Influence of the feedstock characteristics on the microstructure and properties of Al2O3–TiO2 plasma-sprayed coatings

Abstract

Atmospheric plasma spraying (APS) is an interesting technique to obtain nanostructured coatings due to its versatility, simplicity and relatively low cost. However, nanometric powders can not be fed into the plume using conventional feeding systems, due to their low mass and poor flowability, and must be adequately reconstituted into sprayable micrometric agglomerates.In this work, Al 2 O 3 -13wt%TiO 2 nanostructured and submicron-nanostructured powders were deposited using APS. The feedstocks were obtained by spray drying from two starting suspensions, prepared by mixing two commercial nanosuspensions of Al 2 O 3 and TiO 2 , or by adding nanosized TiO 2 and submicron-sized Al 2 O 3 powders to water. The spray-dried granules were heat-treated to reduce their porosity and the resultant powders were fully characterised.Optimisation of the deposition conditions enabled the reconstituted powders to be successfully deposited, yielding coatings that were well bonded to the substrate. The coating microstructure, characterised by SEM, was formed by semi-molten feedstock agglomerates surrounded by fully molten particles that act as a binder.Moreover, microhardness, adhesion, and tribological behaviour were determined, and the impact of the granule characteristics on these properties was studied. It was found that changing the feedstock characteristics allows to control the coating quality and properties.2

Atmospheric plasma spraying coatings from alumina–titania feedstock comprising bimodal particle size distributions

“…This is particularly interesting for alumina suspension due to the intrinsic difficulties associated with the preparation of concentrated nanoparticle suspensions of alumina as reported elsewhere [11]. The relationship between these improved agglomerate feedstock characteristics and the final coating properties has been scarcely treated in the literature [10]. In this respect, we have also recently reported improved photocatalytic activity in APS TiO 2 coatings when using a mixture of nano and submicrometric particles in the spray-dried feedstock.…”

“…The increased wear resistance of coatings obtained from nanostructured feedstocks in comparison with conventional (obtained from micrometric powders) coatings has been extensively reported in the recent literature [10,16,18,21]. The reasons showed in the literature for explaining this behaviour are as follows: the toughening contribution of the partially molten nanostructured zones [18,23,24] (not seen in this work), a more homogeneous TiO 2 distribution inside the splats leading to higher splat bonding strength [5,16] and the role of different additives such as CeO 2 and ZrO 2 added to the composition [25].…”

“…submicronnano sized particles. The use of a bimodal distribution of submicron-nano particles, comprising the precursor suspension of the spray-dried powder, can give rise to significant benefits during the suspension processing, i.e higher solids content and lower viscosity leading to better properties in the resulting feedstock agglomerates, such as higher agglomerate bulk density and improved powder flowability [9,10]. This is particularly interesting for alumina suspension due to the intrinsic difficulties associated with the preparation of concentrated nanoparticle suspensions of alumina as reported elsewhere [11].…”

Effect of particle size on processing of bioactive glass powder for atmospheric plasma spraying

“…Hausner ratio represents a method to estimate the flowability-cohesiveness of a given powder. Due to its simplicity HR has been extensively used to characterise APS feedstocks [16,17]. HR is defined as the quotient of the tapped density to the bulk (or poured) density of the powder.…”

Influencia de los parámetros de proyección por plasma atmosférico en recubrimientos de YSZ obtenidos a partir de polvos micro y nanoestructurados

“…La sección transversal de los recubrimientos se observó mediante micrografías MEB y se determinó el porcentaje de área de poros y zonas infundidas mediante análisis de imagen a partir de 10 micrografías MEB a 500x (15). La microdureza y tenacidad de los recubrimientos se obtuvieron con el equipo LECO M400 (Leco Co., EEUU).…”