Intergranular oxidation of Ni-base alloy 718 with a focus on additive manufacturing

Abstract

The intergranular oxidation in air at 850°C of alloy 718 produced by laser beam melting and electron beam melting was compared to that of the wrought alloy. Quantitative analyses revealed that the amount of grain boundary oxidation was similar for these alloys. However, the additively manufactured ones presented deeper and thicker oxides at grain boundaries, due to grain size heterogeneity and to a smaller number of special boundaries. Results show that intergranular oxidation kinetics follows Wagner's theory on internal oxidation considering not only O diffusion at the intergranular oxide/metal interfaces but also Al and Ti diffusion in the bulk.

Cyclic oxidation of alloy 718 produced by additive manufacturing compared to a wrought-718 alloy

“…In addition, it has been shown previously [1,24] that even if the AM samples were studied in their as-built forms and compared to the heat-treated wrought sample, the three alloys -EBM, LBM and wroughthad similar oxidation resistances in terms of mass change after 3000 h in air at 850 • C. Their microstructure differences had only a small effect on the morphology of the oxide at the grain boundaries [24]. In the present study, cyclic condition at 900 • C shows that the solution heat-treatment conducted on LBM samples has a small positive effect on the adhesion of the oxide scale, which may be attributed to the homogenization of the microstructure.…”

High Temperature Oxidation of Additively Manufactured Structural Alloys

“…The recyclability of powders has been the subject of numerous studies, for example, 4 (c) unmelted powder particles fully oxidized (A), TA6V EBM (SEM-SE), 5 (d) special grain boundaries (B in blue, green, red, yellow) without any intergranular oxidation (C in black) (electron backscatter diffraction). 6 for titanium alloy TA6V and superalloy 718. 11,[13][14][15] The results show overall that it is possible to maintain a very low pollution with the LBM and EBM processes for these two alloys, even after dozens of cycles.…”

“…4). 6 Ramenatte et al 23 compared the air oxidation of alloy 625 produced by LBM or casting and rolling. The LBM alloy exhibits a cellular microstructure with significant segregations of Nb and Mo.…”

“…The nature of grain boundaries may be different from those observed in materials from conventional elaboration processes, due to increased segregation, pore closures during HIP, texturing, and internal stresses, and this may affect high-temperature intergranular oxidation kinetics. 6 5. The resistance to cyclic oxidation and hot corrosion has been scarcely reported in the literature.…”

Isothermal short‐term oxidation behavior of MAR‐M246 nickel‐based superalloy at 800°C and 1000°C

“…Although thermodynamic simulations do not directly represent phase formation in an oxidized sample because they do not consider the diffusion of alloying elements, they reveal the location of the different oxides, starting from the surface toward the substrate, as oxygen pressure decreases. [18,19] At 800°C, for a pO 2 of 10 −26 to 10 −17 atm, the Corundum 1 and 2 oxides, Al 2 O 3 and Cr 2 O 3 respectively, appear in thermodynamic equilibrium with the γ phase, indicating possible internal oxidation with a greater amount of Al 2 O 3 , mainly below 10 −24 atm. For the pO 2 range of 10 −17 to 10 −14 atm, a greater quantity of XY 2 O 4 spinel (calculated as Ni(Al, Cr) 2 O 4 ) is expected, with a concomitant decrease in the content of Cr 2 O 3 and γ phase and the absence of Al 2 O 3 .…”