Microstructural Changes in Inconel 625 Alloy Fabricated by Laser-Based Powder Bed Fusion Process and Subjected to High-Temperature Annealing

Abstract

The microstructure of the laser powder bed additively manufactured Inconel 625 in post-build stress-relief annealed condition and subsequently annealed at a temperature of 600°C for 5, 100 and 500 h was investigated by means of light microscopy as well as scanning and transmission electron microscopy. Stressrelieved Inconel 625 exhibited fine cellular-dendritic microstructure characterized by the high dislocation density. Selected area electron diffraction studies allowed to demonstrate that already after 5 h of annealing at a temperature of 600°C, precipitation of the c¢¢ phase in the form of coherent nanoparticles occurred. With the prolongation of the duration of annealing at a temperature of 600°C from 5 to 500 h, the gradual dissolution of intercellular areas and decrease in the dislocation density were accompanied by enhanced precipitation of the c¢¢ phase nanoparticles.

Semi-Hybrid CO2 Laser Metal Deposition Method with Inter Substrate Buffer Zone

“…Structure of the material manufactured by S-HDM is similar in the upper layers; however, in the first layer, due to a slower solidification process, longer dendrites can be observed. A similar situation can be observed in the powder deposition method [ 37 ].…”

Microstructural Development in As Built and Heat Treated IN625 Component Additively Manufactured by Laser Powder Bed Fusion

“…Extended exposure to heat in the thin section resulting from a slower cooling rate may also decrease the residual stress, and potentially, lower the dislocation density. It has been shown that AM parts have a large dislocation density, on the order of \ 2 * 10 14 dislocations/m 2 , [22,37] similar magnitudes found in cold worked metals. [38] A higher magnitude of residual stress and dislocation density should lead to a faster recovery and recrystallization rate.…”

“…Marchese et al [26] and Kreitcberg et al [27] have also investigated the microstructure and mechanical properties of LPBF IN625 before and after various heat treatments. [13,22,[26][27][28] Consistently, the as-built microstructure consisted of columnar grains with a sub-grain cellular-solidification structure. After a series of heat treatments consisting of stress-relief, possible hot isostatic pressing (HIP), and solution annealing, the columnar grains became more equiaxed and the sub-grain cellular-solidification structure was dissolved.…”

“…Repeated melting and rapid solidification characterized by high cooling rate in LPBF has been shown to cause high residual stress, large dislocation densities, and high angle grain boundaries. [7,18,22] Therefore, a multi-step heat treatment using various temperatures for stress relief and solution anneal has been examined. A typical stress relief for cast IN625 is performed between 650 and 870°C for 1-2 h. [23] However, the application of this standard stress relief treatment on LPBF IN625 has been shown to incur precipitation of the d-phase.…”

Towards Automatic Detection of Precipitates in Inconel 625 Superalloy Additively Manufactured by the L-PBF Method

“…Inside them, fine grains with a very fine cellular-dendritic structure are present. The non-equilibrium solidification conditions promote the microsegregation of alloying elements and formation of nano-precipitates, as well as the substructure of dislocation cells [ 2 , 3 , 4 , 5 , 6 , 7 ].…”