Search Results (3)

This study employs computational fluid dynamics (CFD) to analyze the in-flight dynamics of particles in an Ar–H₂ atmospheric plasma spray (APS) torch with a modified diverging-type nozzle. The focus is on optimizing injection parameters—plasma gas flow rates, input power, and carrier gas flow rates—to enhance coating microstructure and deposition efficiency by achieving superheated molten metal droplets. Using a discrete phase model, the heat and momentum transfer of Ni/Al/C (2 wt.% diamond) composite powders (30–110 µm) within the plasma jet were simulated. Results show that particle characteristics, such as temperature and oxidation, can be controlled by adjusting plasma jet temperature (T∞) and velocity (U∞). Smaller particles heat faster, reaching higher temperatures with increased evaporation and oxidation rates. The modified nozzle enables Ni-based alloy particles to reach ~2500 °C, reducing oxygen inclusion in the plasma jet core. This setup allows for the control of the onset of carbon and oxygen reactions, wherein carbon serves as a sacrificial element, protecting the base alloy elements (such as aluminum) from excessive oxidation. Full article

Suspension plasma spraying (SPS) is an effective technique to enhance the quality of the thermal barrier, wear-resistant, corrosion-resistant, and superhydrophobic coatings. To create the suspension in the SPS technique, nano and sub-micron solid particles are added to a base liquid (typically water or ethanol). Subsequently, by using either a mechanical injection system with a plain orifice or a twin-fluid atomizer (e.g., air-blast or effervescent), the suspension is injected into the high-velocity high-temperature plasma flow. In the present work, we simulate the interactions between the air-blast suspension spray and the plasma crossflow by using a three-dimensional two-way coupled Eulerian–Lagrangian model. Here, the suspension consists of ethanol (85 wt.%) and nickel (15 wt.%). Furthermore, at the standoff distance of 40 mm, a flat substrate is placed. To model the turbulence and the droplet breakup, Reynolds Stress Model (RSM) and Kelvin-Helmholtz Rayleigh-Taylor breakup model are used, respectively. Tracking of the fine particles is continued after suspension’s fragmentation and evaporation, until their deposition on the substrate. In addition, the effects of several parameters such as suspension mass flow rate, spray angle, and injector location on the in-flight behavior of droplets/particles as well as the particle velocity and temperature upon impact are investigated. It is shown that the injector location and the spray angle have a significant influence on the droplet/particle in-flight behavior. If the injector is far from the plasma or the spray angle is too wide, the particle temperature and velocity upon impact decrease considerably. Full article

In order to achieve better knowledge of the thermal barrier coatings (TBCs) by supersonic atmospheric plasma spraying (SAPS) process, an experimental study was carried out to elaborate the physicochemical properties of particles in-flight during the SAPS process. One type of commercially available agglomerated and sintered yttria-stabilized-zirconia (YSZ) powder was injected into the SAPS plasma jet and collected by the shock chilling method. The YSZ particles’ in-flight physicochemical properties during the SAPS process, including melting state, morphology, microstructure, particle size distribution, element composition changes, and phase transformation, have been systematically analyzed. The melting state, morphology, and microstructure of the collected particles were determined by scanning electron microscopy (SEM). The particle size distribution was measured by a laser diffraction particle size analyzer (LDPSA). Element compositions were quantitatively analyzed by an electron probe X-ray microanalyzer (EPMA). Additionally, the X-ray diffraction (XRD) method was used to analyze the phase transformation. The results showed that the original YSZ powder injected into the SAPS plasma jet was quickly heated and melted from the outer layer companied with breakup and collision-coalescence. The outer layer of the collected particles containing roughly hexagonal shaped grains exhibited a surface texture with high sphericity and the inside was dense with a hollow structure. The median particle size had decreased from 45.65 to 42.04 μm. In addition to this, phase transformation took place, and the content of the zirconium (Zr) and yttrium (Y) elements had decreased with the evaporation of ZrO₂ and Y₂O₃. Full article