En este trabajo se ha estudiado, las fases, las propiedades mecánicas y la resistencia al desgaste abrasivo de recubrimientos cerámicos alumina/titania proyectados por el proceso de oxifuel (spray llama). La proporción de titania tiene una fuerte influencia sobre la porosidad de los recubrimientos, habiéndose observado una disminución casi-lineal de la porosidad con el incremento de titania. Las fases cristalinas que resultan después de la proyección han variado según la naturaleza del polvo y el proceso térmico experimentado. Mientras la dureza obtenida depende sólo del porcentaje en peso de titania, la tenacidad es una función inversa de la dureza, y, la resistencia al desgaste por abrasión es una función creciente con la dureza de los recubrimientos. Palabras clave: Alúmina-titania; recubrimientos cerámicos. spray llama, propiedades mecánicas, desgaste abrasivo. Mechanical and tribological properties of alumina/titania coatings deposited by Ooxifuel.In this paper the porosity, phases, mechanical properties and abrasive wear resistance of ceramic layers of Al 2 O 3 /TiO 2 deposited using the flame spray process are evaluated. The proportion of titania has a strong influence on the porosity of the coating, having observed an approximately linear plot decrease with the increasing of titania´s content. Crystalline phases of the deposited layers changed according to the characteristics of the powder and the thermal process employed. It has been observed that hardness depends only on the titania percentage, also toughness decreases with coatings hardness but resistance to abrasive wear traces an increasing lineal plot with this property.
The growth kinetics of ZnO nanorods were studied by means of an electrochemical deposition process on ITO electrodes submerged in an aqueous solution of 5 mM ZCl+0.1 M KCl at 80 degrees C. The stages of the growth kinetics showed a mechanism of formation of nano-spheres which with time were transformed into hexagonal crystals of ZnO. Cathodic current densities of 0.1 to 1 mAcm2 formed hexagonal columns of 800 nm thickness while stronger currents formed a high-density layer of cylindrical nanorods 80 nm in diameter. An amorphous barrier layer was found between the surface of the electrode and the base of the nano-columns. The conditions assayed showed the possibility of adjusting the morphological characteristics of the layer in order to obtain different properties in different applications.
The oxidation behaviour of alumina/titania (97/3, 87/13 and 60/40) ceramic coatings using a Ni-Al coupling layer was studied in a thermobalance. Both layers were deposited on an AISI 304 stainless steel base metal by the flame spray technique. The coated steel was heated from room temperature to 1,123 K at 40 K min -1 , oxidized in air for 50 h, and then cooled to room temperature at 40 K min -1 . The mass gain was mainly attributed to the oxidation of Ni-Al coupling layer. Kinetic laws, DW·S -1 (mg.mm -2 ) vs. time (hours) were close to a parabolic plot for each sample. Surface composition of ceramic top layer and the cross section of multilayer system were analysed using a wide range of experimental techniques including Scanning Electron Microscopy (SEM), equipped with a link energy dispersive X-Ray spectroscopy (EDX) and X-Ray diffraction (XRD) before and after the oxidation process. Coatings 97/3 and 87/13 presented a stable structure after flame spray deposition and they did not evolve with the oxidation process, while most of the 60/40 coating changed to a metastable structure after deposition and to a more stable structure after oxidation with high micro-cracks content. SEM and EDX microanalysis of the cross-sections showed that significant oxidation and a weak intergranular precipitation had been produced in the coupling layer and on the stainless steel base metal, respectively. ResumenEl comportamiento a oxidación de recubrimientos cerámicos alúmina/titania (97/3, 87/13, 60/40) usando una capa de anclaje Ni-Al se ha estudiado mediante una termobalanza. Ambas capas se han depositado sobre un acero inoxidable AISI 304 utilizando la técnica de proyección llama (FS). El acero recubierto se ha calentado desde la temperatura ambiente hasta 1.123 K a 40 K min -1 , se ha oxidado al aire durante 50 h, y luego se ha enfriado hasta la temperatura ambiente a 40 K min -1 . La ganancia en masa se atribuye a la oxidación de la capa de enganche Ni-Al. La cinética DW·S -1 (mg.mm -2 ) vs. tiempo (horas) se ha ajustado a una ley parabólica para todas las muestras. La composición superficial de la capa cerámica y la sección transversal del sistema multicapa se han analizado mediante las técnicas de Microscopía Electrónica de Barrido (SEM), Espectroscopia de Energías Dispersivas de Rayos X (EDX), Difracción de Rayos X (XRD) antes y después del proceso de oxidación. Los recubrimientos 97/3 y 87/13 han presentado una estructura estable tras el proceso de deposición por proyección por llama y esta estructura tampoco ha evolucionado después de la oxidación, mientras la mayor parte del recubrimiento 60/40 ha cambiado a una estructura metaestable después la deposición y finalmente ha evolucionado a una estructura más estable después de la oxidación con alto contenido de microagrietamiento. El microanálisis mediante SEM y EDX de las secciones transversales han mostrado una oxidación significativa en la capa de enganche y una débil precipitación intergranular en el material base AISI 304. Palabras claveAISI 304; Capa de an...
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