Investigation on the Precipitates of IN718 Alloy Fabricated by Selective Laser Melting

Abstract

The microstructure and precipitates of INCONEL 718 alloy (IN718) fabricated by selective laser melting (SLM) are investigated. The matrix is comprised of the elongated γ grains along Z direction, tilting a few degrees. The microstructure mainly consists of a cellular–columnar structure with fine first dendrite arm space of 1–1.5 µm originated from the rapid solidification rate locally. The precipitates of the SLMed IN718 are confirmed to be a significant amount of Laves in the form of irregular bulk distribution, small amount of carbonitride and spherical Al2O3 particles in nanoscale. Some of the carbonitrides grow separately and some of the carbonitrides enwrap the Al2O3 fully or partly, forming the shell structure of the Al2O3–carbonitride. The reheating effect from the following layers to the previous layers have not reached the solid-state transformation temperature of the γ′ and γ″.

Microstructure Evolution of Selective Laser Melted Inconel 718: Influence of High Heating Rates

“…The microstructure in the bottom region (B) was similar to the top region and is not shown here to avoid repetition. The γ″ and δ particles observed in this study are similar in shape and size (80 ± 34 nm), which have also been observed in the works [7,32,[34][35][36][37][38]. These phases are mostly confined at the bottom and top of the SLM samples by precipitation at the interdendritic zones close to the Laves.…”

Multi-laser scan strategies for enhancing creep performance in LPBF

“…Heat treatment results in the precipitation of strengthening precipitates such as γ'' and δ [28], as well as the dissolution of detrimental phases such as the Laves phase. Since AB specimens were not heat treated, interdendritic Laves phases and carbides were present.…”

Tailored microstructure and robust joint of Inconel 718/316L bimetallic multi-material fabricated by selective laser melting

“…This phenomenon could be explained as: ( ) initial cracks existed in the transition region ( Fig. 2(a)) propagated and grew rapidly when the samples were subjected to external load, and these places became the preferential fracture failure sites as a result of stress concentration; ( ) a lack of γ" phase strengthening [41], as well as a weaker ne grain strengthening [44] led by coarser average grain size in transition region, which had been discussed above.…”

“…The micro-hardness values of 316L region, transition region and Inconel 718 region were measured to be 383.7HV, 303.8HV and 320.7HV, respectively. Compared with the Inconel 718 region, the lower hardness value of the transition region with its microstructure dominated by columnar dendrite grains of Inconel 718 was attributed to the suppression of the γ" phase strengthening [41] caused by the formation of the Laves phase and the segregation of Nb as well as the crack initiation, which had been discussed in Fig. 4(c).…”

“…An overlapping region connected the cellular region and , with the average grain size calculated to be 1.2 and 0.7 µm, respectively. It had been reported that the ne equiaxed cellular dendrites were bene cial to reduce the segregation of Nb and form separated Laves phase particles, thus enhancing γ" phase strengthening phenomenon [41].…”