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The ductile to brittle transition of ultrafine-grained Armco iron: an experimental study

Abstract

Fracture toughness measurements on bcc iron (Armco-iron), which is subjected to severe plastic deformation (SPD), were performed. Through high pressure torsion, an ultrafine grain structure was obtained and with subsequent heat treatments the grain size varied between 300 nm and 5 μm. The combination of SPD and individual heat treatments allows for a systematic study of the ductile to brittle transition (DBT) in the fracture behaviour as a function of grain size. Additionally, the influence of different crack plane orientations was taken into account. The results show that the DBT moves for smaller grain sizes (<1 μm) to higher transition temperatures. Furthermore, large differences in the absolute toughness values for a given temperature for the different crack plane orientations and grain sizes were determined. The findings can be related to a change in the crack path from transcrystalline fracture for grain sizes larger than 1 μm to intercrystalline-dominated fracture for grain sizes smaller than 1 μm.

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Acknowledgement

The work was partly supported by the Austrian Science Fund FWF in the framework of Research Network S 10402 N16.

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Correspondence to A. Hohenwarter.

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Hohenwarter, A., Kammerhofer, C. & Pippan, R. The ductile to brittle transition of ultrafine-grained Armco iron: an experimental study. J Mater Sci 45, 4805–4812 (2010). https://doi.org/10.1007/s10853-010-4635-9

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Keywords

  • Fracture Toughness
  • Severe Plastic Deformation
  • Linear Elastic Fracture Mechanic
  • Cleavage Fracture
  • DBTT