Effect of Structure Density of Milled Powder on Hot Corrosion and Erosion Resistance of HVOF-Sprayed Cr₃C₂-NiCr Coating

The present study investigated the effect of mechanical milling on Cr₃C₂-NiCr coatings deposited using the HVOF spraying method. The milling process was carried out using powder with varying characteristics to produce fine-grained and flaky powders. The milled powder coatings exhibited higher density and reduce porosity, leading to improve surface hardness and bond strength. To evaluate the performance of these coatings, hot corrosion and erosion tests were conducted under controlled conditions. The hot corrosion test was performed in a chloride environment using a vapor-condensed salt mixture (45% NaCl + 55% KCl) at 600 °C for 100 hours, while the erosion test was conducted at room temperature with an impact angle of 90°. The results showed that the milled powder coating demonstrated superior resistance to both corrosion and erosion compared to the unmilled powder coating. Specifically, the corrosion mass product and erosion rate of the milled powder coating were 3.40 mg/cm² and 0.62 mg/g, respectively, while those of the unmilled powder were 10.07 mg/cm² and 1.84 mg/g, respectively. This study revealed that the microstructure of powder coating has a significant effect on its erosion and hot corrosion performance. Furthermore, the research investigated the mechanisms responsible for these performances and concluded that the coating’s porosity and homogeneous structure can enhance its resistance against both erosion and corrosion.