AlPO4-C Composite Coating on Ni-based Super Alloy Substrates for High Emissivity Applications : Experimentation on Dip Coating and Spray Coating

Abstract

High emissivity coating was developed on Ni-based super alloy substrates by dip coating and spray coating technique using a chemical precursor sol. The coating material was characterised thoroughly by XRD, SEM, TEM and XPS analyses. Characterisation results showed the presence of nano carbon in the AlPO4 matrix which imparted high emissivity to the coating. Emissivity of the coating varied from 0.6 to 0.9 in the wave length range : 2 µm - 25 µm depending on the thickness of the multilayered coating. Spray coating was very effective for coating the bigger substrates and TPS panels. Emissivity offered by the spray coated substrates was little lower compared to the dip coated substrates. Emissivity offered by the spray coated substrates was little lower compared to the dip coated substrates. Cyclic oxidation performances of the coated substrates at 800 °C and 1000 °C for 100 hrs of thermal exposure were recorded and compared with that of the bare substrate. The emissivity coating was found to offer substantial oxidation resistance to the base substrate at high temperatures.