1,721,166 research outputs found
Metallurgia di base per l’ingegneria
No full textIl testo è rivolto agli studenti dei corsi di ingegneria con l’intento di fornire una formazione di base sulla metallurgia. Nei primi tre capitoli sono trattate le nozioni di metallurgia fisica che sono di supporto ai capitoli successivi in cui vengono trattati argomenti più pratici finalizzati all’ingegneria. In particolare viene trattato il legame metallico e i reticoli cristallini tipici dei metalli. Successivamente vengono descritti i difetti presenti nei reticoli cristallini che profondamente influenzano le caratteristiche fisiche, meccaniche e di lavorabilità dei metalli e delle leghe metalliche. Vengono infine esaminate le trasformazioni di fase liquido–solido e i diagrammi di stato la cui conoscenza è fondamentale per un corretto impiego dei materiali, per le loro lavorazioni e per valutarne i limiti di applicazione. Seguono due capitoli in cui vengono descritte le principali caratteristiche meccaniche dei metalli e leghe (limite elastico, carico di rottura, modulo elastico, durezza, tenacità e usura) e le prove per determinarle, considerando tutti i fattori che influenzano profondamente tali caratteristiche. Nel sesto capitolo vengono trattati i principali trattamenti termici finalizzati all’ottenimento di determinate caratteristiche meccaniche e di lavorabilità. Gli ultimi tre capitoli sono rivolti al comportamento meccanico dei materiali se soggetti a particolari condizioni operative: quando operano a temperature elevate (fenomeno dello scorrimento viscoso), quando sotto particolari condizioni di lavorazione o ambientali con presenza di difetti sono soggetti alle leggi della meccanica della frattura elasto–plastica, o quando soggetti a carichi ciclici subiscono il fenomeno della fatica. Seguono due appendici. Nella prima vengono presentate e descritte sinteticamente le principali leghe metalliche di maggior uso ingegneristico. Nella seconda vengono descritte le tecniche di preparazione dei provini metallografici e le principali metodologie di indagine e osservazione delle strutture delle leghe e delle loro superfici di frattura
Cold roll bonding and annealing process to produce an intermetallic layer on Ti substrate
No full textTitanium is characterized by poor resistance against oxidation at high temperature. Surface modification by formation of titanium aluminide coatings would be effective to improve oxidation resistance. In this study, a 100 μm aluminum foil was initially bonded with a 1 mm Ti sheet by means of cold roll bonding. The aluminum clad Ti foil was heat treated over the temperature range 600-1000°C in order to form an outer TiAl3 layer protecting the substrate from high temperature oxidation. Al and Ti concentration profiles, as well as microhardness profiles, were determined in order to investigate the relationship between heat treatment conditions and formation of intermetallic compounds. The morphology and the structure of TiAl3 layer formed at different temperatures were studied by means of SEM/EDS and X-ray diffraction
Isothermal oxidation behaviour of TiAl-Cr-Nb-B alloys produced by induction melting
No full textThe oxidation behaviour of Ti-48Al-2Cr-1.5Nb-0.04B, Ti-48Al-2Cr-3Nb-0.04B, Ti-48Al-2Cr-6Nb-0.04B alloys were investigated by thermogravimetric method. Isothermal experiments were carried out at 900 degrees C and 1000 degrees C in air. The work focused on the synergistic effect of Cr and Nb on the oxidation resistance of the considered alloys when Nb content was increased from 1.5% at. to 6% at. The alloy's microstructure and composition as well as the composition distribution of the oxide scale were analysed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffractometry (XRD). The results showed that the scale composition changes with the Nb content in the alloy and that, by increasing the Nb percentage, the mass gain decreases and the scale adherence increases, with a consequent overall improvement of the oxidation resistance. (C) 2012 Elsevier Ltd. All rights reserved
Aes rude from excavation in the sancituary of Pyrgi (Santa-Severa - Rome) [Studio archeometallurgico preliminare su aes rude del santuario etrusco di Pyrgi]
No full textThis paper reports the results of preliminary study carried out on one of the many aes rode from excavation in the Sanctuary of Pyrgi (Santa Severa - Rome) near the port of Caere (Cerveteri), one of the main towns of southern Etruria. The findings in this area of the Sanctuary, which include a large number of votive offerings mainly dating the 5th and 4th centuries B.C., bear witness to constant workship up to the end of the 3rd century B.C. The aes rude found in the southern area of the sanctuary consists of two different groups. The aim of analyses, so far carried out on aes rude, is to gain information on metallurgy techniques and to determine the provenance quarries of the raw materials, within the broader framework of a study on metallurgy, sources of supply and circulation of raw materials in South Etruria. Qualitative analyses were carried out for information on the various components, and impurities. EDS analyses on the sample show that it is made of copper almost pure, X-ray analyses reveal wide copper areas, chloride zones, and iron-oxide inclusions. There are, also sulphides and little inclusions with the mean following composition: 22% Cu, 66% Bi, 4% Pb. As is not present. The studied aes rude is different in composition to previously studied similar objects, suggesting that its ore came from not actually known mineralized areas with such a composition (namely presence of Bi, and lack of As) was mined. This aes rude is probably of an earlier period in respect to that coming from nearer areas or from the second groups from the same area. Further studies on samples from second group will improve the knowledgments and will resolve some open questions
The role of Cr, Al and Mn in the resistance of refractory steels to hot salt corrosion from combustion deposits
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