Abstract
In-flight particle diagnostics have enhanced our understanding of thermal spraying and improved coating reproducibility. However, no methodology to verify the measured in-flight particle properties has been proposed in the literature yet. This methodology requires describing the entire free jet from accurate measured values. This study deals with a novel method to verify the measured in-flight particle sizes and velocities by estimating the particle mass flow rate (PMFR) in the free jet. To this end, the entire free jet cross section was divided into several non-overlapping focal planes, and the size and velocity of the in-flight particles were measured by optical diagnostics at these focal planes. The PMFR of the powder feeder was used as a reference to validate the determined PMFR in the free jet. The results showed a good agreement with the PMFR of the powder feeder and could be replicated with different feedstock powders, demonstrating the capability of the developed method. Furthermore, the determined PMFR distribution in the entire free jet, referred to as digital footprint, agreed well with the height of the experimental footprints of the spray jet on a substrate. Consequently, it can be concluded that the spatial PMFR distribution was also properly measured.
Highlights
Atmospheric plasma spraying is the most flexible of all thermal spraying technologies, since it can be used in combination with a wide variety of feedstock materials, which can be injected radially or axially in the plasma jet (Ref 1)
This study deals with a novel method to verify the measured in-flight particle sizes and velocities by estimating the particle mass flow rate (PMFR) in the free jet
The PMFR of the powder feeder was used as a reference to validate the determined PMFR in the free jet
Summary
Atmospheric plasma spraying is the most flexible of all thermal spraying technologies, since it can be used in combination with a wide variety of feedstock materials, which can be injected radially or axially in the plasma jet (Ref 1). The carrier gas flow, the particle size distribution of the feedstock material, the injector nozzle diameter and its position as well as the plasma properties control the dispersion of the particles in the plasma jet (Ref 2). The temperature and velocity of the particles vary significantly in the plasma jet, depending whether the particles are in the hot core of the jet or in its relatively cold outer part. Due to this temperature and velocity difference in the free jet, the deposition behavior of the particles on the substrate depends on their individual trajectory (Ref 4). A high deposition efficiency is desirable in many applications for economical reasons
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