Knowledge Concerning Splat Formation: An Invited Review

Fauchais, Pierre; Fukumoto, Masahiro; Vardelle, Armelle; Vardelle, Michel

doi:10.1361/10599630419670

Cited by 428 publications

(247 citation statements)

References 79 publications

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“…When metal surfaces are preheated over the transition temperature ( Ref 4,5,10,13,25,26,30,37,38,40,43,52,56,[60][61][62][63][64][65][66] or treated with laser energy densities high enough to modify the oxide layer (Ref 17,20,58), the surface is changed. In addition to desorbtion of adsorbates, the oxide layer composition, thickness and roughness is modified.…”

Section: Substrate Surface Modificationsmentioning

confidence: 99%

Formation of Solid Splats During Thermal Spray Deposition

2009

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This paper reviews the findings of recent research on the formation of solid splats by the impact of thermal spray particles on solid substrates. It discusses methods of describing the substrate, by characterizing both chemical (oxide layers) and physical (surface topography, adsorbed and condensed contaminants) aspects. Recent experiments done to observe impact of thermal spray particle are surveyed and techniques used to photograph particle impact and measure cooling rates described. The use of numerical modeling to simulate impact and deformation of impacting particles is appraised. Two different break-up mechanisms are identified: solidification around the edges of splats; and perforations in the interior of thin liquid films created by droplet spreading without solidification. These two modes can be reproduced in numerical models by varying the value of thermal contact resistance between the splat and substrate. A simple criterion to predict the final splat shape is presented.

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Section: Substrate Surface Modificationsmentioning

confidence: 99%

Formation of Solid Splats During Thermal Spray Deposition

2009

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“…As a result, the eventual shape of the drop is a "pancake" of uniform thickness except at the rim, where surface tension effects are significant. The thickness of the pancake is simply the height where the drop surface first collides with the boundary layer.The impact of a liquid drop onto a dry solid surface lies at the heart of many important technological processes [1,2], from the application of a thermal spray [3,4,5,6,7,8,9] to atomization of fuel in a combustion chamber [8,10,11,12]. Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16].…”

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confidence: 99%

Impact of a Viscous Liquid Drop

et al. 2010

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We simulate the impact of a viscous liquid drop onto a smooth dry solid surface. As in experiments, when ambient air effects are negligible, impact flattens the falling drop without producing a splash. The no-slip boundary condition at the wall produces a boundary layer inside the liquid. Later, the flattening surface of the drop traces out the boundary layer. As a result, the eventual shape of the drop is a "pancake" of uniform thickness except at the rim, where surface tension effects are significant. The thickness of the pancake is simply the height where the drop surface first collides with the boundary layer.The impact of a liquid drop onto a dry solid surface lies at the heart of many important technological processes [1,2], from the application of a thermal spray [3,4,5,6,7,8,9] to atomization of fuel in a combustion chamber [8,10,11,12]. Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16]. These results are motivating new studies on the large-scale deformations created by impact when air effects are absent as well as how a splash forms [17,18,19,20,21,22,23].Here we focus on the impact of a viscous liquid drop when air effects are absent. Recent experiments show that reducing the ambient gas pressure also suppresses the splash of a silicone oil drop. However, the form of the splash is very different. While the splash from a lowviscosity liquid develops within a few 10 µs of impact, the splash from a silicone oil develops slowly, becoming evident only after most of the liquid drop has fallen and flattened into a thin pancake [24,25]. We use an axisymmetric Volume-of-Fluid (VOF) code to simulate the impact at reduced ambient pressure [26,27,28]. Our results show that a boundary layer, corresponding to a thin region where the radial flow created by impact adjusts to the no-slip condition at the wall, is created by the impact. The boundary layer has uniform thickness. As impact nears its end, the drop surface flattens onto the boundary layer, evolving into a pancake of uniform thickness.The Volume-of-Fluid simulation solves the NavierStokes equations, together with constraint of incompressibility, for both the liquid interior and the gas exterior at reduced pressure. Physically appropriate boundary conditions, in particular the Laplace pressure jump across the surface due to surface tension, are enforced [26]. In a typical run, an initially spherical liquid drop with radius a collides with a dry, smooth solid surface at an impact speed U 0 of several m/s. The ambient air density ρ g is kept so small that 2-fold changes in in the value of ρ g have little effect on the liquid dynamics. The bottom surface of the liquid drop is not broken upon impact, which corresponds to maintaining an apparent contact angle of 180 • where the liquid rim meets the wall (Fig. 2a) [29]. We require that the velocity field inside the drop satisfies both the no-flux an...

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“…Although the behavior of high energy density plasma at the pressures associated with VLPPS is not well understood, it has been reported that heat transfer is no longer collision dominated in these lower pressure regimes [2,[29][30][31][32][33]. Complex interactions exist between the feedstock material and the VLPPS plasma, most of which can currently only be inferred based on plasma spray research at higher pressures [34][35][36][37]. If very fine powder (<15 microns) is injected into the plasma jet at very low pressures, the small particles tend to follow expansion of the jet and distribute across the plume.…”

Section: Plasma Jet Properties At Very Low Chamber Pressuresmentioning

confidence: 99%

Very Low Pressure Plasma Spray—A Review of an Emerging Technology in the Thermal Spray Community

et al. 2011

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Abstract:A fundamentally new family of thermal spray processes has emerged. These new processes, collectively known as very low pressure plasma spray or VLPPS, differ from traditional thermal spray processes in that coatings are deposited at unusually low chamber pressures, typically less than ~800 Pa (6 Torr). Depending upon the specific process, deposition may be in the form of very fine molten droplets, vapor phase deposition, or a mixture of vapor and droplet deposition. Resulting coatings are similar in quality to coatings produced by alternative coating technologies, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), but deposition rates can be roughly an order of magnitude higher with VLPPS. With these new process technologies modified low pressure plasma spray (LPPS) systems can now be used to produce dense, high quality coatings in the 1 to 100 micron thickness range with lamellar or columnar microstructures. A history of pioneering work in VLPPS technology is presented, deposition mechanisms are discussed, potential new applications are reviewed, and challenges for the future are outlined. OPEN ACCESSCoatings 2011, 1 118

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Knowledge Concerning Splat Formation: An Invited Review

Cited by 428 publications

References 79 publications

Formation of Solid Splats During Thermal Spray Deposition

Formation of Solid Splats During Thermal Spray Deposition

Impact of a Viscous Liquid Drop

Very Low Pressure Plasma Spray—A Review of an Emerging Technology in the Thermal Spray Community

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