Effects of Surface Chemistry on Splat Formation During Plasma Spraying

Abstract

Ni-Cr single splats were plasma-sprayed at room temperature onto aluminum and stainless steel substrates, which were modified by thermal and hydrothermal treatments to control the oxide surface chemistry. The proportions of the different splat types were found to vary as a function of substrate pretreatment, especially when the pretreatment involved heating. It was observed that surface roughness did not correlate with changes in splat morphology. Substrate surfaces were characterized by X-ray photoelectron spectroscopy using in situ heating in vacuum to determine the effect of thermal pretreatment on substrate surface chemistry. It was found that the surface layers were composed primarily of oxyhydroxides. When the substrates were heated to 350°C, water vapor was released from the dehydration of oxyhydroxide. Preheating the substrate can remove the water prior to spraying: preheated substrates had improved the physical contact between the splat and substrate, which enhanced the formation of disk splats and increased the number of splats.

Ethylene Methacrylic Acid (EMAA) Single Splat Morphology

“…The surface condition [7][8][9][10] and the wettability of the substrate play an important role in the morphology of splats [11]. There are three factors affecting the wettability of the substrate.…”

Spreading Behavior and Morphology of Ethylene Methacrylic Acid (EMAA) Deposits via the Flame Spray Process

“…The amount and the size of the blow holes in Figure 7e are greater than those in Figure 7f due to the greater temperature of the melting droplet of EMAA in Figure 7e compared with Figure 7f. The trapped gas may result from (i) decomposition of EMAA under the spray conditions and/or (ii) gas release from the substrate due to input heat from the particle on impact, as studied by Tran [8,9] who researched aluminum and stainless steel substrates. It is deduced that mild steel would exhibit similar behavior since it is more readily oxidized and, therefore, has an enhanced ability to absorb condensates.…”

“…Therefore, in instances where splats are the preferred morphology then the mild steel substrate should be preheated [1,19,31]. Gas release from the substrate due to input heat from the particle at impact [8,32] is another mechanism that gives rise to splashing.…”

“…The surface condition [7][8][9][10] and the wettability of the substrate plays an important role on the morphology of splats [11]. There are three factors affecting the wettability of the substrate.…”

Effect of the powder deposition rate on the mechanical properties and the structure of the APS-NiCr/Al coating

“…Priroda i količina oslobođenih gasova zavisi od hemijskog sastava površine osnove na koju se nanosi prevlaka [4]. Prisustvo oslobođenih gasova i vodene pare utiče na formiranje pora u slojevima i na granici između prevlake i osnove, a uz prisutnu oksidaciju pospešuju i formiranje oksida kao što je NiO [5,6]. Od oksida hroma u većini slučajeva je prisutan oksid Cr 2 O 3 kao tanak sloj na površini NiCr lamela, a mnogo ređe je prisutan oksid tipa CrO 3 [5].…”