In Situ Characterization at High Temperature of VDM Alloy 780 Premium to Determine Solvus Temperatures and Phase Transformations Using Neutron Diffraction and Small-Angle Neutron Scattering

VDM 780 Premium is a recently developed Ni-based superalloy designed for working at high service temperatures (above 650 C) while keeping the good workability of alloy 718. VDM 780 Premium is based on the austenitic matrix (g phase) strengthened by intermetallic Ni 3 Al-like precipitates (g' phase, fcc L1 2 structure). Other co-precipitates may be formed in function of the applied heat treatment, such as Ni 3 Nb-based (d phase, orthorhombic DO a structure) or Ni 3 Ti-based (h phase, hexagonal DO 24 structure) precipitates. The amount as well as the size and morphology of the different precipitates depend on the heat treatments performed on the alloy, playing an important role in improving the creep properties or the behavior during forging and recrystallization. This work contains a complex study using various techniques of analytical electron microscopy and synchrotron diffraction intended to clarify the structure of the high-temperature phase formed in the newly developed VDM 780 Premium alloy. The atomic structure of the high-temperature plate-like precipitates formed in VDM 780 Premium after two different thermal treatments has been investigated in relation with the surrounding matrix lattice, proving the stacked d/h structure of the precipitates.

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“…S2 and S3). Therefore, this diffraction pattern perfectly fits the B g' ¼ [1][2][3][4][5][6][7][8][9][10] zone axis orientation of the g' phase.…”

Section: Areasupporting

confidence: 62%

“…We previously reported on the structure of the newly developed alloy VDM 780 Premium by means of neutron diffraction experiments [6,8]. However, the structure of the high-temperature phase/ phases present in the material could not be resolved, as it was found to be compatible with both the d and h phases.…”

Section: Introductionmentioning

confidence: 99%

HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

Ghica

Solís

Munke

et al. 2020

Journal of Alloys and Compounds

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“…This was also confirmed by a calculation of the mean distance of the γ′-precipitates and the diffusion length of the dissolving γ′-forming elements Al and Nb within the Ni-matrix. Previous SANS measurements [26] showed that the mean size of the γ′-precipitates is 35 nm in VDM ® Alloy 780 in its as-received condition. Assuming round γ′-precipitates, this led to a minimum distance of only 4 nm between two γ′ precipitates at a γ′ volume fraction of 35%.…”

Section: Discussionmentioning

confidence: 95%

“…The microstructure of the VDM ® Alloy 780 was previously intensively investigated by the authors by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), as well as neutron diffraction (ND) and small-angle neutron scattering (SANS) [25][26][27][28]. The microstructure consists of the γ-matrix, the γ -hardening phase, and the δ-, η-, and Nb/Mo-based high-temperature-stable carbide phases (hereinafter denoted as NbC, for clarity).…”

Section: Introductionmentioning

confidence: 99%

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

Kümmel

Fritton

Solís

et al. 2022

Metals

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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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“…The microstructure at the room and elevated temperature of VDM 780 has already been investigated in previous publications by the authors of this paper by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) as well as ND and SANS [26][27][28]. The microstructure consists of γ-matrix, hardening γ -phase, and high temperature stable δand η-phases.…”

Section: Introductionmentioning

confidence: 87%

Deformation Mechanisms in Ni-Based Superalloys at Room and Elevated Temperatures Studied by In Situ Neutron Diffraction and Electron Microscopy

Kümmel

Kirchmayer

Solís

et al. 2021

Metals

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Polycrystalline Ni-based superalloys are one of the most frequently used materials for high temperature load-bearing applications due to their superior mechanical strength and chemical resistance. In this paper, we presented an in situ diffraction study on the tensile deformation behavior of the polycrystalline Ni-based superalloy VDM® Alloy 780 at temperatures up to 500 °C performed at the STRESS-SPEC neutron diffractometer at the Heinz Maier-Leibnitz Zentrum. A detailed microstructural investigation was carried out by electron microscopy before and after testing. The results of these studies allowed us to determine the deformation mechanism in the differently orientated grains. It is shown that the deformation behavior, which is mainly dislocation motion and shearing of the γ′-precipitates, does not change at this temperature range. The deformation is strongly anisotropic and depends on the grain orientation. The macroscopic hardening can mainly be attributed to plastic deformation in grains, where the (200) lattice planes were orientated perpendicular to the loading direction. Accordingly, a remaining lattice strain and high dislocation density were detected predominantly in these grains.

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In Situ Characterization at High Temperature of VDM Alloy 780 Premium to Determine Solvus Temperatures and Phase Transformations Using Neutron Diffraction and Small-Angle Neutron Scattering

Cited by 4 publications

References 26 publications

HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

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

Deformation Mechanisms in Ni-Based Superalloys at Room and Elevated Temperatures Studied by In Situ Neutron Diffraction and Electron Microscopy

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