iTSSe TSS ADVANCED MATERIALS & PROCESSES | APRIL 2025 35 iTSSe TSS RESULTS: A LEAP IN COATING QUALITY Microstructural Analysis. Scanning electron microscopy (SEM) represented in Fig. 3 revealed stark differences between coatings deposited using unoptimized and optimized parameters. Coatings from unoptimized trials exhibited porosity, inter-splat cracks, and decarburization, as evidenced by the absence of carbon in energy dispersive spectroscopy (EDS) analyses reported in Table 1. Conversely, optimized parameter coatings displayed dense, crack-free microstructures with carbon levels comparable to the feedstock, confirming limited decarburization. FEATURE Key insights from the framework include: • Oxygen-to-Fuel Ratio: Maintaining a ratio slightly above the stochiometric oxygen levels (3.3) in the flame, ensures e icient burning of the fuel and curbing carbon deposits in the chamber and excessive oxygen in the flame. • Barrel Length: A shorter barrel reduces particle exposure to high temperatures, and reduces overheating and melting of the fine carbides. Figure 2 shows the e ect of particle size and spray parameters on particle velocity and temperature during their in-flight along the barrel length. Based upon the theoretical framework, four parameters were identified and compared against seven randomly selected unoptimized parameters covering the range from low energy to high energy parameters in order to evaluate the efficacy of parameter optimization. The details about the unoptimized and optimized parameters can be found in the detailed version of the work published elsewhere[8]. Fig. 2 — The e ect of particle size and spray parameters on (a) velocity and (b) temperature of the particles during their in-flight inside the barrel. (a) (b) Fig. 3 — SEM analysis of the coatings deposited using randomly selected unoptimized parameters and optimized parameters. UOP=unoptimized parameters, OP=optimized parameters (a) (c) (e) (g) (b) (d) (f) (h) Physical and Mechanical Properties. Optimized coatings demonstrated superior physical and mechanical characteristics: • Porosity: Coatings from optimized trials were markedly less porous due to enhanced particle velocity during deposition. Optimized parameters resulted in least porosity of 0.28 ± 0.2 %, while unoptimized parameters resulted in least porosity of 1.27 ± 0.05 %. • Surface Roughness: Comparable to regular-sized powder coatings, optimized coatings o ered smoother finishes, reducing the need for extensive grinding. The 4
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