Effect of Particle Size Distribution on Isothermal Oxidation Characteristics of Plasma Sprayed CoNi- and CoCrAlY Coatings

Abstract

The effect of particle size distribution on the degradation behavior of plasma sprayed CoNi-and CoCrAlY coatings during isothermal oxidation was investigated, in terms of the oxygen content, porosity, surface roughness, and oxide scale formation. The results show that the degradation of both coatings was considerably influenced by the starting particle size distribution. It also shows that in the assprayed vacuum plasma spray (VPS) coatings the oxygen content on the coating surface increased significantly with decreased average particle size. But after thermal exposure, the difference of the oxygen contents between the coatings with different particle size was decreased. The powder with various particle size resulted in low porosity inside the coatings during the deposition process. The surface roughness of the coatings increased with increased particle size. The small particles produced a relatively smooth surface, and the oxide growth in the coating deposited by small particle was slower than that in the large particle coating.

Flattening Characteristics of Ni<SUB>20</SUB>Cr Thermal-Sprayed Coating Layers on Preheated SCM415 Substrates

“…In order to study existing conventional flame spray gun equipment, we used a Metco 5P-II and two different nickel-based Ni 20 Cr particles (43F-NS and 43VF-NS, Sulzer Metco Inc.) with mean diameters of 45 mm and 20 mm, respectively, to investigate the particle size effect on flattening characteristics. As shown in Fig.…”

“…10) Composite particles consisting of a solid phase and a metallic binder play an important role in the development of thermally sprayed coatings with increased wear and corrosion resistance. 11) Especially, most of thermal spray processes such as conventional flame spray, HVOF, plasma spray, and cold spray have widely used the Ni or nickel alloy particles (e.g., Ni 20 Cr, NiCrAlY, and NiCoCrAlY) for the surface treatment such as reclamation for a re-work and repair of damaged parts and bond coats. 10,[12][13][14] Therefore, the mechanical, tribological, and thermal properties of the thermal spray coatings were reported in the previous literature.…”

“…In this case, the wetting of molten particles is enhanced during splat flattening, affecting solidification behavior. Seo et al 20) investigated the degradation behavior of sprayed CoNi-and CoCrAlY coatings with different particle sizes by using the vacuum plasma spray. They found that the small particles produced a relatively smooth surface, and as the particle size decreased, the oxide growth in the coating layer was slower compared to those using larger particles.…”

“…Although abundant research 15,[17][18][19][20][21] has been reported, the flattening behavior of thermal-spayed particles on preheated substrates has been still an open point, and there is a lack of information on flattening characteristics, substantially depending on substrates and coating properties. More effort should be made to yield useful experimental and numerical data in establishing greater reliability and controllability of thermal spraying processes for better coating quality and finding optimized procedures.…”

“…More effort should be made to yield useful experimental and numerical data in establishing greater reliability and controllability of thermal spraying processes for better coating quality and finding optimized procedures. Therefore, we report on the flattener characteristics of surface morphology and element distributions of flame-sprayed Ni 20 Cr alloy particles on commercially available SCM415 substrates, widely used in various industrial applications, which are preheated up to 523.15 K. Moreover, we analyze the particle size effect on the flattening characteristics of coating layer by using commercially available two kinds of Ni 20 Cr particles. To analyze the thermal and flow characteristics in a thermal spraying process, we present temperature and velocity distributions of continuous and discrete phases estimated by computational fluid dynamics (CFD) simulations involving the global chemical reaction model.…”