Evaluation of Hot Corrosion Resistance of Stellite 6 Coating Applied on Stainless Steel 17-4ph by a Laser Cladding Method

Fuel and combustion products in a gas turbine can contain impurities of sodium, sulfur, vanadium, silicon, and possibly lead and phosphorus. It increases hot corrosion in the long term. Coatings are often used on gas turbine components to limit surface degradation and obtain precise lifetimes. This research was conducted to investigate the laser cladding on the hot corrosion resistance of the stellite 6 coating created on 17-4PH stainless steel. To achieve the optimal coating parameters, different rates of scanning speed, powder feeding rate, and laser power were investigated. The hot corrosion test was performed by Na2SO4-60%wtV2O5 salt at 900˚C for ten hours. A scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) and X-ray diffraction pattern (XRD) was used for microstructural, elemental, and phase characterization. The superior performance of the stellite 6 cladding can be attributed to the continuous and protective thin oxide region of CoO, Cr2O3, and SiO2 formed on the surface. The coating area below the narrow oxide area was partially oxidized. 17-4PH stainless steel showed less weight gain than the coated sample. However, during the test, destruction, and spraying of the surface of uncoated samples were observed. Even after ten cycles of hot corrosion, the dense and non-porous cover of stellite 6 shows that it has a much higher resistance to hot corrosion compared to the steel substrate.