PSI - Issue 71

Ritik K. Nakhate et al. / Procedia Structural Integrity 71 (2025) 357–363

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Table 1. Factors utilized for applying Fe-based nanocrystalline/ amorphous coatings through Atmospheric Plasma Spraying (APS) Coating 1 Coating 2 Coating 3 Powder feed rate 40 g/min 40 g/min 40 g/min Plasma Power 25 kW 30 kW 35 kW Coating Thickness ~ 100 ± 20 μ m

3. Results and Discussion: 3.1. Characterization of powders

Fig. 1a displays the morphology of powders utilized in (APS), showing a size distribution ranging from 5 to 70 μm with an average particle (100 mm × 2 mm). This composition was chosen based on its high glass forming ability (GFA) and relatively inexpensive alloying elements (Kumar et al., 2019). A commercial plasma spray torch (Plasma F-4, Metallizing Equipment le size of 25 μm, primarily spherical in form; this diverse particle size distribution enhances corrosion and mechanical properties, as coarser powders lead to improved corrosion resistance and higher amorphous phase retention, while finer powders yield denser microstructures and better mechanical attributes, with XRD analysis confirming a fully amorphous phase (Fig. 1b) due to the high glass-forming ability of the alloy i.e. Fe 73 Cr 2 Si 11 B 11 C 3 (at. %) (An et al., 2014, Kumar et al., 2019).

Fig. 1. (a) SEM image displays Fe-based feedstock powder with a spherical shape, while (b) XRD pattern shows a broad and hollow peak indicative of its amorphous nature.

3.2. Coating microstructure and phase evolution Fig. 2 displays the morphology of coatings sprayed onto the substrate at different plasma power levels. The coating deposited with the lowest plasma power (25 kW, Coating 1) exhibits a significant presence of partially molten particles (Fig. 2a). As the plasma power increases, a reduction in partially melted particles becomes evident (Fig. 2b and c). From the SEM images of the cross-sections of plasma-sprayed coatings (shown in figures 2d-f), it was found that with pore volume fraction decrease at elevated plasma power i.e. porosity content in Coating 1 was ~10 Vol. %, Coating 2 was ~ 8 Vol. % and Coating 3 was ~5 Vol. %). This was ascribed to the fact that the molten particles that are sprayed onto the previously deposited splat layers fill the available porosities. Moreover, heat accumulation from splat stacking promotes fusion, resulting in well-adhered splats (An et al., 2014; Kumar et al., 2019). X-ray diffraction analysis of plasma- sprayed coatings shows a broad hump (2θ=45 – 60°) with distinct crystalli ne peaks attributed to α -Fe, as illustrated in Fig. 3, with the amorphous phase content decreasing variably with increased plasma power due to higher heat input and greater heat accumulation. The amorphous content estimated based on the XRD peaks intensity (Kumar