TEM Study of High-Temperature Precipitation of Delta Phase in Inconel 718 Alloy

By M. Dehmas, J. Lacaze, A. Niang, B. Viguier. 2011

138 citations recorded by the source corpus.

Inconel 718 is widely used because of its ability to retain strength at up to 650∘C for long periods of time through coherent metastable 𝛾 Ni3Nb precipitation associated with a smaller volume fraction of 𝛾 Ni3Al precipitates. At very long ageing times at service temperature, 𝛾 decomposes to the stable Ni3Nb 𝛿 phase. This latter phase is also present above the 𝛾 solvus and is used for grain control during forging of alloy 718. While most works available on 𝛿 precipitation have been performed at temperatures below the 𝛾 solvus, it appeared of interest to also investigate the case where 𝛿 phase precipitates directly from the fcc matrix free of 𝛾 precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in 𝛿 plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases.

Subfields: Aerospace Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/ae976a0484d0df568f263a666143195daa47839d

Citations in the corpus

• A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718 (2017, unknown): “The composition of the d phase is also Ni 3 Nb but the structure is orthorhombic with the following lattice constants a ¼ 0.5114, b ¼ 0.4244 nm, and c ¼ 0.4538 nm (Dehmas et al., 2011; Fang et al.,1992).”