In the areas of aeronautics and aerospace, ceramic composites play an essential and increasing role due to their superior performance and tailorable properties, exhibiting highly specialized mechanical, thermal, and electric features1. Their main applications include thermal protection systems (TPS), thermal barrier coatings (TBC), and dielectric barrier discharge (DBD) plasma actuators, both for instrumentation and control purposes2. This work reports the manufacture and characterization of three ceramic composites capable of fulfilling the multifunctional ceramic condition according to the aforementioned applications. Accordingly, MgO-Al2O3 (MA), MgOCaZrO3 (MCZ), and Y2O3 stabilized ZrO2 (YSZ) are introduced for TPS, TBC, and DBD dielectric elements. To this aim, MA, MCZ, and YSZ ceramic composites were fabricated via a sequential process, encompassing the selection of raw powders and milling, die pressing, and sintering. Further, the samples were polished for surface optimization. Overall, the results obtained, including mechanical (Young’s and shear moduli, flexural strength, hardness, and fracture toughness), thermal (thermal conductivity and thermal expansion (CTE)), and electrical (dielectric constant) properties, report evidence that the developed ceramics show suitable multifunctional characteristics and therefore fulfil the aeronautical and aerospace demands for increased materials performances. The combined analysis of the Young’s and shear moduli (Fig.1a) with the CTE – the latter over a wide range of temperatures (Fig. 1b) – allows concluding that the cost-effective and widely used alumina appears suitable for bulk monolithic (TPS) and joint applications (TPS, TBC, and DBD).

The quest for increased performance in the aeronautical and aerospace industries has provided the driving force and motivation for the research, investigation, and development of advanced ceramics. Special emphasis is therefore attributed to the ability of fine ceramics to fulfill an attractive, extreme, and distinguishing combination of application requirements. This is impelled by ensuring a suitable arrangement of thermomechanical, thermoelectric, and electromechanical properties. As a result, the reliability, durability, and useful lifetime extension of a critical structure or system are expected. In this context, engineered ceramic appliances consist of three main purposes in aeronautical and aerospace fields: thermal protection systems (TPS), thermal protection barriers (TBC), and dielectric barrier discharge (DBD) plasma actuators. Consequently, this research provides an extensive discussion and review of the referred applications, i.e., TPS, TBC, and DBD, and discusses the concept of multifunctional advanced ceramics for future engineering needs and perspectives.

ABSTRACT In the current study, the influences of laser remelting treatment on NiCoCrAlY/ZrO2-7 wt.% Y2O3 thermal barrier coatings fabricated via plasma spraying on GH4169 alloy were examined. The microstructure, microhardness, hot corrosion resistance at 950 ℃ of the two types of TBCs were investigated comparatively. The results indicated that the as-sprayed TBCs had a lamellar structure with high cracks and porosity. After laser remelting treatment, a laser remelted layer with a compact sub-micro sized grains arranged in a stacked structure was formed which was denser than that of the as-sprayed TBCs. The surface microhardness of the as-sprayed TBC was only 977 HV0.3, which exhibited a significant increase (over 1500 HV0.3) after laser remelting due to the fine grains of the remelted region with lower porosity. The hot corrosion resistance of the laser remelted TBCs were considerably better than the as-sprayed one. The as-sprayed TBC with a lot of defects, the molten salts could easy penetrate the coating and react with Y2O3. The consumption of Y element promoted the phase transition of t'-ZrO2 to m-ZrO2, which harmed the protective coating because of the volume expansion of the phase transition. The laser remelted TBCs was dense, which could significantly reduce the penetrate of molten salts due to the fewer cracks and holes compared to the as-sprayed TBCs. The laser remelted TBCs exhibited superior hot corrosion performance as compared to the as-sprayed TBCs.

In this work we started by doing a introduction to the ceramic thermal barrier coatings, especially in the utilization of this kind of material as top coat by presenting its fundamental properties. After we present new materials that may replace zirconia partially stabilized with yttria (PSZ), being this last material the most used as top coat. In this work, we also make a brief description of the processing methods for each material analyzed in this article. Last we present a table when some of the most important thermalphysical properties of the materials studied.

Thermal Barrier Coating (TBC) systems are frequently used in gas turbine engines to provide thermal insulation to the hot-section metallic components and also to protect them from oxidation, hot corrosion and erosion. Surface sealing treatments, namely laser-glazing, have been showing a high potential for extending in-service lifetimes of these systems by improving chemical and thermo-mechanical resistance. In this investigation, both as-sprayed and laser-glazed TBCs were exposed to hot corrosion in molten salts. The glazed coatings were obtained by scanning the surface of the plasma-sprayed coatings with either a CO2 or a Nd:YAG laser. The hot corrosion investigation was accomplished by subjecting the specimens to an isothermal air furnace testing under V2O5 and/or Na2SO4 at a temperature of 1000 °C for 100 h. Spallation has been observed in coatings in the as-sprayed condition under V2O5 or V2O5+Na2SO4. Na2SO4 itself had no or minimal effect on the degradation of the laser-glazed or as-sprayed condition coatings, respectively. The degradation in V2O5 was accomplished by destabilization of YSZ as a consequence of depletion of yttria from the solid solution to form YVO4 and therefore led to the disruptive transformation of the metastable tetragonal phase to the monoclinic phase. Moreover, the presence of both corrosive salts induced the formation of large high aspect ratio YVO4 crystals that introduced additional stresses and contributed to the degradation of the coatings. The laser-glazed specimens were not efficient in avoiding the molten salt penetration along the thickness direction due to the presence of cracks on the glazed layer. However due to a reduced specific surface area of the dense glazed layer, the corrosion reaction of the molten salts with the YSZ has been lower than in coatings in the assprayed condition.

Laser glazing has been revealing a high potential for the improvement of plasma-sprayed (PS) thermal barrier coatings (TBCs) by reducing surface roughness, eliminating open porosity on the surface and generating a controlled segmented crack network, although the relationship of the processing parameters with the resultant properties has not yet been completely established. In this investigation, TBCs consisting of atmospheric plasma-sprayed (APS) ZrO2–8wt.%Y2O3 were subjected to a CO2 continuous wave laser-glazing process in order to seal its surface porosity, generating an external dense layer. For that purpose, different amounts of radiation resulting from different scanning speeds were applied to the specimens as well as different track overlapping. Results have shown a significant decrease of the surface roughness after the laser treatment. All specimens presented a fully dense and porous free external layer with a polyfaceted columnar microstructure highly adherent to the plasma-sprayed coating. Controlled surface crack networks, extremely dependent on the laser scanning speed and track overlapping, were achieved for each set of processing parameters. The cracks were found to have a tendency to be oriented in two perpendicular directions, one in the direction of the laser-beam travel direction, the other perpendicular to it. Moreover, the cracks parallel to the beam travel direction are found to be on the overlapping zone, coinciding with the edge of the subsequent track. The cracks are perpendicular to the surface along the densified layer and tend to branch and deviate from the vertical direction below it, within the porous PS coating. XRD results revealed mainly tV nontransformable tetragonal zirconia with a small percentage of residual monoclinic zirconia for the as-sprayed coating. All glazed coatings presented only tV nontransformable tetragonal zirconia with some variations on preferable crystal orientation. Grain sizes varied from 26 to 52 nm, increasing with an increase of laserirradiated energy; microstrain behaved inversely.

A energia é possivelmente um dos maiores desafios que a União Europeia terá de enfrentar nas próximas décadas, sendo necessário implementar estratégias para a utilização mais eficiente dos recursos energéticos nos edifícios, como por exemplo através da climatização inteligente dos edifícios (arrefecimento e aquecimento passivos) ou da conversão da energia solar em eletricidade. Neste trabalho é descrito o desenvolvimento de revestimentos poliméricos funcionalizados com óxidos metálicos e iões de terras raras, que potenciam a conversão da energia solar em eletricidade e a climatização eficiente dos edifícios através da sua integração em janelas inteligentes. Estes sistemas de concentração e conversão de energia solar, baseados em materiais luminescentes, são designados por LSC’s (Concentradores Solares Luminescentes). O estudo centrou-se na síntese de nanopartículas ocas de sílica pelo método de sol-gel, funcionalização destas com Eu3+ ou Nd3+:Yb3+ e posterior incorporação em filmes poliméricos, otimizados para aplicação em substratos de vidro. Ao longo do trabalho efetuou-se a caracterização morfológica, química e térmica dos materiais desenvolvidos, recorrendo às técnicas de SEM-EDS, STEM, DLS, XRD, FTIR, espetroscopia de UV-Vis, UV-Vis NIR e de fluorescência e TGA. A avaliação de desempenho dos protótipos de LSC’s construídos foi efetuada com base na determinação da eficiência de conversão energética, e na monitorização das propriedades de barreira térmica do revestimento polimérico aditivado com as sílicas. Obtiveram-se revestimentos transparentes (transmitância > 90% na região do visível do espetro solar), com um excelente efeito de barreira térmica (em alguns casos capazes de produzir um abaixamento térmico até 10 °C). No geral, desenvolveram-se com sucesso materiais funcionais, para aplicações em janelas inteligentes, nomeadamente revestimentos poliméricos de elevada transmitância, em substratos de vidro, com dupla funcionalidade: barreira térmica e concentração/conversão energética.