Seminarbeitrag von Dr. David Collins am 27.05.21 um 14 Uhr
Towards precipitate mechanism informed design of processing methods in nickel-based superalloys
Dr. David Collins
School of Metallurgy and Materials, University of Birmingham, UK
It is well known that single crystal and powder-based polycrystalline nickel-base superalloys inherit microstructures and properties from their processing routes. However, there remains enormous
scope to optimise such processes by utilising knowledge of the physical processes that govern gamma-prime precipitate formation and microscale deformation processes. This talk will
demonstrate how state-of-the-art characterisation methods including in-situ neutron & X-ray diffraction, high resolution electron backscatter diffraction (HR-EBSD) and atom probe
tomography (APT) are revealing precipitate behaviour that could be exploited in new alloy processing strategies. It is demonstrated, for example, during single crystal turbine blade casting,
that the solidification behaviour combined with mould constraints leads to highly heterogenous deformation patterning. The finding is significant as it is a key contributor to recrystallisation, an
unacceptable processing defect. Here, the evolution of precipitates during processing is evidently influenced by prior process history. This finding is also extremely potent in multi-component
powders used for polycrystalline superalloys, relevant to materials processed via additive manufacturing, or traditional thermomechanical processes (HIP, extrusion, forging etc.). The
powder particles themselves are often considered to comprise a supersaturated phase (gamma) only, however, they additionally exhibit regions of local composition segregation at the nanometre
length scale. The favoured gamma-prime formation mechanism is consequently spinodal decomposition, rather than classical nucleation and growth often observed from cooling
experiments. Such thermal treatments provide microstructures that differ significantly from the commonly observed multimodal gamma prime distributions, therefore providing tantalising scope
for new heat treatment control.
Zeit: Donnerstag, 27. Mai 2021 um 14 Uhr.