Microstructural Architecture, Microstructures, and Mechanical Properties for a Nickel-Base Superalloy Fabricated by Electron Beam Melting

Abstract

Microstructures and a microstructural, columnar architecture as well as mechanical behavior of as-fabricated and processed INCONEL alloy 625 components produced by additive manufacturing using electron beam melting (EBM) of prealloyed precursor powder are examined in this study. As-fabricated and hot-isostatically pressed (''hipped'') [at 1393 K (1120°C)] cylinders examined by optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive (X-ray) spectrometry (EDS), and X-ray diffraction (XRD) exhibited an initial EBM-developed c¢¢ (bct) Ni 3 Nb precipitate platelet columnar architecture within columnar [200] textured c (fcc) Ni-Cr grains aligned in the cylinder axis, parallel to the EBM build direction. Upon annealing at 1393 K (1120°C) (hot-isostatic press (HIP)), these precipitate columns dissolve and the columnar, c, grains recrystallized forming generally equiaxed grains (with coherent {111} annealing twins), containing NbCr 2 laves precipitates. Microindentation hardnesses decreased from~2.7 tõ 2.2 GPa following hot-isostatic pressing (''hipping''), and the corresponding engineering (0.2 pct) offset yield stress decreased from 0.41 to 0.33 GPa, while the UTS increased from 0.75 to 0.77 GPa. However, the corresponding elongation increased from 44 to 69 pct for the hipped components.

Structure, Texture and Phases in 3D Printed IN718 Alloy Subjected to Homogenization and HIP Treatments

“…No other phases, that are commonly associated with IN718 alloy such as γ', carbides and Laves phase, could be detected in the starting powder. This is consistent with the results obtained by Amato et al [17] for IN718 and by Murr et al [4] for IN625. Figure 7 demonstrates the melt pool morphology near the substrate layers and on the top deposited layers.…”

“…In the current work, the formation of δ-phase is in the same line as described by [41,42]. The Nb-rich regions in the interdendritic spaces of the powder and SLM-build specimens were observed in the EDS maps ( Figure 5), and were recognized as γ -phase using semi-quantitative EDS analysis, XRD refinement and literature data [4,17,28]. Homogenization treatment dissolved γ -phase partially in the matrix and promoted the formation of~35 nm thick and~1000 nm long needle-like δ-phase precipitates.…”

“…The X-ray pattern refinement was very challenging, because of the overlapping between the peaks of both phases and low quantity of γ -phase (~15 vol %). However, the white phase in the interdendritic space regions was recognized as γ -phase based on the current semi-quantitative EDS analysis and XRD refinements and from the available literature data [4,17,28]. No other phases, that are commonly associated with IN718 alloy such as γ , carbides and Laves phase, could be detected in the starting powder.…”

Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

“…EDS spot analysis (in at %) of phases 1-5 illustrated in Figure 6. Inter-dendritic regions of as-printed specimens have been observed to contain the γ strengthening phase [11,13,38,39]. MC-type carbides and Laves phase have also been reported to exist in these regions [12,[18][19][20].…”

“…Small γ precipitates were observed in SEM images of homogenized specimens as discussed in Section 3.1.2. However, γ has been reported to dissolve into the γ-matrix after HIP treatment at 1120 • C [38] for 4 h. A larger volume fraction (3.7%) of γ was detected in the top horizontal cross-section of as-printed specimens compared to the bottom cross-section (2.3%). columnar microstructure parallel to the matrix.…”