B. Brevaglieri

Hydrogen incorporation and embrittlement of electroformed Au, Cu and Au–Cu

Abstract Electroformed Au, Cu, Au–Cu layers and composites display severe brittleness in both as plated and heat treated conditions. This phenomenon has not been considered in the literature previously. In this paper we show the relevant embrittling phenomenology and explain it with the incorporation of hydrogen produced in electrochemical side reactions occurring during the formation of the metallic deposits. Our conclusions were drawn on the basis of the following experiments: (i) electrochemical measurements—proving the effect of bath composition on the hydrogen evolution side reaction—(ii) hydrogen removal tests—hot extraction and high vacuum treatments—(iii) mass spectrometric identification of released gases, (iv) SEM observations of micrometric voids, (v) SAXS measurements of nanometric voids and (vi) SEM fractography of heat treated samples. Hydrogen removal by a high vacuum room temperature treatment is proposed.

Hydrodynamic problems related to the electrodeposition of AuCu/B4C composites

Abstract Hydrodynamic actions leading to the electrodeposition of AuCu/B4C composites have been investigated experimentally and theoretically. Translation and rotation of cylindrical cathodes have been studied. Embedding of particles into disk electrodes rotating at various speeds has been analysed. The dependence of volume fraction of embedded particles on fluidisation conditions has been investigated. Higher volume fractions correlate with higher mass transport rate to the cathode and are found in points on which flow lines are closer to normal to the cathode surface (stagnation points), irrespectively of the overall flow sign. Hydrodynamic classification of particles diameters has also been observed: lower fluidisation velocities and tangential (to cathode surface) fluid flow components correlate with larger particles whilst higher fluidisation velocities and normal fluid flow components correlate with smaller particles. These effects have been modelled analytically on the basis of a hydrodynamic treatment of interactions among fluid flow, electrode surface and particles. Effects of the cathode roughness — and related local flow conditions — on particle embedding have also been disclosed and explained with the above-mentioned hydrodynamic model.

Aluminium protective coatings produced on ternary FeCrNi alloys

Protective coatings can defend a material from degradation when it is exposed to severely aggressive environments such as those encountered in the chemical, petroleum and aerospace sectors. The coating of Ni-based superalloys by diffusing aluminum has been exhaustively studied, but this is not the case where austenitic stainless steels are concerned. The purpose of the work reported here was to characterize the microstructure and microchemistry of aluminum diffusion coatings produced on stainless steels by means of preparation of synthetic alloys.