121,957 research outputs found
The Sardinian newt: an endemic on the brink of extinction?
No full textLecis Roberta. The Sardinian newt: an endemic on the brink of extinction?. In: Ecologia mediterranea, tome 29 n°2, 2003. p. 255
Acciai sottoposti a trattamenti duplex; resistenza agli impatti ciclici e alla fatica
Get PDFL’impiego dei rivestimenti PVD interessa sempre un maggior numero di componenti in acciaio, non solo per garantirne un miglioramento nell’affidabilità in termini di resistenza ad usura, ma anche per assicurare miglioramenti in termini di resistenza locale ai carichi applicati, nonché incrementi di resistenza in presenza di sollecitazioni cicliche. In tale ottica si sono di recente sviluppati trattamenti “Duplex” che uniscono i vantaggi dei più tradizionali trattamenti termochimici di indurimento superficiale alla deposizione di film sottili in materiale ceramico PVD. Nel presente lavoro verranno illustrati i risultati ottenuti con prove di impatto ciclico (Impact test) su campioni di acciaio da bonifica in entrambe le condizioni bonificato o nitrurato, rivestiti con la metodica PVD. I risultati ottenuti in termini di tipo ed entità del danneggiamento hanno fornito un ulteriore parametro di valutazione in aggiunta al limite di fatica, ricavato sperimentalmente da prove di flessione rotante, in grado di suggerire l’impiego delle diverse combinazioni substrato/rivestimento in funzione delle richieste dettate dall’utilizzo. La caratterizzazione è stata completata, inoltre, da analisi microstrutturali (SEM) e di stato tensionale residuo (Rx)
Fatigue behavior of duplex-treated samples coated with Cr(C,N) film
No full textThe effect of a Cr(C,N) PVD coating on the fatigue behavior of 42CrMo4 steel grade was investigated both in a quenched and tempered condition and after nitriding treatment. The latter, so-called “duplex process”, combines a nitriding pre-treatment in order to obtain a hard and stiff substrate and
a PVD coating in order to reduce the friction coefficient and improve the wear resistance of tools and mechanical components.
Prior to fatigue testing, the surface modifications were characterized by means of X-ray diffraction (XRD), residual stress distribution, Vickers nano-hardness measurements and scanning electron microscopy (SEM) analysis.
For the quenched and tempered steels, the PVD coating acts as a high compressive residual stressed zone able to increase the fatigue resistance of the coated component. On the contrary, for the duplex-treated samples, a limited increase in the fatigue limit was detected with respect to uncoated
nitrided samples. This result was interpreted by means of the residual stress gradient which does not show high differences for nitrided coated and uncoated samples
Impact test and tribological behaviour of duplex-treated low-alloy steel
No full textThe aim of this work was the evaluation of the improvement of mechanical properties of a low-alloyed steel using a duplex treatment (nitriding+CrN 5 μm PVD). The effect on adhesion, wear, impact resistance and stiffness was investigated. The obtained results were compared to CrN coating deposed on traditional quenching and tempering substrate, heat treatment at which a 4140 steel grade is usually processed. The microstructure was analyzed by scanning electron microscopy and the mechanical properties were evaluated by nanoindentation testing, impact resistance evaluation, scratch resistance measurements and ball-on-ring wear testing under unlubricated conditions. The results showed an improved critical load, better tribological properties (friction coefficient equal to 0.1 during the wear test) and an increased behaviour in the presence of cycling impact loading conditions (up to a normal applied load of 5 GPa) for the duplextreated samples. Therefore for functional coated components an extension of duplex-treated low-alloyed
steels is expected
Resistenza all’impatto e alla fatica al variare del trattamento termico e/o del rivestimento superficiale
No full textThermoelectric Materials and Applications: A Review
No full textSolid-state energy conversion has been established as one of the most promising solutions to address the issues related to conventional energy generation. Thermoelectric materials allow direct energy conversion without moving parts and being deprived of greenhouse gases emission, employing lightweight and quiet devices. Current applications, main thermoelectric material classes, and manufacturing methods are the topics of this work; the discussion revolves around the crucial need for highly performing materials in the mid-temperature range, and around the development of more scalable fabrication technologies. The different manufacturing methods for thermoelectric bulk materials and films are also discussed. Small-scale technologies are generating increasing interest in research; the high potential of aerosol jet printing is highlighted, stressing the many advantages of this technology. A promising approach to scale the production of miniaturized thermoelectric devices that combines high energy ball milling and aerosol jet printing is proposed in the conclusion
Filosofia, scienza, valori. Il trascendentalismo critico di G. Preti, Morano Editore, Collana "Nobiltà dello spirito"
No full textInnovative coating for Electroplated Hard Chromium replacement in severe environments
No full textThe aim of this paper is the study and the characterization of new solutions for the replacement of Electroplated Hard Chromium (EHC) coatings in severe environments. Starting from the failure analysis of hard chromium at high temperature and subjected to severe wear conditions, the phenomena and mechanisms leading to coating failure were investigated and understood. From this preliminary analysis the coating main properties were identified and innovative solutions were considered and studied to check their suitability for the application.Finally, the characterization of the proposed solution was compared to the properties and the failure mechanism of similar type of coatings used in the same environmental conditions.The innovative solutions considered in this paper are electroplated double layer nickel chromium and ceramic coatings obtained by thermal spraying with different techniques, specifically a tungsten carbide in cobalt or cobalt chromium matrix by High Velocity Oxygen Fuel ( HVOF) and High Velocity Air Fuel techniques (HVAF)
Noi e loro. Un approccio comunicativo
No full textIn this essay I examine the figure of the Other according to the theory of communicative action. I will not consider the contrast between Habermas and post-modern criticism in the lessons Der philosophische Diskurs der Moderne. I will instead analyse, in the first part, the German philosopher’s stance on the contrast between Putnam and Rorty as regards ethnocentrism and relativism, focusing on the essays contained in the collection Nachmetaphysiches Denken. In the second part I will examine subsequent writings in order to show how this thesis developed to furnish an adequate theoretical account of radical cultural conflicts. On developing the concepts of Lebenswelt, Lernen, Dezentralisierung and Inklusivität, the theory of communicative reason comes to argue the functional nature of the bounds between us and the others
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