Hot corrosion studies of HVOF sprayed carbide and metallic powder coatings on alloy 80A at 900 °c

The current work compares the high temperature corrosion behavior of alloy 80 A coated with carbide (Cr₃C₂-25NiCr) and Metallic (NiCrMoNb) powders through high velocity oxy-fuel (HVOF) process, under 50 cyclic condition at 900 °C. The corrosion study was conducted in the air oxidation environment and molten salt environment. The coating thickness, hardness, and porosity were assessed along the cross section direction. The results of thermogravimetry analysis showed that the substrates subjected to air oxidation environment showed a lesser mass gain, in comparison to its molten salt environment substrates (uncoated and coated substrate) and it trails the parabolic rate law of oxidation. The uncoated substrate had shown excellent corrosion resistance, whereas poor corrosion resistance was observed in the metallic powder coated substrate in the molten salt (Na₂SO₄ + 60% V₂O₅) environment. The existence of MoO₃ phase reduced the corrosion resistance of the metallic powder coated substrate. The existence of NiCr₂O₄ and Cr₂O₃ phases observed on Cr₃C₂-25NiCr coating provided good resistance to hot corrosion in the molten salt environment.