On the formation of hierarchically structured L21 -Ni 2TiAl type precipitates in a ferritic alloy

C. H. Liebscher*, V. Radmilovic, U. Dahmen, M. Asta, G. Ghosh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

This study demonstrates a processing sequence used to generate coherent, two-phase L21 -Ni2TiAl/B2-NiAl precipitates in a ferritic matrix, and documents their microstructural evolution. Dark-field and energy-filtered transmission electron microscopy in combination with energy-dispersive X-ray analysis are used to determine the structure and composition of the different phases in the course of the processing and aging treatment. Through rapid solidification, coherent L2 1 -Ni 2TiAl type precipitates with an internal network of curved, isotropic 1/2〈100〉 antiphase boundaries form within the bcc-Fe matrix. The average width of the precipitates in the as-quenched state is 15 nm. During the subsequent aging heat treatment thin, anisotropic B2-NiAl zones are established, resulting in a three-tiered hierarchical microstructure. The L2 1 -Ni2TiAl precipitates are coherent with the bcc-Fe matrix, while the fine B2-NiAl zones are coherently embedded in the Ni2TiAl precipitates and aligned along the 〈100〉 directions. The L2 1 -Ni2TiAl parent precipitates have a width of 40 nm in the heat-treated stage and the B2-NiAl zones are 3-7 nm wide. Hence, the addition of Ti to Fe-rich Fe-Ni-Al alloys leads to the formation of coherent L21 -Ni2TiAl precipitates in the bcc-Fe matrix with an internal network of fine, anisotropic B2-NiAl zones arranged in a hierarchical manner. These microstructures are of potential interest for designing and optimizing the mechanical properties of precipitation-strengthened ferritic alloys.

Original languageEnglish (US)
Pages (from-to)2067-2075
Number of pages9
JournalJournal of Materials Science
Volume48
Issue number5
DOIs
StatePublished - Mar 2013

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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