A Comparative Microstructural Investigation of Nanostructured and Conventional Al2O3 Coatings Deposited by Plasma Spraying

Abstract

Nanostructured and conventional Al 2 O 3 powders have been plasma sprayed to produce coatings. The parameters for retaining a fraction of the nanostructure were investigated. Dissimilarities were observed between the two types of coating, regarding properties and phase proportions, which are related with the different percentages of semimolten particles in the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings owing to the higher porosity of the nanoparticle agglomerates. The molten part of both conventional and nanostructured coatings consisted of c-Al 2 O 3 of columnar morphology. In order to investigate the mechanism of the melting front advance into the particle interior, the particles were sprayed directly into deionized water. The nanoparticles mainly formed hollow spheres, whereas the conventional particles mainly formed compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating porosity and, consequently, coating properties such as hardness, adhesion, and surface roughness, was linked to the hollow sphere phenomenon.

Wear Behavior Analysis of Al2O3 Coatings Manufactured by APS and HVOF Spraying Processes Using Powder and Suspension Feedstocks

“…Moreover, the much smaller size of splats and pores means that the indent spans several splats. This phenomenon [56] could decrease the real microhardness value (see Figure 5), but it is still in accordance with the literature [32]. The highest values of microhardness were obtained for S-HVOF coating.…”

Axial Plasma Spraying of Mixed Suspensions: A Case Study on Processing, Characteristics, and Tribological Behavior of Al2O3-YSZ Coatings

“…A sharp increase in the number of recent studies on the subject reflects the growing interest in the deposition of fine-structured coatings (i.e., with submicron and nano-sized features) with enhanced functional performance in terms of wear, erosion, thermal barrier properties, etc. compared to corresponding conventional coarse-structured coatings [2][3][4][5][6][7][8][9][10]. One of the most desirable routes for the production of such coatings involves thermal spraying of fine (submicron and nano-sized) particles.…”

Preparation and characterization of highly amorphous HVOF stainless steel coatings

“…NS 2 coating presents the lowest porosity due to the highest melting degree achieved at the highest particle temperatures. At high particle temperatures, molten material of high diffusivity fills the asperities and gaps of the previously deposited layers, leading to low porosities [21]. All the coatings present similar hardness values, which are substantially higher than the ones reported for stainless steel 304s [8] and stainless steel thermally sprayed coatings [3].…”