Mechanical Behaviour of Air-plasma Sprayed Functionally Graded YSZ-Mullite Environmental Barrier Coatings: A Study via Instrumented Indentation

6 páginas, 7 figuras, 1 tabla.-- Comunicación presentada al 33th International Thermal Spray Conference & Exposition 2010; Thermal Spray: Global Solutions for Future Applications.-- et al.Mullite (Al6Si2O13) is the basis of efficient environmental barrier coatings (EBCs) for protecting Si-based ceramic matrix composites (CMCs) selected to replace specific hot-section metallic components in advanced gas turbines. Furthermore, YSZ-mullite multilayer architectures with compositional grading between the bond coat and YSZ top coat were envisioned as solutions to ease their coefficient of thermal expansion (CTE) mismatch induced stress. Consequently, a proper understanding of the mechanical properties such as the elastic modulus, hardness or plastic/elastic recovery work serve for an efficient design of such refractory oxide multilayers. In this work, three different mullite powder morphologies (fused and crushed, spray-dried and freeze-granulated) were employed. Using depth-sensing indentation with loads in the range 100 – 500 mN, the role of the microstructure and morphology of the powder feedstock on the mechanical behaviour of air plasma sprayed mullite bond coats deposited on SiC Hexoloy substrates was investigated. Fully crystalline as-sprayed mullite coatings were engineered under controlled deposition conditions. Mechanical properties were measured for the as-sprayed coatings as well as for coatings heat-treated at 1300oC, in water vapour environment, for periods up to 500 h. Both E and H values of the coatings are found to be highly dependent on the morphology of the starting powders.This work has been supported by NRC-CSIC program (project 2007CA003).Peer reviewe

Efecto de la orientación de los rodillos en la resistencia mecánica de estructuras 3D porosas de SiC fabricadas mediante impresión de filamento

[EN] The present work explores the strength enhancement via minor modifications of the pat-tern design in pure light SiC woodpile structures created by filament printing. In particular,the effect of the filament stacking angle on both the compression resistance and the elasticmodulus of these structures are evaluated. Different patterns were designed while main-taining the bulk structure density, therefore the differences in the mechanical data (strengthand elastic modulus) are not attributable to density variations. All of these materials werepartially sintered at intermediate temperature for additional porosity enhancement. More-over, SiC specimens made by full filament overlapping were produced to serve as referencemassive material. Remarkably, the massive SiC printed material displays ordered sphericalporosity and a closed-pore foam appearance, thus revealing a novel route for producingthese type of porosity. Results evidence that the structure robustness can be tuned throughslight design modification, which thus offers the possibility of further structure lighteningwithout reducing the target strength.[ES] El presente trabajo explora la mejora de la resistencia mecánica de estructuras ligeras for-madas por apilamiento de rodillos de SiC puro, procesadas por impresión directa de tinta, através de modificaciones menores del patrón de dise ̃no. En particular, se evalúa el efecto del ángulo de apilamiento de los filamentos sobre la resistencia a la compresión y el móduloelástico de estas estructuras. Los diferentes patrones fueron dise ̃nados manteniendo sim-ilares densidades aparentes de las estructuras, por lo tanto, las diferencias observadas enlos resultados mecánicos (resistencia y módulo elástico) no son atribuibles a variaciones dedensidad. Todas las estructuras se sinterizaron parcialmente para mantener una elevadaporosidad. Además, se produjeron muestras de SiC macizas creadas por la superposiciónde filamentos utilizadas como material masivo de referencia. Curiosamente, este materialmuestra una porosidad esférica y ordenada, y presenta la apariencia típica de esponjas conporosidad cerrada, mostrando en consecuencia una ruta alternativa para la fabricación deeste tipo de materiales celulares. Dado que la robustez de estructuras 3D se puede maximizara través de una ligera modificación del dise ̃no, esto permitiría alternativamente aligerar aúnmás las estructuras sin perjudicar su resistencia.This work was supported by projects MAT2015-67437-R and RTI2018-095052-B-I00 financed by the Ministerio de Ciencia, Innovación y Universidades MCIU (previously MINECO),Spain/FEDER (UE). J.J. Moyano acknowledges the financialsupport of MCIU/FEDER through the FPI contract ref: BES-2016-077759Peer reviewe

The effect of microstructure on the tribological behaviour of monolithic Si3N4 and Si3N4–SiC composites

[ES] Se ha analizado el comportamiento tribológico de materiales de Si3N4 y de compuestos Si3N4/SiC, desde temperatura ambiente hasta 700ºC y en el rango de velocidades 0.5-2 m/s. Los materiales se han preparado mediante prensado en caliente a 1750ºC en atmósfera de nitrógeno, variando el contenido en fase α- Si3N4, el tamaño medio de grano, y la morfología de las partículas de SiC adicionadas. Los ensayos se han realizado en pares homólogos utilizando un tribómetro del tipo punta sobre disco, sin lubricación y a una carga constante de 5 N. Las superficies de desgaste de las puntas y los discos se observaron en un microscopio electrónico de barrido con capacidad analítica (MEB-EDX). Los residuos generados durante los ensayos se analizaron mediante MEB-EDX y difracción de rayos X (DRX). Los resultados obtenidos en los ensayos daban valores de coeficiente de fricción, f, y de desgaste, K, superiores a 0.3 y 10-6 mm3N-1m-1, respectivamente. El mecanismo de desgaste predominante dependía de la microestructura y de las propiedades mecánicas del material ensayado.[EN] The tribological behaviour of various Si3N4 based materials, including Si3N4/SiC composites, has been analysed from room temperature up to 700ºC, and for sliding speeds between 0.5 and 2 m/s. Materials have been prepared by hot pressing at 1750ºC in nitrogen atmosphere, varying α- Si3N4 phase content, microstructure coarseness and shape and size of the SiC particles. Wear tests were performed in self-mated pairs using a pin on disc tribometer, without lubrication and at a fixed load of 5 N. Pin and disc worn surfaces were observed by scanning electron microscopy (SEM-EDS). Debris generated during tests was analysed by SEM-EDS and X-ray diffraction (XRD). Results showed friction, f, and wear coefficients, K, above 0.3 y 10-6 mm3N-1m-1, respectively. Wear mechanism depended on the microstructure and the mechanical properties of the materials.Los autores agradecen la financiación recibida del Ministerio de Educación y Ciencia (España), programa de Acciones Integradas (Proyecto No. HP97-0046), de la CYCIT (Proyecto No. MAT97-708) y del Conselho de Reitores das Universidades Portuguesas (Proyecto de Acciones Integradas E-63/98).Peer reviewe

Superior Performance of Ablative Glass Coatings Containing Graphene Nanosheets

Glass compositions in the Y₂O₃-Al₂O₃-SiO₂ (YAS) system are envisaged as promising coatings for high‐temperature protection, in particular for the thermal protection systems (TPS) looked for aerospace applications. Recently, thermally sprayed YAS hybrid coatings containing a small amount of graphene nanoplateletes (GNPs) showed enhanced performance as compared to the blank YAS coating, demonstrated by the occurrence of unusual electrical conductivity for these glasses and the development of better mechanical compliance, both phenomena associated with the presence of GNPs. Nevertheless, a crucial issue is to demonstrate if these kinds of coatings would also have superior behavior under ablation conditions, particularly regarding the mentioned TPS applications. This work goes far beyond, exploring the ablative behavior of new YAS/GNPs coatings flame sprayed over SiC substrates. These essential tests were carried out under laboratory conditions, reaching limit temperatures of 1350°C while blowing gas. Results evidence that hybrid coatings having just 1.05 vol% GNPs show enhanced ablation resistance, actually withstanding up to 30 thermal cycles (between 200°C and 1350°C) without apparent damage. This satisfactory performance is linked to the benefits of the GNP additions, and fundamentally to the higher emissivity and the directional thermal conduction characteristics of the hybrid coatings—produced by the formation of a GNP network with a preferential surface parallel arrangement—that preclude the creation of hot spots and also hinder heat propagation toward the substrate; accordingly, coating degradation is constrained to the uppermost layer of these coatings

Quemador poroso

Quemador poroso adaptado para ser alimentado con diferentes tipos de gases, que comprende un soporte que incluye un conducto a través del cual entra una mezcla de aire/gas en el quemador poroso, y una estructura cerámica, soportada por el soporte, que comprende una esponja inicialmente polimérica que se impregna con una barbotina, comprendiendo dicha barbotina al menos un material cerámico. La estructura cerámica tiene una porosidad final de entre aproximadamente 50 ppi hasta aproximadamente 70 ppi, y una densidad final de entre aproximadamente 0.45 hasta aproximadamente 0.65 g/cm3.Peer reviewedConsejo Superior de Investigaciones Científicas (España), P.I. Prosider Ibérica S.A, Ikerlan S COOPB1 Patente sin examen previ

Development of HVOF-sprayed nanostructured TiO2 coatings for high temperature applications

Peer reviewed: YesNRC publication: Ye

The Decisive Role Played by Graphene Nanoplatelets on Improving the Tribological Performance of Y2o3-al2o3-sio2 Glass Coatings

Graphene nanoplatelets (GNPs) have proved to be effective fillers for enhancing the mechanical and tribological properties of bulk ceramics and glasses, also with the added benefit of developing electrical and thermal functionalities. Similarly, enhanced transport performance has recently been shown for glass-ceramics coatings of the Y2O3-Al2O3-SiO2 (YAS) system containing a small amount of GNP fillers, intended for applications in the aerospace industry. In the present work, the wear and friction behaviour of GNP/YAS coatings –containing 0, 1.2 and 2.3 wt.% GNPs- on silicon carbide substrates is evaluated. The flame spraying process used for coating fabrication induces a structure of splats oriented parallel to the substrate with GNPs located at the inter-splat boundaries forming a connected network of platelets mainly oriented parallel to the surface as well. Unlubricated ball–on-plate reciprocating wear tests show that both the friction coefficient and the wear rate decreased by 35% and 65%, respectively, for 2.3 wt.% of GNPs. A wear mechanism for GNP/YAS coatings based on both the progressive exfoliation of the graphene sheets and the effect of the GNPs on preventing crack propagation within the coating is proposed

3D printing of cubic zirconia lattice supports for hydrogen production

The demand for hydrogen has extraordinarily grown during the last years, being one of the most attractive forms of fuels to produce green energy. Cubic zirconia ceramics are considered promising catalytic supports, and the additive manufacturing of porous 3D structures based on these ceramics could enhance their catalytic performance. Herein, lightweight highly porous (up to 88%) 3D patterned 8 mol% yttria-stabilized cubic zirconia (8YSZ) scaffolds are manufactured by robocasting from pseudoplastic aqueous-based inks to produce catalytic supports for the hydrogen (H2) production. These scaffolds are thermally treated at temperatures ranging between 1000 and 1400 ◦C and, hence, mechanically and electrically characterized. 3D 8YSZ structures sintered at 1200 ◦C, with an appropriate balance between high porosity (86%) and compressive strength (3.7 MPa), are impregnated with palladium (Pd) catalytic nanoparticles and employed in the catalytic dehydrogenation of renewable formic acid (FA) using a fixed-bed reactor. 3D Pd/8YSZ catalyst leads to the continuous production of CO-free H2 with a FA conversion of 32% at T =55 ◦CThis work was supported by the Spanish Government through RTI2018-095052-B-I00, PID2019-105079RB-I00 (MICINN/AEI/FEDER, UE), PID2021-125427OB-I00 (MICINN/AEI/FEDER, UE) and EIN2020- 112153 (MCINN/AEI/10.13039/501100011033) projects, the latter also supported by the European Union through “NextGenerationEU/ PRTR”. M. Koller gratefully acknowledges funding within “Support for International Mobility of Researchers of the Institute of Thermomechanics, Czech Academy of Sciences, part II”, no. CZ.02.2.69/0.0/ 0.0/18_053/0017555 of the Ministry of Education, Youth and Sports of the Czech Republic funded from the European Structure and Investment Funds (ESIF). G. Vega acknowledges the Universidad Aut´onoma de Madrid for the Predoctoral contract. The authors thank J. Mejía for her permanent technical assistance in the catalytic experiment

Understanding the active sites of boron nitride for CWPO: An experimental and computational approach

[EN] Hexagonal boron nitride (h-BN) has been explored as a catalyst for degrading persistent organic pollutants in wastewater by Catalytic Wet Peroxide Oxidation (CWPO). Herein, the superior activity of the h-BN on the phenol degradation (model pollutant) compared to other metal-free catalysts, such as carbon-based ones, and the lower selectivity to CO encourage the potential application of h-BN catalysts in CWPO processes. Through a combined density functional theory calculations, experimental reactions and catalyst characterization approach, a comprehensive study on the reaction mechanism has been conducted. According to this, only defected B atoms in the h-BN layer, protonated as B-(OH), decompose the hydrogen peroxide into highly reactive hydroxyl radicals. The radical species diffuse towards inner h-BN regions and react with the phenol adsorbed by π-π interaction on the h-BN surface. Oxidation by-products cause carbonaceous deposits and progressive deactivation of the h-BN catalyst that can be directly regenerated by burning off in air.The authors thank the financial support by the Community of Madrid and the Government of Spain through the projects: S2018/EMT- 4341 and RTI2018-095052-B-I00 (MCIU/AEI/FEDER, UE), respectively. The work done at the University of Sevilla was funded by Spanish Ministerio de Ciencia e Innovación and EU-FEDER, grant PID2019-106871 GB-I00, and the Junta de Andalucía-FEDER, grant: US-1381410. Also, G. Vega acknowledges the Community of Madrid for the Predoctoral contract PEJD-2018-PRE/AMB-9019, co-financed by the European Social Fund through the Youth Employment Operational Program and the Youth Employment Initiative (YEI) 2018. J. Carbajo thanks the financial support by the Government of Spain for a grant under the Juan de la Cierva_Incorporación programme (IJCI-2017- 32682). The authors would like to thank A. Pérez for performing the BET and TGA measurements

Materiales cerámicos tenaces compuestos de mullita-circona

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias. Departamento de Optica y Estructura de la Materia. Fecha de lectura: 26-10-198