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Laser-based Powder Bed Fusion (L-PBF) technology is one of the most commonly used metal Additive Manufacturing (AM) techniques to produce highly customized and value-added parts. The AlSi10Mg alloy has received more attention in the L-PBF process due to its good printability, high strength/weight ratio, corrosion resistance, and relatively low cost. However, a deep understanding of the effect of heat treatments on this alloy's metastable microstructure is still required for developing tailored heat treatments for the L-PBF AlSi10Mg alloy to overcome the limits of the as-built condition. Several authors have already investigated the effects of conventional heat treatment on the microstructure and mechanical behavior of the L-PBF AlSi10Mg alloy but often overlooked the peculiarities of the starting supersatured and ultrafine microstructure induced by rapid solidification. For this reason, the effects of innovative T6 heat treatment (T6R) on the microstructure and mechanical behavior of the L-PBF AlSi10Mg alloy were assessed. The short solution soaking time (10 min) and the relatively low temperature (510 °C) reduced the typical porosity growth at high temperatures and led to a homogeneous distribution of fine globular Si particles in the Al matrix. In addition, it increased the amount of Mg and Si in the solid solution available for precipitation hardening during the aging step. The mechanical (at room temperature and 200 °C) and tribological properties of the T6R alloy were evaluated and compared with other solutions, especially with an optimized direct-aged alloy (T5 alloy). Results showed that the innovative T6R alloy exhibits the best mechanical trade-off between strength and ductility, the highest fatigue strength among the analyzed conditions, and interesting tribological behavior. Furthermore, the high-temperature mechanical performances of the heat-treated L-PBF AlSi10Mg alloy make it suitable for structural components operating in mild service conditions at 200 °C.

The research activity carried out in the Brasimone Research Center of ENEA concerns the development and mechanical characterization of steels conceived as structural materials for future fission reactors (Heavy Liquid Metal IV Generation reactors: MYRRHA and ALFRED) and for the future fusion reactor DEMO. Within this framework, two parallel lines of research have been carried out: (i) characterization in liquid lead of steels and weldings for the components of the IV Generation fission reactors (GIV) by means of creep and SSRT (Slow Strain Rate Tensile) tests; (ii) development and screening on mechanical properties of RAFM (Reduced Activation Ferritic Martensitic) steels to be employed as structural materials of the future DEMO fusion reactor. The doctoral work represents therefore a comprehensive report of the research carried out on nuclear materials both from the point of view of the qualification of existing (commercial) materials for their application in the typical environmental conditions of 4th generation fission reactors operating with lead as coolant, and from the point of view of the metallurgical study (with annexed microstructural and mechanical characterization of the selected compositions / Thermo Mechanical Treatment (TMT) options) of new compositional variants to be proposed for the “Breeding Blanket” of the future DEMO Fusion Reactor.

In the most recent years, Additive Manufacturing (AM) has drawn the attention of both academic research and industry, as it might deeply change and improve several industrial sectors. From the material point of view, AM results in a peculiar microstructure that strictly depends on the conditions of the additive process and directly affects mechanical properties. The present PhD research project aimed at investigating the process-microstructure-properties relationship of additively manufactured metal components. Two technologies belonging to the AM family were considered: Laser-based Powder Bed Fusion (LPBF) and Wire-and-Arc Additive Manufacturing (WAAM). The experimental activity was carried out on different metals of industrial interest: a CoCrMo biomedical alloy and an AlSi7Mg0.6 alloy processed by LPBF, an AlMg4.5Mn alloy and an AISI 304L austenitic stainless steel processed by WAAM. In case of LPBF, great attention was paid to the influence that feedstock material and process parameters exert on hardness, morphological and microstructural features of the produced samples. The analyses, targeted at minimizing microstructural defects, lead to process optimization. For heat-treatable LPBF alloys, innovative post-process heat treatments, tailored on the peculiar hierarchical microstructure induced by LPBF, were developed and deeply investigated. Main mechanical properties of as-built and heat-treated alloys were assessed and they were well-correlated to the specific LPBF microstructure. Results showed that, if properly optimized, samples exhibit a good trade-off between strength and ductility yet in the as-built condition. However, tailored heat treatments succeeded in improving the overall performance of the LPBF alloys. Characterization of WAAM alloys, instead, evidenced the microstructural and mechanical anisotropy typical of AM metals. Experiments revealed also an outstanding anisotropy in the elastic modulus of the austenitic stainless-steel that, along with other mechanical properties, was explained on the basis of microstructural analyses.

L’attività svolta durante il dottorato è stata incentrata su due tematiche riguardanti: (i) la modifica della composizione chimica delle classiche leghe di alluminio da fonderia per incrementarne la resistenza e stabilità termica; (ii) lo studio del comportamento a fatica di acciai innovativi alto-resistenziali, allo scopo di valutarne il loro utilizzo per la produzione di alberi motore e distribuzione in sostituzione dei tradizionali acciai utilizzati dopo bonifica e trattamento superficiale di nitrurazione. La messa a punto di una lega di alluminio da fonderia con elevata resistenza in temperatura ha richiesto, oltre all’individuazione della composizione chimica, l’ottimizzazione del trattamento termico e una completa caratterizzazione meccanica statica a fatica sia a temperatura ambiente sia a 200°C. L’attività ha permesso di sviluppare una lega, ottenuta aggiungendo 1,3% in peso di rame alla classica lega A357 (Al-Si-Mg), cha ha mostrato avere proprietà meccaniche superiori a quelle delle tradizionali leghe Al-Si-Mg-Cu quali la A354 e C355 sia a temperatura ambiente che a 200 °C dopo lunga esposizione in temperatura. Per quanto riguarda gli acciai innovativi, dopo una preliminare analisi di mercato per individuare quali acciai potessero essere oggetto di studio, è stato valutato come migliorarne le prestazioni a fatica, anche in presenza d’intaglio, attraverso la scelta del trattamento termico più opportuno e del processo di pallinatura. I risultati delle caratterizzazioni microstrutturale e meccanica svolte hanno permesso di individuare due acciai (nomi commerciali K890 e ASP2017) ottenuti per metallurgia delle polveri, ad oggi utilizzati solo per la produzione di stampi e/o utensili, in grado di sostituire gli acciai con cui vengono oggi realizzati i componenti, senza la necessità di eseguire il trattamento di nitrurazione, Two main research activities were addressed during this PhD year, namely: 1. Evaluation of fatigue behavior of shot peened hot work tool steels in notched conditions; 2. Study of the effect of the Cu addition to Al-Si-Mg casting alloys. The activities on hot work tool steels, obtained by powder metallurgy and ESR technologies, were focused on the evaluation of their notched fatigue behavior. The shoot peening process was also applied. The role of shoot peening in terms of residual stresses and hardness, as well as the effect of inclusions size on their fatigue behaviour was investigated. Rotating bending fatigue tests showed an increase of the fatigue resistance of notched samples, as a result of shot peening, of about 20-40%. The aim of the activity on Al-Si-Mg casting alloy was to evaluate the effect of Cu addition on its mechanical performance, mainly in terms of tensile and fatigue strength, at both room temperature and 200 °C, in peak aged and overaged conditions. The results indicate that the addition of Cu to the A357 alloy enables to maintain, in the tested overaged conditions, hardness values higher than 100 HB, and at 200°C UTS and YS values close to 210 and 200 MPa, respectively, and fatigue strength of about 100 MPa. The mechanical behaviour of the new alloy was comparable to that of commercial quaternary alloys Al-Cu-Si-Mg, such as C355.

The European Union has undertaken several efforts to reduce the non-exhaust particulate matter emissions from road vehicles. One of the major sources of these emissions is the wear of brake pads and discs. The experimental work presented in this thesis has been performed within the European project called LOWBRASYS that aims at reducing the particulate matter emissions due to the wear of the components of braking systems. Different strategies have been identified for reaching this aim but the present work focuses on the investigation of the wear mechanisms at the disc-pad interface and on their role on the emission in the atmosphere and in the environment of wear debris. In order to achieve the reduction in the particulate matter emissions, the traditional gray cast iron discs have been coated with different cermet coatings deposited via high velocity oxygen fuel (HVOF) process. A further attempt for improving the wear resistance of the gray cast iron discs was performed by applying on them an industrial heat treatment. The cermet coatings have been widely employed in the field of the oil and gas industry for improving the wear resistance and the service life of valves and pipes but their use in the field of road-vehicles-braking-systems has never been explored so far. The present work focuses on the tribological characterization of HVOF coated and heat treated discs performed by means of laboratory-scale-pin-on-disc tribometers at both room and high temperatures (300°C). The sliding speed of 1.57 m/s and the nominal contact pressure of 1 MPa used for this characterization have been selected in order to replicate the actual contact conditions between brake pads and brake discs during an urban cycle braking action. Since the use of lab-scale experimental apparatuses, these tests have not been meant to reproduce real braking conditions for which specific dyno bench tests have been performed in further characterization tests. The pins used during the PoD characterization, made of three different commercially-available friction materials, had dimensions of 12 mm in height and 6 and 10 mm in diameter. The discs, 6 mm in thickness and 58.9 mm in diameter, were coated with a 70 µm thick layer of cermet materials. The heat treated discs had the same dimensions of the coated ones. The tested specimens have been machined from the real braking components, the pins have been extracted from the brake pads while the discs from the braking tracks of the rotors. Since the novelty of the application of the HVOF coatings in the field of braking systems, two preliminary studies of the surface parameters of the coated discs and of the running-in of the pin-disc system have been performed. The first one was conducted on WC-CoCr coated discs polished with different intensities in order to achieve four different average surface roughnesses: 5, 1, 0.1, 0.04 µm respectively. The results of the study highlighted that the wear of the friction material decreased by four order of magnitude by passing from an average surface roughness equal to 5 µm to 0.04 µm. The friction coefficient followed the opposite trend passing from 0.3 for the 5 µm rough coating to 0.7 for the 0.04 µm. The SEM observation of the wear tracks on the discs revealed a high material transfer from the pins in the case of the 5 µm rough coatings due to the abrasive interaction exerted by the hard coating asperities on the relatively soft friction material. The compactness of the material transferred onto the disc surface increased as the average surface roughness of the coating decreased leading to the formation of contact patches also on the coated disc surfaces. From the profilometric analysis of the worn disc their wear resulted negligible. The EDXS analysis of the secondary plateaus of pins detected an increasingly concentration of tungsten and cobalt with the decrease in the surface roughness of the coating meaning that, although the wear of the coating could not be detected from the profilometer, some minor transfer of material occurred during the sliding action. From all the considerations mentioned above the most promising surface roughness, in terms of frictional performances and industrial feasibility, was equal to 1 µm. The second study aimed at the investigation of the running-in stage of the WC-CoCr and Cr3C2-NiCr coated discs in the as-sprayed (Ra ≈ 5 µm) and polished conditions (Ra ≈ 1 µm). From this former investigation the polishing procedure of the coated discs was found fundamental in order to reach the best frictional and wear performances; the spontaneous surface modifications occurring during pin-on-disc tests were not as efficient as the controlled polishing procedure in reducing the surface parameters of the coated discs and so in improving their performances. On the basis of the results of the two former studies presented above, the tribological characterization at both room and high temperature (300°C) of the WC-CoCr, Cr3C2-NiCr, WC-Cr3C2-CoCr, WC-FeCrAlY coated discs and of the heat treated one was performed on specimens with an average surface roughness at around 1 µm. Three different friction material formulations were used in order to optimize their frictional and wear performances with the disc counterface. In all cases the EDXS analysis detected the presence of the coating elements, i.e. tungsten, cobalt and nickel, inside the secondary plateaus of the friction material. Depending on the abrasive content of the friction materials and on the testing temperature the amount of the transferred elements varied, i.e. a low amount of abrasives and a high testing temperature gave rise to a reduction in the elements transferred on the pin surfaces. The best tribological combination was the coupling between the friction material FMB, i.e. the one with the lowest amount of abrasives, and the WC-FeCrAlY coated disc. The results attained with the pin-on-disc tribological characterization of the friction materials were validated during full-scale dyno bench tests. These tests were performed on the most promising materials and they had a twofold aim: as mentioned above they were used to validate the results of the tribometer tests and to collect the particulate matter emitted during braking. The analysis of the wear debris highlighted that, in the case of the friction material FM4 slid against the WC-CoCr coated disc, some cobalt was present. From the deeper analysis of the debris resulted that traces of tungsten and cobalt were found only in the coarser fraction of wear debris, collected on the PM1 filter. The coupled SEM+EDXS analysis of the finer particulate matter, with an average aerodynamic diameter varying from 0.25 to 0.054 µm, did not detected the presence of the coating elements. This was consistent with the observations of the PM1 wear debris that identified WC particles with dimensions comparable to that of the initial carbide particle size inside the coatings; the wear mechanism of the coatings seemed to be the carbide pullout from the metallic matrix without the further fragmentation of the particles due to sliding. Nevertheless, during one of the TEM observation of the particles with an average aerodynamic diameter of 0.094 µm the SAED analysis detected the presence of W2C. On the basis of this last observation and considering that the presence of cobalt inside the finest fraction of debris could not be completely disregarded since it could remain stuck on the W2C particles, the selected coating material for the application in braking systems was the WC-FeCrAlY. This conclusion was consistent with the frictional and wear data attained from the PoD tribological characterization that identified the FMB friction material and the WC-FeCrAlY coated discs as the best coupling in terms of frictional and wear behavior. The study of the thermal behavior of the novel developed braking materials during a pin-on-disc room temperature test was performed by means of a finite element simulation based on the perfect contact approach. The heat flux applied as the thermal input of the model was calculated from the experimental data acquired during the tests. The calibration of the boundary conditions was performed by comparing the experimental curves of the temperatures acquired during the tests with the temperature curves calculated from the FE analysis. The results of the simulations showed that the temperature field during the pin-on-disc tests was influenced from both the friction coefficient and from the thermal properties of the coated discs, i.e. the lower thermal conductivity of the coatings gave rise to a higher average contact temperature with respect the uncoated cast iron discs. The results of FE analysis were then used to propose an analytical relationship that could be used for describing the raise in temperature during a pin-on-disc test without performing further thermal simulations.

Rheocasting process integrated with the high pressure die casting method (Rheo-HPDC) has established itself as a new promising technology to produce high-quality components. However, different types of microstructural segregation induced by the semi-solid process influence the properties of the final component. The semi-solid microstructural features and the new compositions require detailed corrosion studies and verification. The first part of this thesis deals with microstructural and corrosion studies of the conventional and Rheo-HPDC Al-Si alloys. In this part, corrosion properties of two Al–Si alloys containing 2.5 and 4.5 wt % silicon cast by Rheo-HPDC method were examined in the diluted Harrison solution using polarization and electrochemical impedance spectroscopy (EIS) techniques on as-cast and ground surfaces. The microstructural studies revealed that samples taken from different positions (with respect to the feeding gate) contain different fractions of solid and liquid parts of the initial slurry. It was shown that the Rheo-HPDC Al-Si alloys are prone to the localized form of corrosion inside the eutectic region at the interface of aluminum with silicon phase and intermetallic particles. Electrochemical behavior of as-cast, ground surface, and bulk material was shown to be different due to the presence of a segregated skin layer and the surface quality. Corrosion properties of the two Al-Si alloys cast by the conventional and Rheo-HPDC process were also evaluated and compared in 0.01, 0.05, 0.1 and 0.6 M NaCl solutions. The conventional HPDC and semi-solid alloys presented similar EIS responses. However, the semi-solid samples with a lower fraction of the eutectic phase showed slightly higher impedance values in the more diluted sodium chloride solutions. Corrosion morphological features, including localized corrosion, trenching and co-operative corrosion rings were comparable for both types of alloys. However, in the anodic polarization test, the semi-solid alloys presented a higher resistance to pitting corrosion. To protect aluminum alloys from corrosion, chromium-based conversion coating has been successfully used for decades, due to its extensive protection. However, rising concerns and new restrictions on the environmental hazards of Cr (VI) compounds have led to intensive efforts to develop alternative coatings. The second and third parts of this thesis address the effort to investigate two alternatives in this field. Cerium-based conversion coatings were deposited on the conventional and Rheo-HPDC Al-Si alloys by immersion in cerium nitrate aqueous solutions. Different parameters were studied to optimize the conversion coating, and NaCl or H2O2 were also added to the solution to modify or accelerate the deposition process. The results revealed that applying cerium-based conversion coating on Al-Si alloys, is possible and a selective deposition is obtained due to the presence of iron-rich intermetallic particles inside the eutectic region. Under the accelerated conditions, the deposition mechanism includes dissolution of the aluminum matrix, selective dissolution of aluminum from the noble intermetallic particles, oxidation of iron from these particles, and the deposition of cerium hydroxide/oxide layer. The results revealed that the improvement in corrosion resistance in the presence of selectively deposited cerium-based conversion coating is more significant compared to the homogenous coating obtained from the conversion solution containing H2O2. The aluminum alloy with a higher amount of silicon showed more active surface during the conversion process which reduces the required concentration of Ce(NO3)3 but also makes it difficult to work with more aggressive solutions. In the third part of this thesis, the possible protective effect of polypyrrole coating on pure aluminum and Rheo-HPDC Al-Si alloys was investigated. Different electropolymerization solutions containing the Py monomer, SDS, DHBDS (Tiron), C6H8O7 and NaNO3 were used. The presence of nitrate anions led to the passivation of the aluminum electrode (both pure and alloy) during the electropolymerization and to the deposition of a thicker/more conductive coating. These facts resulted in longer and more efficient corrosion protection in NaCl solutions. This polypyrrole coating was able to keep the alloys’ surface potential noble for at least 168 hours. Which can be attributed to the anodic protection provided by the reduction of the polymer. It was shown that the presence of silicon phase or intermetallic particles has a positive effect on the electropolymerization of polypyrrole film. Therefore, the coatings deposited on the alloys possess higher thicknesses compared to those deposited on the pure aluminum. In the presence of chloride ions, all coatings suffered from the formation of blisters as a result of severe (localized) galvanic interaction of polypyrrole with aluminum. This may question the application of polypyrrole coating in concentrated NaCl solutions. However, it is shown that the protection efficiency can be improved by altering the solution chemistry which affects the polymer/metal interface and the conductivity and the barrier properties of the coating. Therefore, the application of polypyrrole in corrosion protection is not totally ruled out but needs specific considerations.

The increasingly strict regulations on greenhouse gas emissions make the fuel economy a pressing factor for automotive manufacturers. Lightweighting and engine downsizing are two strategies pursued to achieve the target. In this context, materials play a key role since these limit the engine efficiency and components weight, due to their acceptable thermo-mechanical loads. Piston is one of the most stressed engine components and it is traditionally made of Al alloys, whose weakness is to maintain adequate mechanical properties at high temperature due to overaging and softening. The enhancement in strength-to-weight ratio at high temperature of Al alloys had been investigated through two approaches: increase of strength at high temperature or reduction of the alloy density. Several conventional and high performance Al-Si and Al-Cu alloys have been characterized from a microstructural and mechanical point of view, investigating the effects of chemical composition, addition of transition elements and heat treatment optimization, in the specific temperature range for pistons operations. Among the Al-Cu alloys, the research outlines the potentialities of two innovative Al-Cu-Li(-Ag) alloys, typically adopted for structural aerospace components. Moreover, due to the increased probability of abnormal combustions in high performance spark-ignition engines, the second part of the dissertation deals with the study of knocking damages on Al pistons. Thanks to the cooperation with Ferrari S.p.A. and Fluid Machinery Research Group - Unibo, several bench tests have been carried out under controlled knocking conditions. Knocking damage mechanisms were investigated through failure analyses techniques, starting from visual analysis up to detailed SEM investigations. These activities allowed to relate piston knocking damage to engine parameters, with the final aim to develop an on-board knocking controller able to increase engine efficiency, without compromising engine functionality. Finally, attempts have been made to quantify the knock-induced damages, to provide a numerical relation with engine working conditions.

The demand for ductile cast iron components, with weights ranging from a few kilograms to several tons, has increased significantly in recent years, both for technical and economic reasons. In fact, the lower cost compared to other materials, the good castability, which allows to obtain near-net shape components in as-cast conditions, and the mechanical properties that can be obtained, are just some of the motivations that attract mechanical designers. In the case of large components, the knowledge of mechanical behaviour is however limited and incomplete. What is known is that, by increasing the thicknesses of the castings, the solidification times increase and the cooling rates are greatly reduced. In these critical conditions, solidification can lead to the formation of microstructural defects, sometimes unavoidable, which negatively influence the local mechanical properties of ductile cast iron components. From an initial and in-depth bibliographic analysis, it emerged that, in literature, these issues have been studied in a systematic way only in the recent years. As a result, the number of data available for engineers is limited and it can be noted that there are many lacks, especially with regard to the mechanical characterization and fatigue behaviour of these materials. Specifically, most of the work has been carried out considering traditional ferritic ductile iron used, for example, in the production of wind turbine components. In some studies, traditional cast irons with pearlitic matrix have been characterized, while the data concerning the mechanical and microstructural properties of new-generation cast irons with a solid solution strengthened ferritic matrix are very limited. The First Chapter contains a brief introduction concerning the above mentioned topics, with particular attention to the state of the art and to the recent works published in the literature The Second Chapter describes the experimental campaign conducted during the doctorate, following which an in-depth microstructural and mechanical characterization of different types of spheroidal cast iron characterized by different conditions of cooling and solidification was carried out. During the experimental campaigns, microstructural analyses were performed using an optical microscope and image analysis software on polished and etched samples. In addition, tensile and fatigue tests were performed on specimens obtained from the areas of interest within the castings. The fracture surfaces were then analysed by SEM to identify the causes of fracture. In the Third Chapter the most significant experimental results obtained from the microstructural and mechanical characterization of a traditional ferritic matrix iron are reported. The aim is to expand the literature with further experimental data on this type of material in specific cooling and solidification conditions. In the Fourth Chapter, because of the few works in the literature, cast iron with pearlitic matrix was studied. In particular, through the realization of three experiments, the effect that the post-inoculation process have on the microstructural parameters and on the mechanical properties has been investigated. In the Fifth Chapter, the results obtained on new-generation solution strengthened ferritic ductile irons are reported. In particular, the effect of different amount of silicon and antimony on the properties of castings characterized by long solidification times has been investigated. In the Sixth Chapter, the microstructural, mechanical and fatigue properties of a particular grade of solution strengthened ferritic ductile iron have been evaluated as a function of different section thicknesses and solidification times. In the Seventh Chapter, a model that allows estimating the fatigue strength of as-cast ductile irons containing solidification defects is proposed based on the new experimental data. The Eighth Chapter presents concluding remarks on the work in order to discuss the main results

Cemented carbides are composite materials formed by high amount of WC bonded by a soft phase, usually Co. They are used in many applications, such as drawing dies, cutting tools and hot rolls due to theirs remarkable properties of high hardness and wear resistance. Mechanical properties are strongly related to microstructure, namely the binder amount and the carbide grain size. Increasing the binder content and the carbide grain size, the hardness decreases ad the fracture toughness increases. In this PhD, the correlations between the mechanical properties of WC-Co and the microstructural characteristics, in parts taken from industrial production, were defined. After that, the influence of the residual microporosity on the mechanical properties was evaluated. Considering the production process, another important modification of the final microstructure of WC-Co occurs due to the liquid cobalt migration phenomenon. Based on this, also the liquid cobalt migration that occurs during sintering was investigated. At the end of the thesis, since a few data are available in literature, Thermal Fatigue and oxidation damage in WC-Co were studied. The main results of this PhD thesis show that the hardness and fracture toughness of WC-Co are defined by the mean binder free path and not by the contiguity since the high standard deviations, the microstructural fineness and also the high carbide grain size scatter. Differently, in case of mechanical strength, also the residual microporosity that depends on the dewaxing stage must be defined. Furthermore, the dewaxing stage acts on the liquid cobalt migration that affects the surface properties and also the final microstructure of the WC-Co part in industrial production. At the end, considering the damages that occur during high temperature applications, the TF and oxidation resistance of WC-Co results affected by the Co content: high cobalt content leads to a better condition of TF damage and s higher oxidation resistance.

The contact fatigue and surface damage of prealloyed (Fe-0.85Mo, Fe-1.5Mo) and diffusion bonded (Ni-free, low-Ni, high-Ni) powder metallurgy (PM) steels were investigated. Materials subjected to contact stress fail due to the nucleation of subsurface cracks (contact fatigue cracks), nucleation of brittle surface cracks, and surface plastic deformation. The occurrence of these contact damage mechanisms was predicted using theoretical models, which were developed by assuming that crack nucleation is preceded either by local plastic deformation (contact fatigue and surface plastic deformation) or local brittleness (brittle surface cracks ) of the metallic matrix. With reference to the mean yield strength of the matrix (mean approach) or the yield strength of soft constituents (local approach), the models predict the theoretical resistance of materials to the formation of damage mechanisms. The models were then verified using experimental evidence from lubricated rolling-sliding contact tests. In addition, the effect of compact density and microstructures of materials on the resistance to contact damage mechanisms was investigated. Density and microstructure were modified by varying green density, alloying elements, sintering temperature and time, and applying strengthening treatments: carburizing and shot peening on prealloyed (homogenous microstructure) and carburizing, sinterhardening and through hardening on diffusion bonded (heterogeneous microstructure) steels. The theoretical resistance to subsurface and surface crack nucleation in prealloyed materials was predicted using the mean approach since the microstructure is homogeneous. But the local approach is applied for diffusion bonded materials (Ni-free and low-Ni); exceptionally, the mean approach was applied for some homogeneous microstructure of Ni-free material sintered at a prolonged time. However, the models have a limitation in predicting the contact damage mechanisms in a high-Ni material. This issue may require further investigation to modify the model. Shot peening provides higher resistance to the nucleation of surface cracks. High compact density, high sintering temperature and time, and sinterhardening improve the resistance to contact damage mechanisms for Ni-free and low-Ni materials.

Ultrafine grained (~ 1μm) steels have been the subject of extensive research work during the past years. These steels generally offer interesting perspectives looking for improved mechanical properties. UFG Powder Metallurgy hot work tool steels (HWTS) can be fabricated by high energy mechanical milling (MM) followed by spark plasma sintering (SPS). However, similarly to most UFG and Nano-Crystalline (NC) metals, reduced ductility and toughness result from the early plastic instabilities in these steels. Industrialization of UFG PM Tool Steels requires the application of specific metallurgical tailoring to produce tools with sound mechanical properties or in a more optimistic way, to break the Strength-Toughness “trade-off” in these materials. Among the possible ways proposed to restore ductility and toughness without losing the high strength, “Harmonic microstructure” design seems to be a very promising endeavor in this regard. Harmonic microstructure materials consist of a tunable volume fraction of evenly spaced “isolated” coarse-grained particles (CG) surrounded by a 3D interconnected network of UFG particles. CGs provide ductility and toughness, while high strength is guaranteed by the interconnected network of UFGs. This peculiar design offers an extra work hardening due to the generation of geometrically necessary dislocations at the interfaces of UFGs and confined CGs that are essentially present to accommodate the strain gradient imposed by the inhomogeneous (bimodal grained) microstructure. The first part of this work is devoted to the development of PM tool steels with harmonic microstructure. Due to the difficulties of processing hard tool steel particles according to the methods reported in the literature, an economical, simple alternative approach is also proposed. Near full density “Harmonic structure“ AISI H13 samples were produced using different volume fractions of UFG/NC mechanically milled (MM) and CG as-atomized particles followed by short time (30 min) low-temperature (1100°C) SPS. A combination of high hardness and significantly improved fracture toughness was achieved for the blends containing more that 50% UFG particles. The optimized mechanical properties was achieved by the mixture of 60% UFG particles where the sample showed a hardness near to the value predicted by the rule of mixtures (i.e. 405 HV10 vs. 406 HV10) while apparent fracture toughness (Kapp) was about 10% higher than that of predicted by the same rule (i.e. 52.0 MPa*m1/2 vs. ~47.0 MPa*m1/2). A toughening effect was evidenced for the samples essentially showing harmonic microstructure. Toughening was interpreted to be the result of the deviatory effect of coarse-grained round atomized particles together with energy dissipation by decohesion at the CG/UFG or UFG/UFG interfaces leading to a local drop of the driving force for the crack propagation. The design allowed to easily adjust the strength and toughness to meet the specific application-oriented requirements. The harmonic steel was also subjected to Thermal Fatigue (TF) testing. The preliminary results confirmed that this microstructure combined the beneficial effects of both of its constituents, i.e., the low crack nucleation rate of CG H13 and the low crack propagation rate of UFG H13, thus showing the lowest pyrocracking factor. Moreover, TF crack deflection as an extrinsic toughening mechanism was evidenced in Harmonic Microstructure. The second part of this work deals with the production and characterization of a PM HWTS reinforced with partially stabilized zirconia (PSZ). HWTS composites show improved hardness and remarkable wear resistance but generally also a systematic lower fracture toughness than the base material. Deteriorated toughness in metal matrix composites (MMCs) with a high strength matrix is mainly interpreted as a result of early damage initiation at the hard particles (HPs) or Matrix-HP interface. This damage can be even anticipated in the presence of readily damaged HPs (i.e. processing related flaws). Selection of PSZ as reinforcement was aimed at improving the strength and fracture toughness of the composite by taking advantage of the transformation toughening effect of PSZ. Two different types of PSZ, different volume fractions (10 and 20 vol. %) and sizes of reinforcement were used. Mechanical Alloying (MA) was used to process the composite powders to refine the matrix microstructure and both the matrix and PSZ particle size hence increasing the strength of the PSZ particles according to the Griffith strength formalism, and also to overcome the aggregation problems. Powders were consolidated by (SPS). The influence of processing parameters on density and microstructure was investigated. Short time (30 min) low-temperature (1100°C) consolidation by SPS allowed preserving the refined microstructure while achieving a maximum relative density of 98.6%. Moreover, short time sintering did not allow the extensive formation of thermodynamically plausible reaction products at the PSZ-H13 interface. As a result of dispersion hardening, the hardness of the as-sintered composites (i.e. maximum hardness of ~ 920 HV10) was increased compared to the mechanically milled UFG H13 (i.e. ~ 755 HV10), while in comparison to the as-atomized H13 (i.e. ~ 640 HV10) the improved hardness was ascribed to the synergic effect of dispersion hardening, microstructural refinement and strain hardening induced by MA. In these composites, tempering resistance at 550°C and 650°C was significantly improved due to the dispersion hardening effect. The hot compressive yield strength of the composites at 650°C and 450°C was increased up to 1.8 times the unreinforced UFG H13. t to m transformation during hot compression was evidenced and contributed to the strengthening. The hardness of the composites in heat treated condition (i.e. ~ 600 HV10) was significantly improved compared to that of the unreinforced matrix (i.e. ~ 420 HV10) while the apparent fracture toughness was drastically decreased to half the Kapp of the base material (19 MPa*m1/2 vs. 36 MPa*m1/2). However, the fracture toughness was slightly higher than that of a TiC reinforced H13 (i.e. 17 MPa*m1/2) with the same hardness (i.e. ~ 600 HV10).

Le attività di ricerca svolte nel corso del dottorato di ricerca, sono state focalizzate principalmente sullo studio dell’evoluzione microstrutturale, delle proprietà meccaniche e tribologiche di una particolare lega da fonderia, EV31A, con alte percentuali di terre rare (Nd e Gd > 4% in peso). Le analisi microstrutturali sono state eseguite tramite microscopia ottica (OM), elettronica in scansione (SEM) ed elettronica in trasmissione (TEM), mentre le proprietà meccaniche sono state determinate attraverso prove di trazione e prove di fatica a flessione rotante. Al fine di incrementare le proprietà tribologiche delle leghe di magnesio è stata valutata l’efficacia del trattamento PEO sia sulla lega EV31A, sia sulle più comuni leghe AZ80 e AZ91D, effettuando test tribologici in modalità pattino su cilindro (Block on Ring). Infine è stato condotto uno studio sull’efficacia del trattamento di fusione superficiale laser (LSM), analizzandone gli effetti sia sull’evoluzione microstrutturale, sia sulle proprietà meccaniche e sulla resistenza a corrosione. Le attività svolte nel corso del dottorato di ricerca sono state svolte presso il Dipartimento di Ingegneria Industriale DIN della Scuola di Ingegneria e Architettura dell’Università di Bologna sotto la supervisione della Prof. ssa Lorella Ceschini., The research activities carried out during the PhD course have been focused mainly on the study of microstrucural evolution, mechanical and tribological properties of EV31A Mg casting alloy, characterized by a high content of rare earth elements (Nd and Gd > wt.4%). Microstructural analyses have been carried out by optical microscopy (OM), scanning electron microscopy (SEM) and electron transmission microscopy (TEM); mechanical properties have been evaluated by tensile and rotating bending fatigue tests. Aiming to increase tribological properties of magnesium alloys the effectiveness of PEO treatment on EV31A alloy, as well as on AZ80 e AZ91D, has been studied by means of block on ring tribological tests. Moreover, the effectiveness of laser surface melting treatment has been evaluated, by studying its effects on microstructure, mechanical properties and corrosion resistance of Elektron 21 alloy. The activities have been carried out at Industrial Engineering Department of Bologna University, under the supervision of Prof. Lorella Ceschini.

Copper is widely used in many applications demanding high thermal and electrical conductivity, unfortunately its low hardness and wear resistance limit its performance. Work hardening has been proposed as a successful strengthening mechanism for the production of harder copper material, keeping the intrinsic conductivities. In this PhD thesis initially mechanical milling (MM) has been considered as suited strengthening technique due to the severe strain hardening and microstructural refinement induced by severe plastic deformation during the process. Then an enhanced hardening has been obtained by dispersion of a second harder phase in the copper matrix by mechanical alloying (MA), leading to the production of metal matrix composites (MMC). In this PhD thesis strain hardened and dispersion hardened copper materials have been sintered by Spark Plasma Sintering (SPS). Firstly the MM behaviour of Cu as function of milling time has been studied, it consists in three stages: flaking, welding and fracturing process. Since stearic acid has been added as process control agent (PCA), its decomposition has been analysed to limit the residual porosity in sintered samples. Several focused attempts have been made and the best results have been obtained by using a fine particle size, decreasing the heating rate and applying the SPS pressure once the decomposition of PCA was completed. However the presence of copper oxide and microstructure defects induced by the severe strain hardening hinder the densification. The residual porosity is responsible of a decrease of hardness in sintered sample and consequently to a limited wear resistance, to a decrease of thermal conductivity and to a loss of ductility. For the production of MMC a ceramic reinforcement (0.5wt% of TiB2) has been selected. Increasing milling time the dispersion of the hard phase among the matrix becomes more homogeneous and refinement of TiB2 is highlighted. The evolution of particle size and morphology during MA is similar to MM; also the densification mechanism during SPS are the same consisting in powder rearrangement, local and bulk deformation. The final density generally decreases by increasing milling time, by the way an increasing hardness confirms that strain hardening and dispersion hardening abundantly compensate the negative effect of porosity. Has been proved that the hard particles successfully enhanced sliding and abrasion wear meanwhile the copper matrix guarantees high thermal conductivity, satisfying the requirements. Therefore considering the characteristics of the initial copper powder, promising results have been obtained for MMCs showing an increased hardness combined with a high wear resistance and a thermal conductivity comparable to atomized copper and much higher than the commercial Cu-Be alloy. On the other side mechanical milled samples exhibited some limits, but they allowed a deep understanding of the MM process of copper.

The anisotropic dimensional change on sintering of a prior cold compacted iron was investigated by dilatometry. Shrinkage is larger along the compaction direction than in the compaction plane. This phenomenon is very pronounced during the heating ramp in alpha phase and in particular below the Curie temperature, while in austenitic field is quite poor. The results of dilatometry tests were elaborated according to the shrinkage kinetics model of classical sintering theory, to calculate an effective diffusion coefficient along the two directions, which resulted higher for direction parallel to the compaction direction than perpendicular to it. In both directions, the effective diffusion coefficient is larger than that reported in the literature for pure iron, corresponding to an equilibrium density of structural defects. It also varies during the isothermal holding time. This discrepancy is attributed to the defectiveness introduced by cold compaction, that increases diffusivity through the activation of dislocation pipe mechanism, which is particularly intense below the Curie. This interpretation may also justify anisotropy of shrinkage due to the inhomogeneous deformation of interparticle contact regions that was measured with ISE method and EBSD analysis. The anisotropic shrinkage was also described through a modified micromechanical model proposed by the continuum mechanics approach, where the porous body is composed by aligned, elongated particles and elliptic pores, whose geometrical parameters were obtained through image analysis of SEM microhgraphs. The dislocation density calculated for different sintering temperatures was comparable to that measured experimentally. The effect of green density on anisotropy of shrinkage was investigated, too. Anisotropy tends to increase with green density, because of the larger plastic deformation introduced in the interparticle regions by the compaction pressure.

The dimensional control is a crucial aspect for any manufacturing process. In Powder Metallurgy, and in particular in net shape press and sinter process, dimensional control assumes a particular relevance, since sintering of green parts involves dimensional variations that can be from 0 to 2-3% in volume. The dimensional variation in sintering is either shrinkage or swelling. Both depend on the material and on several process parameters relevant to the compaction and the sintering operations. Experimental evidences proved dimensional variations to be affected by an anisotropic behavior. This important phenomenon affects the effectiveness of the dimensional control if not opportunely taken into consideration in the design process. Professor Ilaria Cristofolini and Professor Alberto Molinari have started a deep investigation on this phenomenon, about five years ago, involving an important experimental campaign. The main idea is to collect a large quantity of data, both on ad-hoc designed samples and on parts produced by qualified PM companies cooperating with the University of Trento. The purpose is to develop a realistic model, able to explain and describe the mechanisms involved in the anisotropy of dimensional changes, and the dependence on the geometry of the parts, building a robust knowledge to improve the design methodologies in the industrial production. The present work investigates the effect of the geometrical characteristics of the part on the dimensional variations in sintering, giving a particular importance on its anisotropic behavior. The influence of geometry has been investigated using rings and disks with varying heights, external diameters and internal diameters. The influence of the sintering temperature has been also evaluated. The dimensional variation has been measured by a tri-dimensional Coordinate Measuring Machine. The anisotropy has been defined through a specifically determined parameter, which has been used to develop a predictive model estimating the anisotropy of the dimensional variations. This model has been then validated on complex parts produced by a Powder Metallurgy company.

The application of powder metallurgy (PM) technologies to the manufacturing of Oil & Gas turbomachineries’ components was investigated in the course of research collaboration with the Material and Processes Engineering Department of General Electric Oil & Gas (Italy). The thesis focused on the study of the pressure-assisted Hot Isostatic Pressing technology for the processing of the corrosion resistant Ni-base alloy N07626. The densification behaviour of the N07626 metal powder in condition of pressure assisted sintering was investigated by experiments conducted on a small scale by uniaxial hot pressing condition using a Spark Plasma Sintering (SPS) machine in the aim of extending the result to the initial stage of densification of HIP. The SPS exepriments demonstrated that the densification rate is strongly affected by the process temperature and it is less sensitive to the variation of applied pressure. The microstructure and mechanical properties of full-dense HIPped N07626 alloy, produced according to a fixed proprietary cycle and several experimental deviations were analyzed. The microstructure was studied by Optical Metallography, Scanning Electron Microscopy, Energy Dispersed X-Ray Spectroscopy and Electron Backscatter Diffraction. The mechanical properties of the alloy were assessed by tensile testing, conventional and instrumented Charpy V-Notch testing, JIC fracture toughness tests and fatigue crack growth rate testing. The tensile and impact toughness properties resulted sensitive to the local accumulation of oxygen in Oxygen Affected Zones (OAZs), that leads to a ductile to brittle transition in the impact toughness of the material. Two models for formation of OAZs were proposed based on the phase transformation and the oxidation/reduction reactions taking place in the HIP. The mechanical properties were discussed on the base of the microstructure of the Prior Particle Boundaries (PPBs) interface, focusing of the phase transformation products, represented by a thin layer of submicrometric oxides and carbides. The fracture mode was explained by the analogy with models of ductile micro-mechanisms of void nucleation and coalescence and with fracture models of particulate reinforced metal-matrix-composite. The Charpy impact toughness and the fracture toughness were correlated to the oxygen concentration and to the density of inclusions. The fatigue crack propagation behavior was discussed focusing on the effect of clustering of inclusions on the crack propagation path. A relation between the Paris slope with the impact toughness was found. Finally the increase of processing temperature (HIP and heat treatment) was found significanty beneficial for the toughness. This effect was investigate by grain-size analysis and was proposed to be related to a reduction of density of PPBs inclusions.

High pressure die casting (HPDC) is a widely used process for manufacturing components with high production rate and complex geometries. However, high pressure die casting is still considered a “defect generating process”, since an amount of 5-10% of scrap is usually detected in castings. For this reason, the availability of new standards and tools for optimizing the process is one of the prominent needs of foundry field. Both these issues are tackled in this Thesis. First, a new classification of defects and reference dies for estimating the static mechanical properties of aluminium alloys have been developed and then published as CEN Technical Reports, satisfying the need for new standards. Then, a novel and comprehensive methodology has been developed for optimizing HPDC process through the definition of meaningful behavioural models. Some newly defined process parameters have been hence introduced, by representing the most important physical phenomena affecting casting quality and the integral nature of HPDC, and an original approach is outlined. In particular, in order to provide an effective representation of the different process stages, the following parameters have been found to be more influential and effective in representing transmitted forces, mechanical energy exchange and heat removal: the root mean square acceleration in the second stage, the energy associated to the flow forces in the whole cycle, the work of the pressure forces in the third stage and the normalized thermal gradient. The first two parameters embody the plunger motion time-history, the third parameter represents the hydraulic pressure time-history, while the last one concentrates on some thermal aspects. These parameters take advantage from signal processing techniques of the measured position and pressure profiles. Four experimental campaigns (in the whole 210 castings) using different injection machines, different alloys and different geometries of the die have been carried out to validate the novel process parameters and to prove the general validity of the approach. The statistical correlation with the measured static mechanical properties, density and percentage of porosity, as well as the metallographic analysis (percentage of oxides on fracture surfaces, analysis of different kinds of internal defect) prove the soundness of the developed method. Given the significance of the plunger motion profile in explaining the casting quality, analytical models for computing the root mean square acceleration and the energy associated to the flow forces have been developed. These analytical models permit selecting in advance the best plunger motion profile, which guarantees reliability and soundness of castings, thus satisfying the need expressed by foundries for effective optimization tools.

This thesis summarizes the work carried out during the three-year Ph.D in Industrial Engineering and involve the study and characterization of coatings obtained on light alloys with the technique known as Plasma Electrolytic Oxidation (PEO). PEO process is, from the practice point of view, similar to the traditional anodic oxidation process as it's based on the electrochemical growth of a protective oxide layer on a metal surface. Compared with the traditional anodizing, PEO process works at higher currents and higher voltages, thus modifying the characteristics of the obtained layer. In recent years the importance of PEO process is increasing both in the research and in the industrial world. In fact the potentiality of the coatings obtained with this type of process are higher than those of the coatings obtained with the traditional techniques of chemical conversion or anodizing. However, the relatively high cost and some problems related to the process (in particular the need of a post treatment to ensure galvanic corrosion) have now slowed to the widespread use on an industrial scale. So the scientific research on one hand is looking for new solutions to further improve the properties of the coatings, in order to justify the higher costs, on the other is trying to modify the existing process to reduce the above-mentioned costs. The obtained results explained in this thesis have allowed an expansion in the knowledge regarding the PEO coatings and in particular to move towards greater industrial development of the technique. In fact new process parameters that permit to reduce the total time for the obtainment of good PEO coatings maintaining good corrosion resistance were found, especially working with higher current densities if compared with the ones reported in literature. Moreover the addiction of molybdenum and lanthanum salts as additives in the electrolyte used in the PEO process, has permitted to improve the performances of the coating in terms of corrosion resistance. The addiction of graphite nanoparticles and silver particles has permitted to obtain respectively coatings with improved corrosion and wear resistance and coatings with an intrinsic antimicrobial effect. PEO process was also successfully applied on steels.

The present PhD thesis summarizes the results of experimental activities carried out on the production and characterization of cast aluminum alloys and Al-based nanocomposites for room and high temperature applications. Two quaternary Al-Si-Cu-Mg alloys (A354 and C355) were studied, aiming to investigate the effect of chemical composition, solidification rate and heat treatment condition on the tensile and fatigue behavior at room and high temperature. Heat treatment optimization of A354 alloy was carried out. The overaging behavior of A354 and C355 alloys was compared to that of A356 (Al-Si-Mg) alloy, in order to evaluate the thermal stability of the alloys. As a result, the concurrent presence of Cu and Mg confers, by precipitation hardening, enhanced mechanical properties and higher thermal stability in comparison to the traditional Al-Si-Mg alloy. A preliminary study aimed to evaluate the effect of Molybdenum addition on A354 overaging response was also carried out. Enhanced mechanical properties after long-term overaging were registered in A354-0.3wt.%Mo alloy, in comparison to the base A354. Casting techniques for the production of Al-matrix composites were implemented at the laboratory scale. The stir-casting method assisted with ultrasonic treatment and in situ reactive casting were applied to produce Al2O3-A356 micro/nanocomposites and ZrB2-A356 composites, respectively. Friction Stir Process (FSP) was evaluated as possible solid state processing route to: (i) enhance Al2O3 nanoparticles distribution in a semisolid processed AA2024-based nanocomposite, and (ii) directly distribute Al2O3 nanoparticles into AA7075 alloy at the solid state. Experimental results highlighted difficulties in obtaining an even distribution of nanoparticles, by both liquid and semi-soli state routes, due to the low wettability of nano-sized ceramic reinforcement. The application of FSP led to enhanced nanoparticles distribution, mitigation of casting defects associated to nanoparticles addition (porosity, nanoparticles clusters) and microstructural homogenization, thus allowing to better exploit nanoparticles strengthening effect.

The implantation of stents is an effective procedure to unblock the arteries of patients with serious heart problems. Traditionally, stents are made of inert materials such as stainless steel and titanium alloys. It has been shown that the traditional stents can cause restenosis or thrombosis. In recent years the proposal of biodegradable stents is attracting the interest of the industry and the research, since the stent is mechanically needed only in the first year, eliminating the problems caused by the long duration of the implant. Magnesium (Mg) alloys are of increasing interest because of their engineering properties, including the high strength to density ratio. Recently, they have been also proposed as biomaterials for the production of bioabsorbable stents and for other medical devices due to its harmless effect to human body when compared with other structural materials. In this work, the possibility to produce biodegradable stents made of magnesium starting from the powder is investigated. Pure Mg and the AZ91 Mg powders were used in the present study. Pure Mg powder was sintered by Spark Plasma Sintering at 400 and 470 °C, and the AZ91 powder was sintered at 400 °C without homogenization and at 470 °C after homogenization. The preforms produced by sintering were then submitted to hot compression, rod extrusion and tube extrusion at 330 and 380 °C with different strain rates. During all the process was not possible to obtain recrystallization or grain refinement on pure Mg, and after the tube extrusion it has shown a high brittleness and sever defects, which led to the decision of proceed only with AZ91 alloy. The AZ91 presented good recrystallization in al process, always following the Zener-Hollomon relation. The grain size obtained was as small as 1.5 μm. The AZ91 tube was then submitted to manual machining and laser cutting and it was possible to obtain the stent precursors. The results of the present investigation have demonstrated the suitability of the proposed route for producing Mg-based stents. It is clear, however, that the process has to be further optimized, investigating also the possibility of using different types of powder with a tailored composition.

the influence of the powder material and the main processing parameters on geometrical features and dilution of the clads is investigated and discussed. Physical and analytical model that allow the explanation of the process and the prediction of the clad geometry and dilution is discussed. Using these models, useful tools for cladding operators and engineers are proposed. The energetic balance of the process is presented. Energetic redistribution in laser cladding process is analysed in detail, and quantification of process efficiency and energy losses is given. The influence of the processing parameters and the chemical/physical properties of the materials is considered throughout the various experiments performed. Some selected properties of the coating produced in different processing conditions are analysed. In specific, the variation of the chemical composition of the clad due to substrate dilution is considered, and its effect on the characteristics of the coatings is discussed.

A metal injected component was produced by overmolding technique. To reach a good result differebnt powder matching were studied. The final mechanical properties and corrosion resistance of the interface microstructure were investigated.

Currently the whole Italian industry suffers the competition from emerging markets. All the social partners realized that our low-tech products and know-how are unlikely to be competitive in comparison with those produced at lower cost in other emerging countries. Historically, the Italian metalworking and mechanical engineering industry, and in particular the construction sector as complex welded pressure vessels, large structures for civil and shipbuilding, is considered among the best and the most famous in the world, this is because our products are recognized as being of excellent overall quality, with a touch of design and typical Italian good taste, which is difficult to reproduce or to copy. We still have many customers who come to the metalworking and mechanical engineering companies to buy Italian welded because in this way they have reasonable assurance that your product has the quality standards required by international standards and their internal specifications. At this point, it becomes essential that the national metalworking and mechanical engineering industry points to increase its know-how and to develop new technologies and products which are higher than those already on the market. In this context it should be framed this "Doctoral thesis" that documents a part of the enormous economic effort and resources in research and development expenses that a typical Italian company has made in order to demonstrate to its customers to have technological knowledge and production capacity at the spearhead which can guarantee them a finished product with quality, better technology and more advanced than those that could be found somewhere else. The company to which you refer is the De Pretto Industrie in Schio, near Vicenza, in what once was called by many the heart of the Italian metalworking and mechanical engineering industry, and their group company forging master FOC Ciscato. With this background, the idea of Doctoral Thesis proposed which describes the research and development of metallurgical problems and weldability for products of De Pretto Industrie and FOC Ciscato. Realized during the three years of the PhD and developed, in collaboration with the University of Padova, within the normal industrial production of the Companies to which I belong; and that for their innovative aspects were considered worthy of publication. In particular the following specific topics have been analyzed and studied: • Development of a welding procedure blade-crown and shaft-rotor forged by rotor of a steam turbine • Manufacturing problems on the close die and open die forging pieces in super duplex stainless steel • Characterization of welded joints in super duplex stainless steel for Offshore applications • Comparative analysis of the methods for the determination of the percentage of ferrite for steel welded joints duplex stainless steel