Thermal stability and growth of nano-grained structures produced by mechanical alloying of Nb and Al

J. Saida, Y. Tanaka, K. Okazaki

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11 Citations (Scopus)

Abstract

Mechanical alloying of elemental niobium and aluminum was carried out in Argon for 180ks to produce a nanocrystalline intermetallic compound Nb3Al. The detailed analysis of XRD shows that the as-MAed product has the volume distribution of 13% Nb (4 nm), 40% Nb2Al (4 nm) and 47% Nb3Al (3.8 nm). This three-phase mixture was converted into a two-phase mixture of 19 vol.% Nb2Al and 81 vol.% Nb3Al upon heating to 873 K for 3.6 ks, the resultant grain sizes being 4.7 nm. Isochronal annealing from 873 to 1423 K revealed that a significant grain growth occurs above 1173 K to approximately 33 nm at the maximum temperature. At the respective temperatures isothermal annealing was carried out for 3.6, 7.2 and 14.4 ks to deduce the grain growth kinetics that can be described by In (dD)/dt)=ln (k/8)-7 In (D) where D is the measured grain size and k a constant, implying that the kinetics is of a high order (D to the 8th). This k is related to temperature T as k=koexp(-Q/RT) where Q is the activation energy for grain growth and R the gas constant. The Arrhenius plots of In [(D8-D08)lt] versus 1/T yield two distinct slopes, from which the activation energies of 166±5.2 and 118±3.5 kJ/mol for the grain growth of Nb3Al and Nb2 l are obtained at temperatures higher than 1173 K and below this temperature they are 74.4±4.4 and 59.6± 1 kJ/mol respectively. But the kinetic order remains the same regardless of temperature and phase.

Original languageEnglish
Pages (from-to)265-270
Number of pages6
JournalMaterials Transactions, JIM
Volume37
Issue number3
DOIs
Publication statusPublished - 1996
Externally publishedYes

Keywords

  • Grain growth
  • Kinetics
  • Mechanical alloying
  • Nanophase
  • Niobium aluminide
  • Thermal stability

ASJC Scopus subject areas

  • Engineering(all)

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