Oxidation resistance of boiler steels with Al2O3-Y2O3 nano- and micro-composite coatings produced by sol-gel process

Al2O3-Y2O3 nano- and micro-composite coatings have been deposited on boiler steel substrates using sol-gel composite coating technology. The processes include dipping samples in a sol-gel solution dispersed with fine ceramic powders, which is prepared by high-energy ball milling. Scanning electron microscopy (SEM) and XRD analyses show that the one-layer coating (i.e. dipping for one time) has a thickness of more than 2 pm. The coating is mainly composed of alpha-Al2O3 and gamma-Al2O3, and is relatively dense without cracking after drying and sintering treatments. The oxidation tests performed in air at 600 degrees C show that the coatings possess much improved resistance to high temperature oxidation and scale spallation. It is believed that the nano-structured composite particles and reactive elements are integrated into the coatings, which played an important role in improving their oxidation resistance.