Direct characterization of phase transformations and morphologies in moving reaction zones in Al/Ni nanolaminates using dynamic transmission electron microscopy

► Fast phase transformations are examined in Al/Ni reactive nanolaminates. ► Results visible only by dynamic transmission electron microscopy at ns resolution. ► NiAl forms under 15 ns after reaction front in all three stoichiometries studied. ► DTEM imaging reveals a transient cellular morphology i...

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Bibliographic Details
Published in:Acta materialia 2011-05, Vol.59 (9), p.3571-3580
Main Authors: Kim, J.S., LaGrange, T., Reed, B.W., Knepper, R., Weihs, T.P., Browning, N.D., Campbell, G.H.
Format: Article
Language:English
Subjects:
Aluminum
Dynamic transmission electron microscopy
Intermetallic compounds
Intermetallics
Morphology
Nanocomposites
Nanomaterials
Nanostructure
Nickel
Nickel aluminides
Phase transformations
Rapid solidification
Thin film multilayers
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Summary:► Fast phase transformations are examined in Al/Ni reactive nanolaminates. ► Results visible only by dynamic transmission electron microscopy at ns resolution. ► NiAl forms under 15 ns after reaction front in all three stoichiometries studied. ► DTEM imaging reveals a transient cellular morphology in nonequiatomic films. Phase transformations and transient morphologies are examined as exothermic formation reactions self-propagate across Al/Ni nanolaminate films. The rapid evolution of these phases and sub-micrometer morphological features requires nanoscale temporal and spatial resolution that is not available with traditional in situ electron microscopy. This work uses dynamic transmission electron microscopy to identify intermetallic products and phase morphologies, as exothermic formation reactions self-propagate in nanolaminate films grown with 3:2, 2:3 and 1:1 Al/Ni atomic ratios. Single-shot diffraction patterns with 15 ns temporal resolution reveal that the NiAl intermetallic forms within ∼15 ns of the reaction front’s arrival in all three types of films and is the only intermetallic phase to form, as the reactions self-propagate and quench very rapidly. Time-resolved imaging reveals a transient cellular morphology in the Al-rich and Ni-rich foils, but not in the equiatomic films. The cellular features in the Al-rich and Ni-rich films are attributed to a cooling trajectory through a two-phase field of liquid + NiAl.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2011.02.030