Interaction of Strontium Zirconate Plasma Sprayed Coating with Natural Silicate (CMAS) Dust—Origin of Luminescent Phases

Abstract

Strontium zirconate (SrZrO3) commercial powder was plasma sprayed using a high-feedrate water-stabilized plasma system (WSP) torch. Coatings with a thickness of about 1 mm were produced. Now, we are concentrating on a topic never addressed for pure SrZrO3 coatings: how the coatings interact with natural dust, known as calcium-magnesium-aluminum-silicate (CMAS). We selected various regimes of thermal treatment where SrZrO3 coatings were exposed to CMAS, and studied chemical changes, phase changes and the microstructure evolution of the influenced coatings. Microhardness of the exposed coatings was monitored as well. The results would help to understand, how the excellent refractory material SrZrO3 interacts with natural silicates. We kept in mind that pure SrZrO3 is not optimal for a thermal barrier application because of high-temperature phase transformations, but to study the CMAS-induced phenomena in more complex compositions, for example La2Zr2O7-SrZrO3, is difficult and interpretations have not been completed currently. The value of the actual research is in the separation of the phenomena typical just for SrZrO3. A potential for newly developed phases to serve as a sacrificial components of various barrier-coating systems is discussed. Several physical aspects of the newly developed components are discussed as well, namely the luminescence. Here the dust-based phases shifted down the temperature at which luminescence can occur in pure SrZrO3 ceramics. The entire thickness of influenced layers was relatively high, around 300 µm. The amorphous component, predominant after short-term CMAS exposure, was subsequently crystallized to various phases, namely SrSiO3 and monoclinic as well as tetragonal zirconia.