Studies of Standard Heat Treatment Effects on Microstructure and Mechanical Properties of Laser Net Shape Manufactured INCONEL 718

Abstract

Laser net shape manufacturing (LNSM) is a laser cladding/deposition based technology, which can fabricate and repair near-net-shape high-performance components directly from metal powders. Characterizing mechanical properties of the laser net shape manufactured components is prerequisite to the applications of LNSM in aircraft engine industrial productions. Nickelbased superalloys such as INCONEL 718 are the most commonly used metal materials in aircraft engine high-performance components. In this study, the laser deposition process is optimized through a set of designed experiments to reduce the porosity to less than 0.03 pct. It is found that the use of plasma rotating electrode processed (PREP) powder and a high energy input level greater than 80 J/mm are necessary conditions to minimize the porosity. Material microstructure and tensile properties of laser-deposited INCONEL 718 are studied and compared under heat treatment conditions of as deposited, direct aged, solution treatment and aging (STA), and full homogenization followed by STA. Tensile test results showed that the direct age heat treatment produces the highest tensile strength equivalent to the wrought material, which is followed by the STA-treated and the homogenization-treated tensile strengths, while the ductility exhibits the reverse trend. Finally, failure modes of the tensile specimens were analyzed with fractography.

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

“…EDS analysis showed that the atomic ratio of Fe:Nb in the white plate-like phase observed in homogenized specimens (Spot 5 in Figure 6) is 2.5:1. Although the plate-like phase could not be detected by X-ray diffraction due to a relatively small amount of precipitates, its morphology and composition are comparable with the Laves phase reported in the literature [3,19]. Qi et al [3] reported the partial dissolution of the Laves phase during solution treatment at 980 °C of laser net shape manufactured specimens.…”

“…Although the plate-like phase could not be detected by X-ray diffraction due to a relatively small amount of precipitates, its morphology and composition are comparable with the Laves phase reported in the literature [3,19]. Qi et al [3] reported the partial dissolution of the Laves phase during solution treatment at 980 °C of laser net shape manufactured specimens. Zhang et al [19] similarly observed incomplete dissolution of Laves phase in SLM specimens after solution treatment at 980 °C and double aging at 720 °C.…”

“…The melt pool morphology at each location in the vertical section is displayed in Figure 3b. The images displayed in Figure 3b were taken from the top corner of the specimen (1), the center of the specimen (2), and the bottom corner of the specimen (3). In order to accurately compare the specimens, the micrographs of other conditions are taken at the same positions.…”

“…Body-centered tetragonal γ undergoes a phase transformation to orthorhombic δ during long-term exposure to high temperatures (100 h at 700 • C and 50 h at 750 • C) [45]. Zhang et al [19] and Qi et al [3] reported the growth of the δ phase after partial Laves phase dissolution during solution treatment. Observations of homogenized specimens in this study show the dissemination and precipitation of γ more evenly into the matrix, the partial dissolution of the Laves phase, and the growth of~1-0 µm long and~0.20-µm thick δ phase precipitates.…”

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

“…The powder morphology largely depends on the powder manufacturing process: gas atomization (GA) powders are generally in spherical shape but are mostly attached with small satellite particles, rotary atomization (RA) powders are basically semi-spherical, while plasma rotating electrode process (PREP) powders are almost perfect round without satellites [53]. In addition, gas induced porosity is common in GA and RA powders, while PREP powder is noted as absent from such porosity [53][54][55]. For the aforementioned reasons, PREP powders are preferred.…”