Position of thermocouples regarding the distance from the welding bead. Thermocouples were spot welded on the sample at distances of 3, 5, 7, 10, and 13 mm from the weld line.
(a) Microstructure of as-built condition (electrolytically etched with phosphoric acid); (b) interdendritic regions in as-built condition showing (1) Laves phase and (2) MC-type carbide; and (c) bright field image of (1) Laves phase and (2) NbC carbide. The inset shows the diffraction pattern of Laves phase in γ-matrix.
(a) Microstructure of solution heat-treated (SHT) condition (electrolytically etched with oxalic acid), showing (b) precipitates residing in the grain boundaries and matrix.
(a) Microstructure of solution and aged heat treated (SHT + AGE) condition showing (b) (1) delta phase, (2) MC-type carbide, and (3) matrix with strengthening phases γ’ and γ’’ (electrolytically etched with phosphoric acid); (c) bright field image of γ’’ (marked with white arrows),the inset shows the diffraction pattern of γ’’ in γ-matrix; (d) dark field image of same area as (c), showing y’ (white particles), the inset shows the diffraction pattern of γ’ in γ-matrix; (e) TEM HAADF image showing (1) δ-phase residing on the grain boundary, (2) Laves phase, and (3) δ-phase forming from the Laves phase; and (f) TEM HAADF image of (1) NbC and (2) δ-phase residing on the grain boundary.
(a) Microstructure of HIP condition disclosing equiaxed grain structure and NbC carbides marked with arrows (electrolytically etched with oxalic acid), and (b) bright field image of carbide in HIP condition; the inset shows the diffraction pattern of carbide.
Microstructure of wrought Alloy 718 showing equiaxed grain structure and NbC carbides marked with arrows (electrolytically etched with oxalic acid).
(a) Cross section of a welded sample; (b) peak temperatures as a function of distance from weld center line; and (c) fusion zone (FZ), partially melted zone (PMZ), and heat affected zone (HAZ) of the welded sample, and the distance of these zones from the weld center line.
Heat affected zone (HAZ) cracking susceptibility of SLM-manufactured Alloy 718 in comparison with wrought Alloy 718, presented as the average of total crack length measurements, average of maximum crack length, and total number of cracks (for five observations, with standard deviations).
HAZ liquation cracking in SLM as-built condition; inset showing the marked area.
HAZ liquation cracking in SHT condition; inset showing the marked area.
HAZ of welded SHT + AGE material showing microfissure with liquation product in PMZ, and an example of grain boundary cracking without any visible liquation in the HAZ; insets showing the marked areas.
Liquation at grain boundaries causing cracking in HAZ of SLM-manufactured and HIP Alloy 718; inset showing the marked area.
Liquation cracking in HAZ of wrought Alloy 718; inset showing the marked area.
Microstructure of (a) SLM as-built, (b) wrought, and (c) cast, Alloy 718.
Chemical composition of the gas-atomized (GA) Alloy 718 powder and wrought Alloy 718. (wt. %).
Test plate conditions.
|As-built||SLM manufactured without any heat treatment|
|SHT||954 °C–1 h|
|SHT + Aging||954 °C–1 h + 760 °C–5 h + 649 °C–1 h|
|HIP||1160 °C–105 MPa–4 h|
|Mill-annealed||982 °C–4.5 min|
Chemical composition of the phases, detected in all selective laser melting (SLM) conditions, determined by the Transmission electron microscopy (TEM/EDS) and Scanning electron microscope (SEM/EDS) analyses.
|Material Condition||Phases||Elements (wt. %)|
|SLM–SHT + AGE (TEM/EDS)||Laves||58||15||15||11||4||1||0.5|
Microhardness (HV1-15 s) values of different conditions of the material. Average of 10 indents.
|As-Built||SHT||SHT + AGE||HIPed||Wrought|
|300 ± 5||280 ± 4||470 ± 7||280 ± 9||230 ± 6|