Relationship between macro/nano instrumented indentation properties and microstructure in ultrafine and nanocrystalline structure metallic systems

The mechanical behaviour of Al-Li alloys, electrodeposited Ni-Fe alloys, high-speed steels and WC-based cermets is investigated by means of the instrumented indentation test, in force of its increasing scientific and industrial interests in terms of its localised, quick, easy and non-destructive features. Various maximum loads, from nano- to macro-ranges, are employed to sense the material microstructure on different scales. Special attention is payed to ultrafine and nanocrystalline structures. Efforts have been made to find a direct correlation at local (nano- and macro-) scale between indentation properties and microstructure, being analysed both morphologically and analytically by (optical and scanning electron) microscopy and energy dispersive X-ray spectroscopy (EDS), respectively. Al-Li alloys, electrodeposited Ni-Fe alloys, high-speed steels and WC-based cermets are crucial materials for a wide range of strategic engineering applications in the light-weight transportation structures, magnetic devices, tribological coatings and cutting tools fields. The capacitor discharge welding is investigated as a key technology suitable to join similar and dissimilar materials by preserving the initial either ultrafine or nanocrystalline structure of the selected alloy. Its unique features are demonstrated in the case of Al-Li alloys and high-speed steel/WC-Co composite. The high energy density released by the capacitor discharge source during heating, along with its ability in promoting extremely fast cooling, allows to control recrystallization phenomena in aluminium alloys which origin and mechanism are still object of discussion in the scientific community