,39,40] A higher-resolution image (Figure 3b) of the heat-treated condition shows an area where the substructure has vanished and left parallel line patterns (see arrow). In accordance with the studies by Man et al [41] and Kong et al, [39] the still visible patterns at the cell boundaries are due to dislocations.…”

Metal fused filament fabrication of the nickel-base superalloy IN 718

“…The presented study investigates MF 3 as a low-cost additive manufacturing (AM) method for IN 718 parts as opposed to powder bed fusion (PBF) or direct energy deposition (DED) methods that have been investigated by other researchers [20][21][22]. In this study, the influence of the debinding atmosphere on the resulting density and microstructure is compared for air, argon atmosphere and vacuum.…”