Solid state reactions in Al/Ni alternate foils induced by cold rolling and annealing

Al/Ni composites made of alternate foils having overall composition Al50Ni50 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 transmitting medium. The logarithmic reduction of foil thickness scales with the number of rolling passes. A nanocrystalline state of the elements, particularly Ni, is progressively reached. No detectable reaction is caused by repeated 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, scanning electron microscopy, reproduces that found on annealing deposited multilayers and ball-milled powders: Al3Ni, Al3Ni2, NiAl. All reactions are strongly activated by deformation, i.e. they occur at lower temperature as revealed by continuous heating experiments in a differential scanning calorimeter. The overall set of experimental results is consistent with reaction mechanisms of nucleation and growth with grain-boundary interdiffusion as the rate-determining step. This view is supported by comparison with a collection of data for the activation energy of diffusion, grain growth, and ordering in Al–Ni phases.