Optimization of wetting behavior in plasma-sprayed Fe-based amorphous/crystalline coatings resulting improved corrosion inhibition ability

The present study is focused on understanding the influence of varying plasma spray parameters, viz., plasma power (20 to 40 kW) and coating thickness on the wetting behavior of atmospheric plasma sprayed (APS) Fe based glassy coatings (Fe₅₇Cr₉Mo₅B₁₆P₇C₆, at. %). The correlation between wetting behavior and the corrosion prevention ability of the coatings in 3.5 wt% NaCl solution has been explored. Microstructural and surface topographical investigation established that spraying parameters significantly affected coating porosity, surface roughness and crystalline phase content. Increase in plasma power along with the coating thickness resulted in lower porosity, reduced surface roughness and increased devitrification. For the coatings deposited with lower thickness, contact angle decreased with increase in plasma power from 20 to 30 kW due to lower surface roughness, which improved wettability. However, with further increase in plasma power, contact angle actually increased due to reduced porosity content, and small pore size, preventing liquid spreading. On the contrary, coating deposited at higher thickness, showed an increasing trend of contact angles with plasma power attributed to the dominance of lower capillary action due to reduction in both pore size and porosity content, in spite of decreased surface roughness. Potentiodynamic polarization experiments showed that the higher thickness (425 ± 25 μm) coating deposited at lower plasma power (20 kW) was least susceptible to corrosion, attributed to its optimum level of porosity content, pore size, hydrophobicity and crystallinity.