Improved Protection Properties by Using Nanostructured Ceramic Powders for HVOF Coatings

Abstract

The potential of the high-velocity oxy-fuel (HVOF) thermal spray process for reduced porosity in coatings compared to those produced by other ambient thermal spray processes is well known. The ability to produce high-density ceramic coatings offers potential in high-performance applications in the field of wear, corrosion resistance, and dielectric coatings. However, due to operational limit of the HVOF process to effectively melt the ceramic particles, the process-structure relationship must be well optimized. It has been also demonstrated that benefits from HVOF ceramic coatings can be obtained only if particles are melted enough and good lamella adhesion is produced. One strategy to improve melting of ceramic particles in relative low-flame temperatures of HVOF process is to modify particle crystal structure and composition. In this paper the effect of the powder manufacturing method and the composition on deposition efficiency of spray process as well as on the mechanical properties of the HVOF sprayed are studied. Effect of fuel gas, hydrogen vs. propane, was also demonstrated. Studied materials were alumina-, chromia-, and titania-based agglomerated powders. Coating properties such as microstructure, hardness, abrasive wear resistance, and relative fracture toughness were compared to the coating manufactured by using conventional fused and crushed powders. It can be concluded that powder size distribution and microstructure should be optimized to fulfill process requirements very carefully to produce coatings with high deposition efficiency, dense structure, improved fracture toughness, and adhesion.

Crystalline ytterbium disilicate environmental barrier coatings made by high velocity oxygen fuel spraying

“…In a recent work Bakan et al 9 demonstrated that YbDS coatings with porosities below 10% and relatively high crystallinity of more than 30% could be produced by high velocity oxygen fuel spraying (HVOF). This is in accordance to prior works where coatings from ceramic materials such as alumina, chromia, titania, or even hydroxyapatite with high degrees of crystallinity and high phase purity could be achieved by HVOF deposition starting from small-sized or nano-agglomerated feedstocks [10][11][12][13] . All studies concluded that dense ceramic coatings can be obtained with sufficient deposition efficiency only if particles are melted sufficiently so that good adhesion between the deposited splats is achieved, while crystallinity in the coating depends mainly on the amount of partially unmelted powder particles.…”

Wettability of hierarchically-textured ceramic coatings produced by suspension HVOF spraying

“…20 However, attempts to deposit nanofeatured coatings using HVOF have been hampered by the need to obtain sufficient particle soening to successfully form a coating, whilst still retaining the nano-structure within the original powder particles. 21 These attempts were aimed at obtaining coatings with novel tribological properties, rather than superhydrophobicity. In conventional powder feeding, a reduction of the particle size below 5 mm requires specialised powder feeding methods due to the poor owability of such feedstocks, which results from strong agglomeration between particles.…”

Abrasion, Erosion and Cavitation Erosion Wear Properties of Thermally Sprayed Alumina Based Coatings

“…As a down side, the added TiO 2 also decreases hardness and wear resistance of the coating [2]. During the last decade, nanostructured powders have been gaining increasing attention and improved coating properties, e.g., higher toughness, adhesion, and wear resistance, have been reported [4][5][6][7][8]. Typically, Al 2 O 3 and Al 2 O 3 -TiO 2 powders have been manufactured by blending Al 2 O 3 and TiO 2 fused and crushed powders or by cladding Al 2 O 3 particles with TiO 2 .…”

“…During recent years, the coating properties have been improved by the use of HVOF processes, as well as with the development of nanostructured powders for plasma spraying, i.e., agglomerated and sintered powders from nanosized primary particles. Both, nanostructured coatings and HVOF-sprayed coatings have been reported to possess significantly higher wear resistance compared to conventional plasma-sprayed coatings [4][5][6][7][8]18,19]. However, the performance of nanostructured plasma-sprayed coatings and HVOF-sprayed ceramic coatings has not been truly compared under abrasive, erosive, and cavitation erosion wear.…”