Article ID Journal Published Year Pages File Type
1447153 Acta Materialia 2011 10 Pages PDF
Abstract

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.

► 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.

Related Topics
Physical Sciences and Engineering Materials Science Ceramics and Composites
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