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| Home > Publications database > Near-Surface and Bulk Dissolution Behavior of $γ′$ Precipitates in Nickel-Based VDM$^®$ Alloy 780 Studied with In-Situ Lab-Source and Synchrotron X-ray Diffraction |
| Home > Publications database > Near-Surface and Bulk Dissolution Behavior of $γ′$ Precipitates in Nickel-Based VDM$^®$ Alloy 780 Studied with In-Situ Lab-Source and Synchrotron X-ray Diffraction |
| Journal Article | PUBDB-2022-03968 |
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2022
MDPI
Basel
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Please use a persistent id in citations: doi:10.3390/met12071067 doi:10.3204/PUBDB-2022-03968
Abstract: The dissolution of nano-sized Ni3Al-based $γ′$ precipitates was investigated in the newly developed polycrystalline nickel-based VDM$^®$ Alloy 780 at the surface and in the bulk region with in-situ lab-source and synchrotron X-ray diffraction. These studies are important in obtaining a deeper understanding of the strengthening mechanism responsible for the stability and long service lives of such superalloys. We found that the dissolution behavior of the $γ′$ phase is very similar at the surface and in the bulk region, but small deviations were detected. The dissolution of $γ′$ starts at around 800 °C and no $γ′$ was found at temperatures exceeding 970 °C. As a result, the elements Al and Nb, which were bound in the $γ′$ phase, dissolved into the $γ$ matrix and strongly increased the $γ$ lattice parameter, as their atomic size is larger than the $γ$-forming elements Ni, Co, and Cr. However, this effect was suppressed in the surface area. A second matrix $γ$ phase was detected at the same temperature range as that of the dissolution of the $γ′$ phase in the lab-source XRD measurements. The newly formed $γ$-2 phase had a smaller lattice parameter than that of the initial $γ$ matrix. We propose that the $γ$-2 matrix phase is a result of high-temperature surface oxidation, which consumes, among other elements, Al and Nb and, therefore, leads to the smaller $γ$ lattice parameter.
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