Effects of increased alloying element content on NiAl-type precipitate formation, loading rate sensitivity, and ductility of Cu- and NiAl-precipitation-strengthened ferritic steels

M. Kapoor*, D. Isheim, S. Vaynman, M. E. Fine, Y. W. Chung

*Corresponding author for this work

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

Two experimental bcc-Cu- and B2-NiAl-precipitation-strengthened ferritic steels with 6.3 at. % and 12.4 at. % Cu + Mn + Ni + Al, 950 MPa and 1600 MPa yield strength respectively, were studied. Atom probe tomography showed that the volume fraction and number density of NiAl-type precipitates in the heavier alloyed steel (designated as CF-9) is ∼60-70 times greater than those in the lighter alloyed steel (designated as CF-2). This is attributed to the smaller lattice misfit between these NiAl-type precipitates and the ferritic matrix in CF-9 due to more incorporation of Mn atoms on the Al sub-lattice in the B2 NiAl unit cell. Loading rate sensitivity of hardness was measured for CF-2, CF-9 and SAE-1090, which does not have bcc-Cu precipitates. Results show that even though CF-2 and CF-9 have double and triple the strength of SAE-1090 respectively, their hardness shows weaker dependence on loading rate. This is attributed to the presence of bcc-Cu precipitates in CF-2 and CF-9 providing athermal activation of nearby screw dislocation motion. Auger electron spectroscopy studies of CF-9 samples reveal Cu segregation on grain boundaries. The observed Cu segregation is believed to be partly responsible for the lower elongation-to-failure of CF-9 compared with CF-2.

Original languageEnglish (US)
Pages (from-to)166-171
Number of pages6
JournalActa Materialia
Volume104
DOIs
StatePublished - Feb 1 2016

Keywords

  • B2-NiAl-type
  • Bcc-Cu
  • Mechanical properties
  • Precipitation-strengthened ferritic steel
  • loading rate sensitivity

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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