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

2011; Hindawi Publishing Corporation; Volume: 2011; Linguagem: Inglês

10.1155/2011/940634

1687-8442

Moukrane Dehmas, Jacques Lacaze, Aliou Niang, Bernard Viguier,

High Temperature Alloys and Creep

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 Ni 3 Nb precipitation associated with a smaller volume fraction of Ni 3 Al precipitates. At very long ageing times at service temperature, decomposes to the stable Ni 3 Nb phase. This latter phase is also present above the solvus and is used for grain control during forging of alloy 718. While most works available on precipitation have been performed at temperatures below the solvus, it appeared of interest to also investigate the case where phase precipitates directly from the fcc matrix free of precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases.