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  4. Competition between intragranular and intergranular deformation mechanisms in ODS ferritic steels during hot deformation at high strain rate
 
research article

Competition between intragranular and intergranular deformation mechanisms in ODS ferritic steels during hot deformation at high strain rate

Sornin, D. L.
•
Karch, A.
•
Logé, R. E.  
2017
Journal of Materials Science

Oxide Dispersed Strengthened (ODS) ferritic stainless steels present well-known fine grains microstructures where dislocation movement is hindered by a dense precipitation of nano-oxides particles. Previous research, on the thermomechanical behavior at high temperature and strain rates, was focused on torsion tests (Karch in J Nucl Mater 459:53–61, 2014). Considering texture evolution and grain shape as indicators of the intragranular dislocation glide activity, it was shown that, for high temperature and strain rate, intragranular deformation was in competition with intergranular accommodation. The latter phenomenon was related to early damaging at grain boundaries. The occurrence of a transition phenomenon from an intragranular to an intergranular deformation mechanism, with increasing temperature, was recently confirmed by neutron diffraction spectroscopy (Stoica in Nature Commun 5:5178, 2014). In the present paper, hot extrusion (HE) tests are performed, avoiding damage due to the high stress triaxiality, and allowing further investigation of intragranular and intergranular plasticity at large strains. Three ferritic steels exhibiting various precipitation size anddensitywere hot extruded.Microstructure evolution at different stages of deformation is investigated using the Electron Back-Scattered Diffraction (EBSD) technique. After extrusion at 1373 K (1100°C), the microstructure of ODS steels consists of a mixture of small round shape grains and larger elongated grains containing low-angle grain boundaries. Texture measurements show the appearance of the a-fiber (\110[//extrusion direction) and an increase in its intensity during the extrusion process in the larger grains. The fragmentation of the large elongated grains by Continuous Dynamic Recrystallization (CDRX) partially occurs in ODS materials depending on precipitation reinforcement. For smaller grains, plastic deformation has no effect on crystallographic orientation and grain shape, indicating a grain boundary accommodation phenomenon as the major deformation mechanism. Precipitation density not only impacts the intragranular dislocation glide activity, but also reduces CDRX kinetics in coarse grains.

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Type
research article
DOI
10.1007/s10853-017-1730-1
Web of Science ID

WOS:000416544500055

Author(s)
Sornin, D. L.
Karch, A.
Logé, R. E.  

EPFL

Date Issued

2017

Publisher

Springer Verlag

Published in
Journal of Materials Science
Volume

53

Issue

4

Start page

2965

End page

2975

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LMTM  
Available on Infoscience
December 12, 2017
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/142712
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