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Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures

Chen, Z.; Peng, R. Lin; Moverare, J.; Avdovic, P. LU ; Zhou, J. M. LU and Johansson, S. (2016) In Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 47(7). p.3664-3676
Abstract

The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 °C, 550 °C, and 650 °C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in... (More)

The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 °C, 550 °C, and 650 °C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and α-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.

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type
Contribution to journal
publication status
published
subject
in
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
volume
47
issue
7
pages
13 pages
publisher
Springer
external identifiers
  • scopus:84964267890
  • wos:000377434700041
ISSN
1073-5623
DOI
10.1007/s11661-016-3515-6
language
English
LU publication?
yes
id
9242ab4b-5f7d-46f0-9546-049927802529
date added to LUP
2016-09-30 12:20:47
date last changed
2017-01-01 08:35:36
@article{9242ab4b-5f7d-46f0-9546-049927802529,
  abstract     = {<p>The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 °C, 550 °C, and 650 °C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and α-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.</p>},
  author       = {Chen, Z. and Peng, R. Lin and Moverare, J. and Avdovic, P. and Zhou, J. M. and Johansson, S.},
  issn         = {1073-5623},
  language     = {eng},
  month        = {07},
  number       = {7},
  pages        = {3664--3676},
  publisher    = {Springer},
  series       = {Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science},
  title        = {Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures},
  url          = {http://dx.doi.org/10.1007/s11661-016-3515-6},
  volume       = {47},
  year         = {2016},
}