Al/Ni composites made of alternate foils having overall composition Al50Ni5
0 and Al66Ni34 were rolled up to 75 times folding them after every rolling
pass to restore approximately the original thickness. It was found that the
deformation of the composite is sustained by the Ni with Al acting as tran
smitting medium. The logarithmic reduction of foil thickness scales with th
e number of rolling passes. A nanocrystalline slate of the elements, partic
ularly Ni, is progressively reached. No detectable reaction is caused by re
peated co-deformation. Reactions in the composites occur on annealing. The
sequence of phases obtained at Al/Ni interfaces via nucleation and growth,
and identified by X-ray diffraction. transmission electron microscopy, scan
ning electron microscopy, reproduces that found on annealing deposited mult
ilayers and ball-milled powders. Al3Ni, Al3Ni2, NiAl. All reactions are str
ongly activated by deformation, i.e. they occur at lower temperature as rev
ealed by continuous heating experiments in a differential scanning calorime
ter. The overall set of experimental results is consistent with reaction me
chanisms of nucleation and growth with grain-boundary interdiffusion as the
rate-determining step. This View is supported by comparison with a collect
ion of data for the activation energy of diffusion, grain growth, and order
ing in AI-Ni phases. (C) 1999 Acta Metallurgica Inc. Published by Elsevier
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