Advanced Materials
Research focus
The Peer review has evaluated this group as Excellent
The research line described in this section covers those activities related to metallurgy and processing of advanced and non-conventional metallic alloys such as nanostructured and ultrafine grained metals, aluminium and magnesium alloys for high temperature applications, metal matrix composites (MMCs) and special steels developed for the powder metallurgy (PM) fabrication route. Starting from the year 2000, large efforts were dedicated to the development of ultrafine grained (UFG) alloys having a grain size in the range 100-500 nm by the severe plastic deformation (SPD) technique. According to this method, a significant refinement of alloy microstructure is achieved by extensively straining the material at room temperature or at moderately high temperatures, thus activating the so called continuous recrystallization process. The first technological process suitable to impart plastic deformation levels of the order of 400% or more were developed for laboratory testing in late eighties and early nineties. The international research community, and accordingly also the present research group, is currently involved in a deep understanding of the evolution, stability and strengthening metallurgy of these UFG metals. Promising achievements were also obtained on the development of more industrially-based processing techniques suitable for the generation of ultrafine grained structures in industrial metalworking plants such as asymmetric rolling and caliber rolling. Extensive investigations in recent years were undertaken on the short and long term microstructural stability and mechanical behaviour especially at high temperatures, of both conventional and innovative aluminium and magnesium alloys. Relevant scientific achievements were obtained in the study of medium and long term creep behaviour and on the associated microstructural modifications of conventional and advanced aluminium alloys (e.g. 2014, 2014 modified with Ag, 2618 alloys) produced either by extrusion, forging and casting. The long term creep behaviour of such age-hardenable alloys was modelled taking into account their microstructural changes, namely the presence and evolution of the strengthening precipitates. Analogous activities were also carried out on conventional and experimental high temperature magnesium alloys containing rare earth elements, with special 117 emphasis on castability and resulting properties of parts produced by diecasting. Again, particular attention was given to the effects caused by exposure to relatively high temperatures on microstructure and related properties. Aluminium-based ceramic-reinforced composites are being extensively investigated since many years. Research projects were undertaken over the years for the processing of MMCs by conventional metalworking processes such as high temperature deformation and casting. In particular, in the period 2004-2006, fundamental and applied research studies were performed on solidification mechanisms and castability of Al alloys in the presence of solid ceramic particles (SiC reinforcement phase). Finally, a mention should be given to the research line pertaining specially developed high-performance PM steels obtained by optimizing the chemical composition and the nature of alloying additions. High mechanical properties in combination with the obvious advantages given by the PM processing route (minimum of material waste and near-net shapes obtained directly after pressing and sintering) are pursued by properly forming heterogeneous distributions of elements from powder mixes or diffusion-alloyed materials, where alloying elements with slow diffusion rates in Fe are used. Further additions of Ni and Mo allowed producing experimental powders that generated Ni-rich islands of austenite surrounded by martensite after sintering. This microstructure revealed to be play an effective role in arresting fatigue cracks, thus creating a tailored microstructure whereby martensite is able to strengthened the originally weak sinter necks.
Dipartimento di afferenza
Docenti afferenti
Full Professors
Maurizio Vedani
Associate Professors
Elisabetta Gariboldi
Assistant Professors
Fabrizio D’Errico
Barbara Rivolta