Grain refinement mechanism of nickel-based superalloy by severe plastic deformation - Mechanical machining case
By Z. Liao, M. Polyakov, O. G. Diaz, Dragos Axinte, G. Mohanty, X. Maeder, J. Michler, M. Hardy. Acta Materialia, 2019
165 citations recorded by the source corpus.
Abstract This paper studied the formation mechanism of white layer of a next generation nickel-based superalloy formed under severe plastic deformation induced by a mechanical material removal process. A graded microstructure of the white layer in the nickel-based superalloy has been revealed for the first time, which is composed of (i) a “dynamic recrystallisation” layer formed by nanocrystalline (∼200 nm) grains at the vicinity of the surface and (ii) a “dynamic recovery” layer with subgrain microstructures extending further into the subsurface. The mechanism of surface grain refinement was identified based on the results obtained via crystallographic and chemical analysis, as well as in-situ micro-mechanics experiments in the scanning electron microscope. It is found that in the top surface layer not only grain refinement but also the γ′ phase dissolution occurs, changing drastically from the bulk material. Furthermore, it is shown how the high plastic strain and cutting temperature along the subsurface causes grain refinement in the white layer and grain elongation in the subsurface. The γ′ precipitates in the recrystallisation layer are dissolved during the machining process, while the ultra-high cooling rate suppresses the further precipitation of this phase, resulting in the supersaturation of γ grains or minimized γ′ precipitates in the top surface layer. Hence, the grain refinement does not result in an increase of mechanical stiffness but a deterioration of mechanical properties due to the dissolution of the strengthening phase γ’, which leads to a lower strength and increased ductility. Machining is generally treated as a cold-working process. However, according to our findings hot-working with dynamic recrystallisation and recovery, as well as phase evolution, occurs in the white layer of nickel-based superalloys.
Subfields: Materials Chemistry, Mechanical Engineering, Mechanics of Materials
View Paper: https://www.semanticscholar.org/paper/241531f9cca5575e8de17f04b927e646b0feb9ac
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In Materials Chemistry
In Mechanical Engineering
In Mechanics of Materials
Citations in the corpus
- Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms (2021, methodology): “dislocations activities and (d) pile-ups around the grain boundary in the plastic deformation layer [65].”
- Surface integrity in metal machining - Part II: Functional performance (2021, background): “cooling rates induces a nanocrystalline WL microstructure that is highly strained, with high lattice misorientation and high dislocation densities, which results in a reduced micro-ductility [27].”