PSI - Issue 71

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

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1. Introduction Fe-based metallic glass alloys have emerged as a focus of interest for safeguarding structural components in harsh conditions because of their exceptional mechanical and anti-corrosion characteristics (Suryanarayan et al., 2013; Souza et al., 2016). However, the lack of plasticity in Fe-based monolithic metallic glass at room temperature is a huge concern, because it limits their practical engineering applications. To address this issue, the synthesis of in-situ composite structures (glassy matrix embedded in secondary crystalline phases) has gained huge attention for industrial applications (Kumar et al. 2019; Nayak et al., 2019). The development and application of Fe-based amorphous and nanocrystalline coatings onto substrates are ongoing efforts to address the inherent brittleness of Fe-based metallic glasses. These coatings, with thicknesses ranging from tens to hundreds of micrometres, retain the beneficial properties of the metallic glass, such as high hardness and corrosion resistance, while mitigating brittleness. This makes metallic glass coatings more suitable for demanding industrial applications, such as power generation, automotive manufacturing, shipbuilding, and nuclear engineering. The incorporation of alloying elements significantly enhances the properties and extends the lifespan of Fe-based metallic BMGs. In particular, the addition of elements like Al, Ni, Cr, Mo, P, Co, and Y boosts the corrosion resistance of these materials. However, increasing the amounts of Cr (≥15 at.%) and Mo (≥14 at.%) can escalate material costs, which may limit their use in industrial settings (Kumar et al., 2019; Kumar et al., 2020). To address this challenge, cost-effective elements such as Si, C, and B are employed in developing Fe-based nanocrystalline/amorphous composites, which showcase impressive mechanical properties and enhanced corrosion resistance (Suryanarayan et al., 2013; Souza et al., 2016). In this regard, atmospheric plasma spraying (APS) has attracted considerable interest from both industrial sectors and academic research (Liu et al., 2009), primarily because of its straightforwardness and affordability in producing composite coatings (amorphous or nanocrystalline). This approach is especially beneficial for Fe-based metallic glass coatings with ordinary glass forming ability (GFA). In this process, the rapid cooling rate ( ∼ 10 5 – 10 7 K/s) of the splat structure prevents extensive diffusion, promoting the retention of the amorphous phase. In the present work, coatings were deposited using atmospheric plasma spraying at plasma power levels of 25, 30, and 35 kW to investigate the influenc e of coatings’ microstructure on their corrosion behavior in saline environments. Experimental procedure: The coatings were developed using gas-atomized Fe-based fully amorphous feedstock powder with composition of Fe 73 Cr 2 Si 11 B 11 C 3 (at. %) onto a mild steel base (measuring 100mmCompany Pvt. Ltd., India) was used to deposit coatings onto mild steel substrates at spraying parameters mentioned in Table 1. The microstructural studies of powders and coatings were examined using a scanning electron microscope (SEM, SUPRA 40, Carl Zeiss AG, Germany), known for its high resolution and broad depth of field. For porosity evaluation, we selected SEM images of the polished top surface of the coating magnified at 500 X. To analyze the phases present in the as-sprayed coatings and powders, X-ray diffraction (XRD, Rigaku Smartflat, Japan, Cu-K α radiation) was utilized, scanning from a 2θ range of 30° to 110°. Electrochemical analysis of the coating was conducted using a 3.5 wt.% NaCl solution, aimed at examining its corrosion performance. Electrochemical Impedance Spectroscopy (EIS) tests were carried out at a sinusoidal amplitude of 10mV (rms) in the frequency range of 100 kHz to 0.01Hz with 10 points per frequency decade. Raman spectroscopic (S52L, Nost. Co. Ltd, Korea) analysis was performed with a Cobalt laser with a 532nm Wavelength of 200-1400nm on the corroded surfaces following electrochemical polarization to investigate the oxidation products. Surface analysis was also conducted to examine the formation of oxides that developed as a result of the potentiodynamic polarization process. 2.