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L'acciaio AISI 316L, sottoposto a kolsterizzazione mediante trattamento industriale, è stato esaminato mediante Spettroscopia Meccanica (S.M.) e nanoindentazione al fine di determinare il modulo elastico E dello strato indurito superficiale (fase S). I risultati di S.M. mostrano che il modulo elastico della fase S è 202 GPa, un valore moderatamente più alto di quello del materiale non trattato. Le prove di nanoindentazione, eseguite con carichi di 5, 15 e 30 mN, mostrano con il carico più basso, corrispondente ad una profondità di penetrazione di ~ 110 nm, un modulo di quasi 400 GPa; i valori di E poi rapidamente decrescono. Questi risultati unitamente a misure XPS (X-ray Photoelectron Spectroscopy) e AES (Auger Electron Spectroscopy) della concentrazione di C inducono a considerare l'ipotesi che i primi strati della superficie siano costituiti da una struttura diversa dalla fase S, cioè una struttura mista DLC (Diamond-like carbon) - taC (tetrahedral carbon).

Internal friction (IF) data show that the evolution of C-Cr n associate distribution of MANET steel is connected to the Cr-rich carbides (M 7 C 3 and M 23 C 6 ) precipitation. Carbides extracted from the matrix have been investigated by X-ray diffractometry and EDS microanalysis measurements. It is discussed the hypothesis that the M 7 C 3 carbides form by aggregation of C-Cr, associates.

This work deals with a non-destructive method for mechanical tests which is based on the indentation of materials at a constant rate by means of a cylinder with a small radius and penetrating flat surface. The load versus penetration depth curves obtained using this method have shown correspondences with those of tensile tests and have given indications about the mechanical properties on a reduced scale. In this work penetration tests have been carried out on various kinds of Cr martensitic steels (MANET-2, BATMAN and modified F82H) which are of interest for first wall and structural applications in future fusion reactors. The load versus penetration depth curves have been examined with reference to data obtained in tensile tests and to microhardness measurements. Penetration tests have been performed at various temperature (from −180 to 100°C). Conclusions, which can be drawn for the ductile to brittle transition, are discussed for MANET-2 steel. Preliminary results obtained on BATMAN and modified F82H steels are reported. The characteristics of the indenter imprints have been studied by scanning electron microscopy.

The internal friction spectrum of as-quenched MANET steel (10.5 Cr, 0.17 C, 0.003 N wt%) and its evolution following thermal treatments at increasing temperatures up to 773 K has been studied on the basis of the processes involving interactions between interstitial atoms (C and N) and substitutional Cr atoms in solid solution. The analysis of Q−1 curves shows that the successive stages of heat treatment cause complex redistributions of C atoms between interstices with a different number n of neighbour Cr atoms (0 ≤ n ≤ 6) and variations of the total amount of C in solid solution. The relaxation processes involving N have also been examined.

This work describes the anelastic and dynamic Young modulus behaviour of human dentin from room temperature up to 673 K. Human molars, extracted from individuals (males 55–70 years old) as part of their dental treatment, were cut to obtain bar-shaped samples subsequently used for mechanical spectroscopy experiments. In addition, thermo-gravimetric analysis (TGA) has been performed to assess a possible weight loss occurring in the same temperature range of mechanical spectroscopy tests. A broad and asymmetric internal friction (Q− 1) maximum at 500 K has been observed during the heating of the as-prepared samples. This maximum is absent during the following cooling down to room temperature. It is therefore due to the occurrence of an irreversible transformation in the sample. TGA shows a remarkable weight loss in the same temperature range. This effect has been related to loss of fluids and degradation of collagen. Another set of samples, previously kept for 36 h under a vacuum of 10− 2 Pa, were submitted at room temperature to test at increasing strain from 6 × 10− 6 to 7 × 10− 4. The results show transient and fully recoverable Q− 1 increase and dynamic modulus (E) decrease. The phenomenon has been ascribed to the breaking of weak H-bonds between polypeptide chains forming the triple-helix with consequent increase of the mean length of vibrating chain segments.

Liquid Pb–Bi eutectic alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system. The alloy has been characterized in liquid state from melting (125 °C) to 650 °C by mechanical spectroscopy. Experiments have been carried out using hollow reeds of austenitic stainless steel filled with the Pb-Bi alloy and sealed at the extremities. From 350 °C to 520 °C modulus shows a remarkable drop accompanied by a broad internal friction maximum. In the same temperature range radial distribution functions, determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The anelastic phenomena have been attributed to a structural re-arrangement of liquid metal. For comparison, other alloys of the Pb-Bi system with hypo-eutectic composition have been investigated.

Mechanical Spectroscopy provides information on microstructural features of materials not obtained by other techniques. In general, it is used for investigating physical phenomena, however it can be very useful also for solving problems related to industrial processes. This work describes and discusses some applications of metallurgical interest.

Austenitic stainless steels are characterized by good corrosion resistance in different environments, but their use is limited because of low hardness and poor wear resistance. Conventional thermochemical surface treatments for improving the mechanical strength of steels induce Cr carbide precipitation and thus are detrimental to corrosion resistance. A low-temperature (

The properties of Al–Li alloys have been extensively studied recently for structural applications in automotive and aerospace industry, thanks to their lower density and enhanced modulus of elasticity. In common with many Al alloys, one of the main issues is the loss of toughness and soundness of welded joints consequent upon welding operations, in particular, possible cracking in the weld metal and metallurgical modifications induced in the heat-affected zone. In this work, welding trials were carried out on 8090 Al–Li plates welded by electric arc, using a 5% Mg filler metal. Joints were mechanically and metallurgically characterized through tensile and microhardness tests, optical and scanning electron microscopy, and fractography on both welded and unwelded tensile specimens. Energy dispersive spectroscopy (EDS) measurements were also performed to evaluate chemical composition locally and determine the nature of precipitates.

Ni-based superalloys with biphasic structure (? + ?') are widely used for high-temperature applications, such as disks and blades of gas turbines and aeronautical engines. For these applications, the stability at high temperature is of utmost importance, in particular the coarsening and the morphological changes of ?' may be seriously detrimental for in-service components. Evolution of ?' particles strongly depends on the composition difference between disordered matrix and particles. The present work is devoted to the investigation of the ?' morphology and the microchemistry in single crystal CM186LC superalloy in as-received condition and after creep. The study was carried out by scanning electron microscopy and atomic force microscopy, standard X-ray photoelectron spectroscopy and scanning photoemission microscopy (SPEM) at the ELETTRA synchrotron facility in Trieste. The difference in the chemical composition of two phases, ? and ?', was revealed from the SPEM images and their spectral analysis. The structural evolution, taking place during creep and leading to rafting, seems to be determined not only by the external applied stress but also by W diffusion from ? to ?' phase.

This work describes the anelastic behavior of human dentin in the temperature range from 100 K to 673 K. Human molars, extracted from individual males (55-70 years old) as part of their dental treatment, were cut to obtain bar-shaped samples for mechanical spectroscopy (MS) experiments. The results are presents and discussed in two parts referring to experiments above and below room temperature.

By the use of suitable cylindrical indenters with flat surface and constant penetration rates, load versus penetration depth curves are obtained which show correspondence with the stress-strain curves of the tensile tests for some materials examined. After an initial linear stage, a limit load of σU is reached after which a stage of work-hardening occurs with a trend comparable to the one of the tensile test. The limit load σ U ⋟ 3σ y , σ y being the yielding load of the tensile test. For penetration rates = 100 μm/min, the loads of the work-hadening stage above σU tend to saturation values comparable to the loads of hardness only for some of the materials examined. With larger penetration rates, loads are reached well in excess above those of hardness. With metal-matrix composite alloys a stage with drops of load has been observed at the level of the loads of hardness. Besides those with constant penetration rates, tests with constant load have been also made on the same materials, with the results interpreted on the basis of the penetration rate effects.

The micro-analytical study of cellular precipitation in a high-nitrogen austenitic steel (HNS) was carried out by means of XPS, AES, photoelectron microscopy and EDS microanalysis. The use of photoelectron microscopy with high lateral resolution at the ESCA microscopy beamline of the Elettra synchrotron in Trieste permitted to determine the concentrations of N and Cr in the supersaturated matrix and inside the lamellae of the transformed zones. N in interstitial solution has a strong effect on solid solution strengthening, austenite stabilization and pitting corrosion resistance. Owing to their properties FINS can be used in different industrial fields, such as petrol plants, energy generation, production of paper and biomedicine. However, the precipitation of chromium nitrides, occurring in the temperature range of 550 - 1050 degrees C, can restrict the high-temperature applications of HNS. Cellular precipitation in the austenitic HNS after heat treatments has been already investigated by various techniques [1,2] and it was found that the transformation is accompanied by the modification of lattice parameter and micro-hardness. The results suggested that long-range diffusion of N from the untransformed gamma(s) matrix to the transformed regions may occur [2-4]. To complete the micro-structural study and verify if diffusion of N from gamma(s) matrix towards transformed regions really occurs, the experiments of AES and photoelectron microscopy have been carried out. This information was not available from the data of conventional XPS, where the diameter of investigated area is much higher than the inter-lamellar distance (about 250 nm) [1]. Moreover, internal friction (IF) and dynamic modulus measurements have been performed for investigating the distribution of N and other alloying elements on atomic scale. The examined HNS steel was prepared by Pressurized Electroslag Remelting; its nominal composition is reported in Tab. 1. The samples were isothermally heated at 850 degrees C in successive steps up to 23 hours. Auger spectra were collected by using an Escalab Mk 1I spectrometer (VG Scientific) equipped with 5-channeltron detection system and electron gun LEG 200, operated at 10 keV and 1-10 nA beam current. The spectra were acquired in the constant retard ratio (1 : 2) mode. The photoemission measurements with high lateral resolution were performed by means of the Scanning Photoelectron Microscopy (SPEM) at the Elettra synchrotron. The SPEM can be operated in imaging and spectroscopic modes with a spatial resolution of about 150 nm and resolution in energy of 0.2 eV, respectively. More experimental details on this technique have been reported previously [5,6]. IF and elastic modulus measurements were carried out by means of the VRA 1604 analyzer [7] on the reeds of 13.4 mm x 6.0 mm x 0.26 mm. The samples have been heated up to 800 degrees C at constant rate of 1.7 x 10(-2) degrees C s(-1). The modulus was determined from the resonance frequency f (Eq. 1) being m a constant, L and h length and thickness of the vibrating reed, rho material density.

In questa rassegna vengono presentati e discussi i risultati degli studi condotti dagli autori negli ultimianni riguardo la produzione e caratterizzazione di materiali metallici porosi. Dopo le prime esperienzenella produzione di schiume di Al a porosità chiusa, partendo da polveri e con l’aggiunta di TiH2 comeagente soffiante, si è passati alla produzione di schiume di diversi metalli a porosità aperta mediante latecnica “SDP” (sintering and dissolution process) modificata. Un’altra via percorsa per la produzione dischiume a basso costo è la cosiddetta “RP” (replication process), anch’essa sottoposta ad alcune variantirispetto alla tecnica classica a seconda del metallo o della lega che si intende schiumare. Un importanteaspetto di questo filone di ricerca ha riguardato la produzione di schiume partendo da materiale diriciclo, truciolo tal quale per quanto riguarda Al e sue leghe, griglie e pasta recuperate da batterie esausteper le schiume di piombo. Questa rappresenta un’interessante prospettiva, anche sotto il profilo energeticoe ambientale, per la conversione diretta del materiale, prodotto di scarto di lavorazioni, in schiume di Al ePb rispettivamente. Vengono quindi presentati i risultati sperimentali e le problematiche emerse durante ilprocesso di ottenimento della schiuma utilizzando il materiale recuperato. Un ulteriore aspetto hariguardato la produzione di schiume di Fe che combinano un buon mix tra proprietà meccaniche erequisiti di leggerezza. Infine l’ultimo punto della rassegna illustra i principali risultati della ricerca piùrecente che riguarda la produzione di elettrodi porosi realizzati in schiume di Pb. Una possibileapplicazione potrebbe essere la realizzazione di lamierini in piombo da impiegare come elettrodimicroporosi in accumulatori al piombo acido con l’obiettivo di ridurne il peso e migliorarne le prestazioni.Critico da questo punto di vista si presenta il problema del controllo della dimensione della porosità. Atale proposito alcune problematiche devono ancora essere superate e sono tuttora oggetto disperimentazione. Per tutte le tipologie di schiume prodotte è stata effettuata una caratterizzazionemorfologica e meccanica.

Il presente lavoro ha per scopo la caratterizzazione microstrutturale di giunti saldati mediante Friction StirSpot Welding (FSSW), realizzati in lega d’alluminio 6082. Viene inoltre prospettata una modalità dimodellazione dei medesimi che consenta la valutazione delle loro grandezze ingegneristicamente piùsignificative. La struttura dei giunti è esaminata con osservazioni di microscopia ottica, microscopiaelettronica in trasmissione, diffrazione dei raggi X (XRD) e viene confrontata con quella del materiale talquale. La zona deformata è anche caratterizzata con prove di indentazione strumentata FIMEC e viene svoltauna caratterizzazione a rigidezza su provini Tensile-Shear aventi un’unica giunzione FSSW.Utilizzando i dati derivanti da tutti i rilievi sperimentali descritti, viene svolta una indagine sistematica ondevalutare l’influenza che i parametri di saldatura hanno sulla variazione locale delle caratteristichemeccaniche del materiale. La modellazione FE di riferimento, basata sullo sviluppo di complessi modelli adelevata parametricità, tiene conto di tutti le variabili geometriche e tecnologiche nonché della differenziazionedelle zone termicamente e termomeccanicamente alterate; attese queste caratteristiche, essa consente divalutare, in maniera accurata, l’effetto strutturale che ne consegue.

Il presente lavoro è finalizzato alla sperimentazione di un processo di saldatura al fascio laser, mediantepassata unica, di lamiere di acciai placcati con leghe a base di Ni (Alloy 59 e lega Monel 400).La particolarità del procedimento di saldatura al fascio laser in una sola passata consiste nell’assenza dilembi di cianfrinatura e nell’impiego, come materiale d’apporto, di inserti consumabili in lega di Nichelposti tra le lamiere da saldare. La possibilità di ottenere giunti saldati di buona qualità ed esenti dadifetti viene verificata attraverso osservazioni macrografiche ed esami metallografici. Le sezioni saldatesono studiate mediante osservazioni di microscopia ottica ed elettronica in scansione (SEM), misuremicroanalitiche con spettroscopia in dispersione di energia (EDS) e prove di microdurezza Vickers.

Corrosion, wear or the combined effects of these failure modes cost the industrial economies hundreds of billions of euros each year. One of the more effective ways to reduce damage due to corrosion and wear is to treat, or “engineer” the surface, so that it can perform functions that are distinct from those required by most materials. For example, steel is a very popular material, because it is inexpensive, strong and easily manufactured. Unfortunately, it is highly susceptible to corrosion in many environments and therefore needs to be coated in order to achieve a satisfactory life service. Small components can be painted, aluminized, electroplated, or clad with more corrosion resistant materials. For parts that also require wear strength, they can be thermally sprayed or coated with thin-films. Finally, when dealing with large components, the size, weight, and handling problems may limit the type of surface treatment to be considered. The aim of the research work presented in this PhD thesis was to study the interactions between the metal/ceramic and metal/metal coupling surfaces to improve the wear resistance of the materials in sliding motion. Most of my research work is included here as a collection of three papers submitted in the same format they were published or in a preprint version. Each paper is an individual piece of work with separate sections including: abstract, introduction, materials and experimental details, results and discussion, conclusions, and references. A failure analysis study was carried out on some specific mechanical components of diesel engines for industrial application. In order to increase the wear resistance of rocker arms, pushrods and valves, the deposition of ceramic coatings thermally sprayed was considered. Wear tests were performed on a plasma-sprayed ceramic coating in sliding motion against steel in order to understand the effect of a normal load applied, as well as the environmental conditions on the metal/ceramic coupling. Moreover, the influence of relative humidity on the tribological behaviour of two types of plasma-sprayed ceramic coatings and two types of HVOF-sprayed cermets in sliding motion against alumina, was evaluated through pin-on-disk testing. Different techniques for the microstructural examination were employed in this research study: Optical Microscopes (OM) and Scanning Electron Microscopes (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) microprobe were used and also X-ray Diffraction (XRD) was carried out to describe the morphology of worn surfaces and to identify the main wear mechanisms involved. In addition, surface roughness, Vickers microhardness and fracture toughness measurements were performed in order to characterise the materials subjected to wear testing.