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De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolyte percolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au40Cu28Ag7Pd5Si20, percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.

This work deals with the effect of Ni addition on the liquid–liquid phase separation in the Cu–Co system which displays a liquid metastable miscibility gap. Cu–Co–Ni samples with different compositions have been processed by differential scanning calorimetry using a fluxing technique to precisely determine transformation temperatures. The ternary phase diagram has been evaluated by Calphad, extrapolating the binary systems and optimizing ternary parameters using the experimental results of the present work. Ni additions reduce the demixing temperature, bringing the binodal line below the peritectic. The mechanisms of demixing and formation of microstructures have been clarified for low and high Ni content.

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.