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Nano-scale characterization of white layer in broached Inconel 718

Chen, Zhe; Colliander, Magnus Hörnqvist; Sundell, Gustav; Peng, Ru Lin; Zhou, Jinming LU ; Johansson, Sten and Moverare, Johan (2017) In Materials Science and Engineering A 684. p.373-384
Abstract

The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718. TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD... (More)

The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718. TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ' and γ'' clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Adiabatic shear band, Broaching, Inconel 718, Mechanically-based subgrain rotation, Surface integrity, White layer
in
Materials Science and Engineering A
volume
684
pages
12 pages
publisher
Elsevier
external identifiers
  • scopus:85007129832
  • wos:000393938300045
ISSN
0921-5093
DOI
10.1016/j.msea.2016.12.045
language
English
LU publication?
yes
id
834c6791-9b16-4a8e-bc11-83150dc4d372
date added to LUP
2017-02-06 10:21:01
date last changed
2018-01-07 11:48:37
@article{834c6791-9b16-4a8e-bc11-83150dc4d372,
  abstract     = {<p>The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718. TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ' and γ'' clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.</p>},
  author       = {Chen, Zhe and Colliander, Magnus Hörnqvist and Sundell, Gustav and Peng, Ru Lin and Zhou, Jinming and Johansson, Sten and Moverare, Johan},
  issn         = {0921-5093},
  keyword      = {Adiabatic shear band,Broaching,Inconel 718,Mechanically-based subgrain rotation,Surface integrity,White layer},
  language     = {eng},
  month        = {01},
  pages        = {373--384},
  publisher    = {Elsevier},
  series       = { Materials Science and Engineering A},
  title        = {Nano-scale characterization of white layer in broached Inconel 718},
  url          = {http://dx.doi.org/10.1016/j.msea.2016.12.045},
  volume       = {684},
  year         = {2017},
}