Metal matrix composite: structure and technologies

I compositi a matrice metallica sono materiali aventi elevate potenzialità di applicazione, i cui punti critici riguardano soprattutto le tecnologie di produzione e le lavorazioni alle macchine utensili. Un composito a matrice di titanio rinforzato con lunghe fibre unidirezionali in SiC, il Ti6Al4V-SiCf, è candidato per componenti di turbine aeronautiche soggette a medie temperature (fino a 600°C) per lunghi tempi di esposizione. Per questo ne sono state esaminate sia le reazioni di tipo microchimico, le quali accadono soprattutto nell’interfaccia fibra/matrice, sia le proprietà meccaniche. La microstruttura allo stato tal quale e dopo lunghi trattamenti termici (fino a 100 ore e 600°C) è stata esaminata mediante diffrazione ai raggi X (XRD), spettrometria elettronica (SEM/EDS), spettroscopia di fotoemissione (XPS) e spettroscopia Auger (AES). Il comportamento meccanico, anche qui sia allo stato tal quale che dopo trattamenti termici, è stato studiato attraverso prove ad indentazione strumentata (FIMEC), di modulo dinamico, prove di trazione e di fatica. Inoltre sono state eseguite prove di frizione interna per verificare il caratteristico comportamento anelastico del materiale, durante condizioni di elevato stato vibrazionale e di alta temperatura. Lo studio, sviluppato sullo stesso composito prodotto però mediante due processi di fabbricazione differenti come Hot Isostatic Pressure and Roll Diffusion Bonding, ha confermato l’idoneità del materiale alle applicazioni considerate. Per quanto riguarda lo studio della lavorabilità, sono stati studiati, dal punto di vista dell’operazione di foratura, i materiali compositi a matrice di alluminio rinforzati a fibre corte o particolato, valutando le migliori condizioni di riduzione delle forze di taglio, soprattutto in funzione delle temperatura del pezzo da forare.Metal matrix composites are materials having high application potentiality, whose critical points regards especially production technology and machining. A titanium matrix composite reinforced by unidirectional SiC fibers, Ti6Al4V-SiCf , is candidate to components of aeronautical turbines subjected at middle temperatures (500-600°C) for long exposure time. It has been examined about the micro-chemical reactions, occurring especially on the fiber-matrix interface, and the mechanical properties. The microstructure, in as-fabricated condition and after long-term heat treatments simulating the work condition has been investigated by means of high-temperature X-ray diffraction (XRD), energy dispersion spectrometry (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The mechanical behaviour, in as-fabricated condition and after heat treatments, have been inspected by instrumented indentation (FIMEC), dynamic modulus, tensile and fatigue tests. Moreover, to the verify the characteristic anelastic phenomena for the composite, internal friction probes have been carried out by using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibration. The study has been developed on the same composite produced by two different fabrication process, Hot Isostatic Pressure and Roll Diffusion Bonding, confirming the suitable of the material for the considered applications. About the composite machining, aluminium matrix composite reinforced by short fiber or particle has been studied about drilling operations, evaluating the better condition to reduce the cutting forces (thrust and torque), especially as function of the workpiece temperature (hot drilling

Evaluation of Microstructure Quality in Ductile Irons Based on Tensile Behaviour Analysis

Dislocation-density-related equations were proved to be promising tools to correlate tensile plastic behaviour and microstructure in ductile irons (DIs), revealing distinct relationships between equation parameters and microstructure features in austempered ductile irons (ADI) and isothermed ductile irons (IDI). These equations resulted to be successful also in the characterization of the austempering process through the plastic behaviour analysis of tensile tests of an ADI 1050 that was quenched at different times during austempering. The equation parameters could indeed be correlated to the time window for the best ausferrite, and could predict the precipitation of the deleterious ε' carbides for long austempering times. In the present work the results of the tensile plastic behaviour analysis of different DIs through dislocation-density-related equations are reported. The aim of the analysis was to test the capability of these equations to assess the microstructure quality of DIs and support their industrial production

Integrazioni alla flora vascolare dell\u2019Italia centrale. Secondo contributo

Additions to the vascular flora of central Italy. Second contribution. In this paper, new floristic records for 55 taxa for central Italy are reported. In particular, 39 taxa are native and 16 aliens, 9 are new or confirmed to Abruzzo, 1 to Marche, 21 to Molise, 16 to Umbria, 1 is excluded from the flora of Abruzzo, 1 from Molise and 1 from Lazio. Furthermore, new distribution data for 2 rare species in Abruzzo and Molise are reported

Modellazione e simulazione di sistemi domotici per la gestione dell'energia

Il seguente lavoro si occupa della modellazione di sistemi domotici basata sulla teoria dei Multi Agent Systems (MAS). Il prodotto del lavoro è la messa a punto di un ambiente di simulazione/emulazione complesso in grado di contenere al suo interno numerosi componenti di un sistema domotico. Il lavoro svolto ha portato alla collaborazione con diversi Enti di Ricerca ed Aziende del settore. Per un corretto processo di modellazione di un sistema domotico è necessario approfondire gli aspetti che ne caratterizzano la struttura e gli elementi (Agenti) che la popolano. Per quanto riguarda la struttura del modello, ci si è rifatti all’approccio MAS che verrà usato come impostazione preliminare. Questo approccio si presta molto bene alla descrizione di ambienti domotici perché possiamo pensare agli elementi che li costituiscono come agenti, ognuno dei quali ha i suoi obbiettivi e le sue necessità. Per raggiungere questo obbiettivo ci si è basati su di un approccio UML, che ha consentito di andare a concentrare all’interno delle descrizioni informazioni eterogenee, quali quelle di Agenti che possono essere anche molto differenti gli uni dagli altri. Poiché durante il processo di sviluppo dell’ambiente è necessario confrontarsi con un’ampia varietà di strumenti, tecnologie e livelli tecnici dei collaboratori, l’UML ci consente di formalizzare rappresentazioni che rimangono valide e significative in contesti diversi. Gli agenti che in questo lavoro vengono modellati sono oggetti ibridi, caratterizzati da una dinamica a stati finiti, che rappresenta il loro comportamento, e una componente descritta da una Petri Net (PN) che modella la loro interazione con la fonte energetica. Lo strumento di simulazione verrà inoltre utilizzato per testare strategie di controllo atte a rispettare i vincoli del sistema quali la limitata disponibilità di risorse o ulteriori specifiche che si vuole che il sistema rispetti

Metal matrix composite: structure and technologies

I compositi a matrice metallica sono materiali aventi elevate potenzialità di applicazione, i cui punti critici riguardano soprattutto le tecnologie di produzione e le lavorazioni alle macchine utensili. Un composito a matrice di titanio rinforzato con lunghe fibre unidirezionali in SiC, il Ti6Al4V-SiCf, è candidato per componenti di turbine aeronautiche soggette a medie temperature (fino a 600°C) per lunghi tempi di esposizione. Per questo ne sono state esaminate sia le reazioni di tipo microchimico, le quali accadono soprattutto nell’interfaccia fibra/matrice, sia le proprietà meccaniche. La microstruttura allo stato tal quale e dopo lunghi trattamenti termici (fino a 100 ore e 600°C) è stata esaminata mediante diffrazione ai raggi X (XRD), spettrometria elettronica (SEM/EDS), spettroscopia di fotoemissione (XPS) e spettroscopia Auger (AES). Il comportamento meccanico, anche qui sia allo stato tal quale che dopo trattamenti termici, è stato studiato attraverso prove ad indentazione strumentata (FIMEC), di modulo dinamico, prove di trazione e di fatica. Inoltre sono state eseguite prove di frizione interna per verificare il caratteristico comportamento anelastico del materiale, durante condizioni di elevato stato vibrazionale e di alta temperatura. Lo studio, sviluppato sullo stesso composito prodotto però mediante due processi di fabbricazione differenti come Hot Isostatic Pressure and Roll Diffusion Bonding, ha confermato l’idoneità del materiale alle applicazioni considerate. Per quanto riguarda lo studio della lavorabilità, sono stati studiati, dal punto di vista dell’operazione di foratura, i materiali compositi a matrice di alluminio rinforzati a fibre corte o particolato, valutando le migliori condizioni di riduzione delle forze di taglio, soprattutto in funzione delle temperatura del pezzo da forare.Metal matrix composites are materials having high application potentiality, whose critical points regards especially production technology and machining. A titanium matrix composite reinforced by unidirectional SiC fibers, Ti6Al4V-SiCf , is candidate to components of aeronautical turbines subjected at middle temperatures (500-600°C) for long exposure time. It has been examined about the micro-chemical reactions, occurring especially on the fiber-matrix interface, and the mechanical properties. The microstructure, in as-fabricated condition and after long-term heat treatments simulating the work condition has been investigated by means of high-temperature X-ray diffraction (XRD), energy dispersion spectrometry (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The mechanical behaviour, in as-fabricated condition and after heat treatments, have been inspected by instrumented indentation (FIMEC), dynamic modulus, tensile and fatigue tests. Moreover, to the verify the characteristic anelastic phenomena for the composite, internal friction probes have been carried out by using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibration. The study has been developed on the same composite produced by two different fabrication process, Hot Isostatic Pressure and Roll Diffusion Bonding, confirming the suitable of the material for the considered applications. About the composite machining, aluminium matrix composite reinforced by short fiber or particle has been studied about drilling operations, evaluating the better condition to reduce the cutting forces (thrust and torque), especially as function of the workpiece temperature (hot drilling

The role of particle ripening on the creep acceleration of Nimonic 263 superalloy

Physically based constitutive equations need to incorporate the most relevant microstructural features of materials to adequately describe their mechanical behaviour. To accurately model the creep behaviour of precipitation hardened alloys, the value and the evolution of strengthening particle size are important parameters to be taken into account. In the present work, creep tests have been run on virgin and overaged (up to 3500 h at 800 ∘C) Nimonic 263, a polycrystalline nickel base superalloy used for combustion chambers of gas turbines. The experimental results suggest that the reinforcing particle evolution is not the main reason for the creep acceleration that seems to be better described by a strain correlated damage, such as the accumulation of mobile dislocations or the grain boundary cavitation. The coarsened microstructure, obtained by overageing the alloy at high temperature before creep testing, mainly influences the initial stage of the creep, resulting in a higher minimum creep rate and a corresponding reduction of the creep resistance

Effect of Cr and Mn addition and heat treatment on AlSi3Mg casting alloy

In the present paper the effect of heat treatment on an AlSi3Mg alloy with and without Cr and Mn addition was investigated. Beside the well-known modification of the morphology of Fe-containing intermetallics, it was found that Cr and Mn allowed the formation of dispersoids in the aluminium matrix after solution heat treatment at 545 °C, as shown by scanning transmission electron microscope observations. These particles were responsible of the enhanced Vickers microhardness of the aluminium matrix in comparison with the base alloy after solution treatment and quenching, according to dispersion hardening mechanism. The presence of these particles was not affected by ageing treatment, which instead allowed the precipitation of β-Mg2Si, as shown by the elaboration of differential scanning calorimeter curves. The formation of dispersoids and the study of their effect on mechanical properties can represent an interesting development for applications at high temperatures of casting alloys due to their thermal stability compared to other strengthening phases as β-Mg2Si

The Correlation between Solidification Rates, Microstructure Integrity and Tensile Plastic Behaviour in 4.2 wt.% Silicon Strengthened Ductile Iron

High Silicon Strengthened Ductile Iron (HSiSDI) with 4.2 wt.% of silicon was produced in Y-blocks with different thicknesses to investigate the effects of the solidification rate on microstructure integrity and tensile mechanical properties. With decreasing solidification rates, the graphite degeneracy with the appearance of chunky graphite became more significant at the highest silicon contents, so chemical ordering and graphite degeneracy seemed to be qualitative explanations of tensile property degradation. However, a deeper analysis of the relationship between solidification rate, microstructure and tensile properties was realized through an innovative approach based on the Matrix Assessment Diagram (MAD), where the parameters of Voce equation resulting from best-fitting the experimental tensile flow curves of a significant number of HSiSDI samples, were plotted. For 3.5 wt.% silicon content, the MAD analysis indicated that the microstructure was sound for any solidification rate, while for 4.5 wt.% the microstructure was sound only for the fastest solidification rates. For 4.2 wt.% silicon content the MAD analysis pointed out that the tensile plastic behaviour and the microstructure integrity was in between the 3.5 and 4.5 wt.% silicon contents, representing a composition threshold where the reliable microstructures were only found with the fastest solidification rates, while considerable variability was found for the slowest ones. Support to the MAD analysis results was given from microstructure observations

The Correlation between Solidification Rates, Microstructure Integrity and Tensile Plastic Behaviour in 4.2 wt.% Silicon Strengthened Ductile Iron

High Silicon Strengthened Ductile Iron (HSiSDI) with 4.2 wt.% of silicon was produced in Y-blocks with different thicknesses to investigate the effects of the solidification rate on microstructure integrity and tensile mechanical properties. With decreasing solidification rates, the graphite degeneracy with the appearance of chunky graphite became more significant at the highest silicon contents, so chemical ordering and graphite degeneracy seemed to be qualitative explanations of tensile property degradation. However, a deeper analysis of the relationship between solidification rate, microstructure and tensile properties was realized through an innovative approach based on the Matrix Assessment Diagram (MAD), where the parameters of Voce equation resulting from best-fitting the experimental tensile flow curves of a significant number of HSiSDI samples, were plotted. For 3.5 wt.% silicon content, the MAD analysis indicated that the microstructure was sound for any solidification rate, while for 4.5 wt.% the microstructure was sound only for the fastest solidification rates. For 4.2 wt.% silicon content the MAD analysis pointed out that the tensile plastic behaviour and the microstructure integrity was in between the 3.5 and 4.5 wt.% silicon contents, representing a composition threshold where the reliable microstructures were only found with the fastest solidification rates, while considerable variability was found for the slowest ones. Support to the MAD analysis results was given from microstructure observations