Papers by Author: Ping Xiao

Abstract: The constrained sintering behavior of yttria stabilized zirconia coatings containing 1 wt. % alumina produced using electrophoretic deposition has been studied. Coatings have been characterized by scanning electron microscopy, micro-hardness and fluorescence spectroscopy after sintering in air at 1100°C and 1200°C. These coatings were compared with those that additionally contained 1 wt. % soda-lime glass. Micro-hardness and fluorescence spectroscopy are shown to accurately monitor the density of the coatings. Fluorescence spectroscopy showed that the density across the coating is even, as expected from modelling literature. The addition of 1 wt. % of soda-lime glass is shown to improve the sintered density of coatings.

Abstract: Yttria stabilized zirconia (YSZ) particle suspension in acetylacetone (ACAC) was deposited onto Fecralloy substrates by using EPD and then constrained sintered at 1200°C. Before EPD, the operational pH value of the suspension was adjusted with addition of acetic acid or base triethanolamine (TEA). The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure. Results showed that the zeta potential decreased to close to zero with the increase of pH value from 4.4 to 7.4, then increased with further increase of the pH. This ‘U’ shape zeta potential-pH relationship was probably resulted from the adsorption of TEA. This reduced the degree of particle coagulation and increased the packing density of the EPD coatings; therefore, promoted the sequent sintering of coatings which was evaluated by micro-hardness.

Abstract: Thermal barrier coatings (TBCs), which comprise metallic and ceramic multilayers, have been widely used in the hot section of aeroturbine engines to increase turbine efficiency and to extend the life of metallic components. An improvement in TBCs requires a better understanding of the complex changes in their structure and properties that occur under harsh operating conditions that eventually lead to their failure. In this paper, the developments of TBCs over the past 30 years are briefly reviewed. A description of materials issues involved in the state-of-art and next generation TBCs systems is presented, together with a summary of the current understanding of failure mechanisms; highlighting the challenges and prospects in TBCs research.