Zn redukcija iš šarminių elektrolitų vyksta per tarpinę oksido/hidroksido fazės susidarymo stadiją. Dalis oksidinių junginių gali būti neredukuojami, todėl terptis į metalinę dangą. Impulsinės elektrolizės taikymas Zn dangų nusodinimui yra vienas iš būdų modifikuoti metalo struktūrą ir tuo pačiu pagerinti dangų korozinį atsparumą. Nemetalinių intarpų kiekis impulsine elektrolize nusodintose Zn ir jo lydinių dangose nėra tyrinėtas. Nemetalinių intarpų kiekis buvo nustatytas dangų anodinio tirpinimo Na2SO4 + Na2 EDTA tirpale ir Rentgeno fotoelektronų spektroskopijos metodais. Nustatyta, kad oksidinių intarpų kiekis impulsine elektrolize nusodintose Zn ir Zn-Ni dangose buvo didesnis, lyginant su nuolatinės srovės dangomis, taip pat į Zn dangas, lyginant su lydinių, įsiterpia daugiau oksidinių junginių. Nuolatine srove nusodintose Zn dangose ZnO kiekis yra didesnis už Zn(OH)2, tačiau impulsinė elektrolizės taikymas didina hidroksido kiekį dangoje. Nuolatine srove nusodintose Zn-Ni dangose oksido ir hidroksido intarpų kiekiai yra panašūs, tuo tarpu impulsinė elektrolizė ženkliai padidina hidroksido kiekį dangoje. / Electrodeposition process of Zn in alkaline solutions occurs through oxide/hydroxide phase formation, which under certain conditions could not be totally reduced and therefore formation of non metallic (oxide/hydroxide) inclusions can take place. Pulse plating of metal coatings is widely used as the method for metal structure modification in order to enhance the corrosion resistance of Zn and Zn alloy coatings, however the amount of inclusions in pulse plated Zn and Zn-Ni coatings was not investigated up to date. The amount of non-metallic inclusions was determined from anodic dissolution curves, obtained in Na2SO4 + Na2 EDTA solution and from X-ray photoelectron analysis of the sample surfaces after Ar ion sputtering. The amount of the oxide phase in Zn and Zn-Ni coatings was determined to be higher in the pulse plated coatings with respect to direct current ones, while in Zn coatings this amount was also higher with respect to the alloy. The amount of ZnO in the inclusions of direct current plated Zn coatings is higher than that of Zn(OH)2, however, application of pulse deposition increases the amount of the latter compound. Oxide and hydroxide amounts in the direct current plated Zn-Ni coatings are similar, meanwhile, the pulse plating increases significantly the amount of hydroxide phase.

This thesis research investigates the surface properties and performances of gold nanoparticles, microarc oxidation coating, and epitaxial nano-twinned copper film. The research aims to understand the critical behavior of material surfaces in order to facilitate design and development of new materials for tribological applications. The research will focus on improving of the gun barrel performances. Experimental approaches will be used for combining analysis with basic thermal energy transfer principles. Results obtained here will be used for developing new materials to be used in facilitating gun barrels. Experimental approach includes scanning calorimetry-thremogravimetric analysis, tribological testing, and potentiodynamic polarization. The fundamental understanding obtained here will be beneficial for the gun barrel design, manufacturing, and military technologies followed by the results of experiments with different three types of materials. The results of this research showed that the coatings with microarc oxidation and nano-twinned structure improved wear resistance from the tribological examinations and size of AuNPs affected their thermal behaviors measured by differential scanning calorimetry and thermogravimetric analysis method.

No description available.

No description available.

The rise of the Environmentalism in every sector of the Industry has lead the aircraft and engine manufacturing companies to develop new generations of more environmentally friendly engines. The companies, encouraged to this purpose, are in a constant research for new manufacturing and production techniques, in order to improve their products, from the environmental point of view, by gaining efficiency in the manufacturing techniques and reduce the fuel consumption and emissions in-flight. Having in mind this scenario, the sponsor of this Project is interested in understanding how changing the materials of the blades, titanium alloys currently, for other lighter materials, such as composites, is going to have an effect in the overall gas turbine efficiency. In the particular case of this Project, it will be studied the influence of the Stiffness and coating Thickness of those non-metallic materials suitable to be employed as coatings on gas turbine fan blades, from the icing point of view. The work procedure will be based on a study of Linear Elastic Fracture Mechanics of bi-material junctions and will extrapolate the general problem to the ice-coatings case, by getting experimental data from tests carried out in an Icing Tunnel. It will be observed that the coating Stiffness has an influence on the Adhesion Level of ice to less stiff materials, if compared with the Adhesion Level of ice to metals. Besides, it will be described how a 0.5 millimetres thin polymeric coating placed over a metallic substrate is enough to reduce the Adhesion Level of ice, hiding any effect that the underneath materials might have on the Adhesion Level.

No description available.

The rise of the Environmentalism in every sector of the Industry has lead the aircraft and engine manufacturing companies to develop new generations of more environmentally friendly engines. The companies, encouraged to this purpose, are in a constant research for new manufacturing and production techniques, in order to improve their products, from the environmental point of view, by gaining efficiency in the manufacturing techniques and reduce the fuel consumption and emissions in-flight. Having in mind this scenario, the sponsor of this Project is interested in understanding how changing the materials of the blades, titanium alloys currently, for other lighter materials, such as composites, is going to have an effect in the overall gas turbine efficiency. In the particular case of this Project, it will be studied the influence of the Stiffness and coating Thickness of those non-metallic materials suitable to be employed as coatings on gas turbine fan blades, from the icing point of view. The work procedure will be based on a study of Linear Elastic Fracture Mechanics of bi-material junctions and will extrapolate the general problem to the ice-coatings case, by getting experimental data from tests carried out in an Icing Tunnel. It will be observed that the coating Stiffness has an influence on the Adhesion Level of ice to less stiff materials, if compared with the Adhesion Level of ice to metals. Besides, it will be described how a 0.5 millimetres thin polymeric coating placed over a metallic substrate is enough to reduce the Adhesion Level of ice, hiding any effect that the underneath materials might have on the Adhesion Level.

In this thesis, research on synthesis, structure and characterization of amorphous carbide-based thin films is presented. Crystalline and nanocomposite carbide films can exhibit properties such as high electrical conductivity, high hardness and low friction and wear. These properties are in many cases structure-related, and thus, within this thesis a special focus is put on how the amorphous structure influences the material properties. Thin films within the Zr-Si-C and Cr-C-based systems have been synthesized by magnetron sputtering from elemental targets. For the Zr-Si-C system, completely amorphous films were obtained for silicon contents of 20 at.% or higher. Modeling of these films, as well as experimental results suggest that the films exhibit a network-type structure where the bond types influence the material properties. Higher hardness and resistivity were observed with high amounts of covalent Si-C bonds. Several studies were performed in the Cr-C-based systems. Cr-C films deposited in a wide composition range and with substrate temperatures of up to 500 °C were found to be amorphous nanocomposites, consisting of amorphous chromium carbide (a-CrCx) and amorphous carbon (a-C) phases. The carbon content in the carbidic phase was determined to about 30-35 at.% for most films. The properties of the Cr-C films were very dependent of the amount of a-C phase, and both hardness and electrical resistivity decreased with increasing a-C contents. However, electrochemical analysis showed that Cr-C films deposited at higher substrate temperature and with high carbon content exhibited very high oxidation resistance. In addition, nanocomposite films containing Ag nanoparticles within an amorphous Cr-C matrix were studied in an attempt to improve the tribological properties. No such improvements were observed but the films exhibited a better contact resistance than the corresponding binary Cr-C films. Furthermore, electrochemical analyses showed that Ag nanoparticles on the surface affected the formation of a stable passive film, which would make the Cr-C/Ag films less resilient to oxidation than the pure Cr-C films.

No description available.

Fretting and wear are recurrent problems in the field of aeronautics. Contacts the blade / disk at the compressor or high-pressure turbine aircraft engines, for example, are subjected to high stresses at high temperatures. The challenge for manufacturers is to maximize the lifetime of these components and be able to predict crack initiation. To improve handling parts, coatings are used to protect them. Materials and their mechanical properties have a direct impact on the contact and the lifetime. The choice of materials, number of layers, the thickness of the order are therefore essential. By their composition (fibers, single crystals), elaboration (extrusion) or their mode of deposition, the hypothesis to consider homogeneous isotropic materials is too simplistic. Anisotropy is an important parameter to take into account in the design. Composite materials are increasingly used in the aeronautic. In this context, this thesis aims to study the behavior of anisotropic homogeneous materials, focusing on the influence of the main parameters mechanical characteristics of a material to better understand their effects. We focus on the Young's modulus (or modulus of elasticity), the module Coulomb (or shear modulus) and the Poisson's ratio, and values ​​in different directions. As expected, the Young's modulus in the direction normal to the contact plays an important role in determining the pressure profile. However, the influence of Young modulus in the plane tangent to the contact is not to neglect it also alters the shape of the contact area. The orientation of the material with respect to the contact is therefore a parameter to take into consideration, it can directly reduce or enhance the effect of Young's modulus in a direction privileged. The module Coulomb and Poisson's ratio were also analyzed. As a result they significantly affect the contact. These results are confirmed in the case of a coated solid, unlike the effects of coating and substrate can compensate. The impact properties of the coating will be even more important than it is thick. The scale of the contact relative to the materials used is also important on the pressure profiles. A comparison between the model anisotropic homogeneous and isotropic heterogeneous model have been performed. At mesoscopic scale, the composite is composed of a matrix with fibers that induce pressure peaks while at the macroscopic level, the composite material is seen as a homogeneous material, the pressure profiles are smoothed.