Atomic-scale analytical imaging to understand deformation mechanisms in superalloys

Atomic-scale analytical imaging to understand deformation mechanisms in superalloys

Understanding the deformation mechanisms observed in high performance materials, such as superalloys, allows us to design strategies for the development of materials exhibiting enhanced performance. In this project, we focus on the combination of structural information gained from electron microscopy and compositional measurements from atom probe tomography (APT).

New insights into these mechanisms can now be gained through systematic, high-resolution characterisation, enabled by advanced characterisation methods that offer spatially resolved quantification of deformation and composition. In this project, we focus on the combination of structural information gained from electron microscopy Understanding the deformation mechanisms observed in high performance materials, such as superalloys, allows us to design strategies for the development of materials exhibiting enhanced performance. and compositional measurements from atom probe tomography (APT).

Although the dissolution of γ’ precipitates is often investigated, the exact mechanism controlling this process is not clear. It is often assumed, but not yet proven, that diffusion of solutes along dislocations via pipe diffusion enhances the dissolution kinetics of γ’ precipitates. Utilising the controlled electron channelling contrast imaging (cECCI) method, we have identified high dislocation density regions in deformed single crystal and polycrystalline superalloys and analysed dislocations by atom probe tomography (APT).

Our results show quantitative, near-atomic scale segregation of chromium and cobalt at dislocations and their diffusion along them via pipe diffusion. Direct observations of the segregation of these particular γ-stabilizing solutes allows us to elucidate the physical mechanism where pipe diffusion initiates the deleterious dissolution of γ’ precipitates and subsequently degrades the properties of superalloys of industrial relevance.

Figure 1: a) cECCI micrograph showing a high dislocation density in the fully rafted γ/γ' microstructure of a single-crystal nickel-based superalloy. b) Atom probe reconstruction from a rafted γ' precipitate, showing dislocations within a γ' precipitate. c) 1D concentration profile perpendicular to a dislocation revealing segregation of chromium and cobalt at partial dislocations and at the planar defect.

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