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

[摘要] Inconel 718 is widely used because of its ability to retain strength at up to 650∘C for long periods of time through coherent metastableγ′′Ni3Nb precipitation associated with a smaller volume fraction ofγ′Ni3Al precipitates. At very long ageing times at service temperature,γ′′decomposes to the stable Ni3Nbδphase. This latter phase is also present above theγ′′solvus and is used for grain control during forging of alloy 718. While most works available onδprecipitation have been performed at temperatures below theγ′′solvus, it appeared of interest to also investigate the case whereδphase precipitates directly from the fcc matrix free ofγ′′precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains inδplates, and some unexpected contrast could be explained by double diffraction due to overlapping phases.

[学科分类] 材料工程