Solid state reactions in Al Ni alternate foils induced by cold rolling andannealing

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 Science Ltd. All rights reserved.