Publication

Abstract : The study investigates the high-temperature corrosion behaviour of Ni–Al coatings produced by the wire arc spraying technique on ASME SA T23 low alloy ferritic tube weldments prepared by shielded metal arc welding. The oxidation tests were conducted on coated and uncoated base metal and welded specimens at 900 °C. The samples were exposed to three salt mediums: a) 80% Flyash + 10% Na2SO4 + 10% V2O5, b) 80% flyash + 10% Na2SO4 + 10% V2O5 and c) 80% Flyash + 10% KCl + 10% NaCl at 900 °C for 100 h. The performance of the coatings was assessed by recording the weight variations and corrosion rate. The surface morphology of the corroded surface was analysed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. The results indicated significant improvement in the high-temperature corrosion resistance of Ni–5Al coated T23 weldment compared to the uncoated counterpart. In the presence of 80% Flyash + 10% Na2SO4 + 10% V2O5 medium, the coated samples exhibited a weight gain of 163%, whilst in the presence of 80%Flyash + 10% Na2SO4 + 10% NaCl, 22.84% weight gain was observed. Similarly, the Ni–5Al coated base metal also exhibited a weight gain of 102% in 80% flyash + 10% Na2SO4 + 10% V2O5 medium and 42% in 80% flyash + 10% Na2SO4 + 10% NaCl. Conversely, 80% Flyash + 10% KCl + 10% NaCl medium showed a weight loss of 105.34% in Ni–5Al coated base metal and 114% in the weld bead. SEM micrographs revealed a severe corrosion rate in uncoated samples due to the non-protective layer's scaling, spalling and deposition. EDS analysis showed the presence of SiO2 and Al2O3 as protective layers in an aggressive molten salt environment in Ni–5Al-coated specimens. This work has applications in fields where corrosion resistance is crucial for maintaining the reliability and safety of machinery exposed to high temperatures, such as coal-fired boilers.