Thermal shock properties and failure mechanism of plasma sprayed Al2O3/TiO2 nanocomposite coatings

Thermal shock properties and strengthening mechanics of Al2O3/TiO2 nanocomposite ceramic coatings deposited by plasma spraying technology were studied. The results indicate that the thermal shock properties of plasma sprayed nanocomposite ceramic coatings get ahead of that of conventional Al2O3 and Al2O3/TiO2 coatings. Presence of nanophase not only improves matching degrees of thermal propagation coefficient between ceramic coatings and bond-coats or substrates, but also lead cracks in top ceramic coatings to deviate, which could markedly prevent generation and propagation of thermal shock cracks. The study also shows that generation and propagation of thermal shock cracks locate at bond-coat/substrate interface. With the increase of thermal cycles, the thermal shock cracks propagate from bond-coat/TGO interface to top ceramic coat. The thermal shock temperature increase results in the reduction of thermal shock properties. The failure process of thermal shock includes crack initiation, propagation and coating spallation. Bond-coat/substrate interface is one of major factors which lead coatings to spallation failure.